The geological time scale is used by geologists and other scientists to describe the timing and relationships between events that have occurred during the history of the Earth. While "period" is itself a subdivision of this scale, it is used colloquially in the name of this type to include all subdivisions of the scale.
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The Proterozoic ( /ˌproʊtərɵˈzoʊ.ɨk/) is a geological eon representing the time just before the proliferation of complex life on Earth. The name Proterozoic comes from Greek and means "earlier life". The Proterozoic Eon extended from 2,500 Ma to 542.0±1.0 Ma (million years ago), and is the most recent part of the informally named "Precambrian" time. It is subdivided into three geologic eras (from oldest to youngest): the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic.
The well-identified events of this eon were the transition to an oxygenated atmosphere during the Mesoproterozoic; several glaciations, including the hypothesized Snowball Earth during the Cryogenian period in the late Neoproterozoic; and the Ediacaran Period (635 to 542 Ma) which is characterized by the evolution of abundant soft-bodied multicellular organisms.
The geologic record of the Proterozoic is much better than that for the preceding Archean. In contrast to the deep-water deposits of the Archean, the Proterozoic features many strata that were laid down in extensive shallow epicontinental seas; furthermore, many of these rocks are less metamorphosed than Archean-age ones, and plenty are unaltered. Study
The Uintan North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 46,200,000 to 42,000,000 years BP lasting 4.2 million years. It is usually considered to fall within the Eocene epoch. The Uintan is preceded by the Bridgerian and followed by the Duchesnean NALMA stages.
The Uintan is considered to be contained within the Lutetian sharing the upper boundary and contains the following substages:
In the geologic timescale, the Homerian is the second age of the Wenlock epoch of the Silurian period of the Paleozoic era of the Phanerozoic eon that is comprehended between 426.2 ± 2.4 Ma and 422.9 ± 2.5 Ma (million years ago), approximately. The Homerian age succeeds the Sheinwoodian age and precedes the Gorstian age.
The Furongian (which represented approximately the old notions of Late Cambrian, Merioneth, Croixian, or Potsdamian) is the third and final geological epoch of the Cambrian Period. It spans the time between 501 ± 2 Ma and 488.3 ± 1.7 Ma (million years ago). It has been proposed to divided it three ICS stages, of which only the first (Paibian) is actually defined. Rocks of the Late Cambrian epoch are referred to as Upper Cambrian strata. During the Furongian, trilobites proliferated; they serve as useful index fossils. Mollusks also became more diverse and new groups such as the graptolites and the conodonts, probable early chordates, also appeared during the Furongian epoch.
The Induan is, in the geologic timescale, the first age of the Early Triassic epoch or the lowest stage of the Lower Triassic series. It spans the time between 251 ± 0.4 Ma and 249.7 ± 0.7 Ma (million years ago). It is preceded by the Changhsingian and is followed by the Olenekian.
The Induan is roughly coeval with the regional Feixianguanian stage of China.
The Induan stage was introduced into scientific literature by Russian stratigraphers in 1956, who divided the Skythian stage that was used by Western stratigraphers into the Induan and Olenekian stages. The Russian subdivision of the Lower Triassic then slowly replaced the one used in the West.
The base of the Induan stage (which is also the base of the Lower Triassic series, the base of the Triassic system and the base of the Mesozoic erathem) is defined as the place in the fossil record where the conodont species Hindeodus parvus first appears, or at the end of the negative δO anomaly after the big extinction event at the Permian-Triassic boundary. The global reference profile of the base of the Induan is situated in Changxing County, China.
The top of the Induan stage (the base of the Olenekian) is at the first appearance of
The Bridgerian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 50,300,000 to 46,200,000 years BP lasting 4.1 million years. It is usually considered to overlap the Ypresian and Lutetian within the Eocene epoch. The Bridgerian is preceded by the Wasatchian and followed by the Uintan NALMA stages.
The Bridgerian is considered to contain the following substages:
The Gzhelian is an age in the ICS geologic timescale or a stage in the stratigraphic column. It is the youngest stage of the Pennsylvanian, the youngest subsystem of the Carboniferous. The Gzhelian lasted from 303.9 ± 0.9 to 299.0 ± 0.8 Ma. It follows the Kasimovian age/stage and is followed by the Asselian age/stage, the oldest subdivision of the Permian system.
The Gzhelian is more or less coeval with the Stephanian stage of the regional stratigraphy of Europe.
The Gzhelian is named after the Russian village of Gzhel (Russian: Гжель), nearby Ramenskoye, not far from Moscow. The name and type locality were defined by Sergei Nikitin (1850–1909) in 1890.
The base of the Gzhelian is at the first appearance of the Fusulinida genera Daixina, Jigulites and Rugosofusulina, or at the first appearance of the conodont Streptognathodus zethus. The top of the stage (the base of the Permian system) is at the first appearance of the conodont Streptognathodus isolatus within the Streptognathus "wabaunsensis" chronocline. Six meters higher in the reference profile, the Fusulinida species Sphaeroschwagerina vulgaris aktjubensis appears.
At the moment (2008), a golden spike for the Gzhelian stage
The Chadronian age within the North American Land Mammal Ages chronology is the North American faunal stage typically set from 38,000,000 to 33,900,000 years BP, a period of 4.1 million years. It is usually considered to fall within the Eocene epoch. The Chadronian is preceded by the Duchesnean and followed by the Orellan NALMA stages.
The Chadronian can be further divided into the substages of:
The Chadronian maintains a period of time within the Priabonian through Rupelian of the Late Eocene through Early Oligocene in the geologic time scale.
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch (or, in chronostratigraphy: the fifth of six stages in the Upper Cretaceous series). The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma (million years ago). It is preceded by the Santonian and it is followed by the Maastrichtian.
The Campanian was introduced in scientific literature by Henri Coquand in 1857. It is named after the French village of Champagne in the département Charente-Maritime. The original type locality was an outcrop near the village of Aubeterre-sur-Dronne in the same region. Due to changes of the stratigraphic definitions, this section is now part of the Maastrichtian stage.
The base of the Campanian stage is laid at the extinction of crinoid species Marsupites testudinarius. A GSSP had not yet been ratified in 2009. One possible candidate is in a section near a dam at Waxahachie, Texas.
The top of the Campanian is defined as the place in the stratigraphic column were the ammonite Pachydiscus neubergicus first appears.
The Campanian is sometimes subdivided into Lower, Middle and Upper subages. In the Tethys domain, the Campanian encompasses six
The Oligocene (symbol OG) is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present (33.9±0.1 to 23.03±0.05 Ma). As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly uncertain. The name Oligocene comes from the Greek ὀλίγος (oligos, few) and καινός (kainos, new), and refers to the sparsity of additional modern mammalian species of fauna after a burst of evolution during the Eocene. The Oligocene follows the Eocene Epoch and is followed by the Miocene Epoch. The Oligocene is the third and final epoch of the Paleogene Period.
The Oligocene is often considered an important time of transition, a link between the archaic world of the tropical Eocene and the more modern ecosystems of the Miocene. Major changes during the Oligocene included a global expansion of grasslands, and a regression of tropical broad leaf forests to the equatorial belt.
The start of the Oligocene is marked by a notable extinction event; the replacement of European fauna with Asian fauna, except for the endemic rodent and marsupial families called
The Hettangian is the earliest age or lowest stage of the Jurassic period of the geologic timescale. It spans the time between 199.6 ± 0.6 Ma and 196.5 ± 1 Ma (million years ago). The Hettangian follows the Rhaetian (part of the Triassic period) and is followed by the Sinemurian.
In Europe stratigraphy the Hettangian is a part of the time span in which the Lias was deposited. An example is the British Blue Lias, which has an upper Rhaetian to Sinemurian age.
The Hettangian was introduced in the literature by Swiss palaeontologist, Eugène Renevier, in 1864. The stage takes its name from Hettange-Grande, a town in north-eastern France, just south of the border with Luxembourg on the main road from Luxembourg City to Metz.
The base of the Hettangian stage (which is also the base of the Lower Jurassic series and the entire Jurassic system) is defined as the place in the stratigraphic column where fossils of the ammonite genus Psiloceras first appear. A global reference profile (a GSSP) for the base had in 2009 not yet been appointed, but a section at Kuhjoch in western Austria has been proposed. The top of the Hettangian stage (the base of the Sinemurian) is at the first appearances of
The Cassinian is the latest age of the Canadian Epoch when thought of temporally and the uppermost stage of the Canadian Series when thought of stratigraphically. The Canadian, either as a series or as an Epoch is the name that has been given to the Lower, or Early, Ordovician in North America and has been applied world wide.
The Cassinian is named for the Fort Cassin Formation of Vermont. Rocks of Cassinian age are found in the Champlain Valley and among other places in North America in the Great Basin of Western Utah and Nevada, and in the uppermost El Paso Group in southern New Mexico and west Texas.
The Cassinian has been given a span of only 1.2 million years, with a range from 473 - 471.8 m.y.a. which may be short, looking at the El Paso section and Early Ordovician cephalopod evolution
In worldwide terms the Cassinian is upper, or late Arenigian which is exactly equivalent to the newly proposed Floian, both spanning the same 6.8 million years. In the four part Canadian series, the Cassinian is late upper Canadian, preceded by the Jeffersonian, and is equivalent to the upper Blackhillsian stage of the Ibexian which has been sought to replace the Canadian as the Lower
The Aalenian /ɑːˈliːniən/ is a subdivision of the Middle Jurassic epoch/series of the geologic timescale that extends from about 175.6 Ma to about 171.6 Ma (million years ago). It was preceded by the Toarcian and succeeded by the Bajocian.
The Aalenian takes its name from the town of Aalen, some 70 km east of Stuttgart in Germany. The town lies at the southwestern end of the Frankischer Jura. The name Aalenian was introduced in scientific literature by Swiss geologist Karl Mayer-Eymar in 1864.
The base of the Aalenian is defined as the place in the stratigraphic column where the ammonite genus Leioceras first appears. A global reference profile is located 500 meters north from the village of Fuentelsaz in the Spanish province of Guadalajara. The top of the Aalenian (the base of the Bajocian) is at the first appearance of ammonite genus Hyperlioceras.
In the Tethys domain, the Aalenian contains four ammonite biozones:
The Botomian age of the Early Cambrian epoch lasted from ca 524 to ca 517 Mya.
At the end of the Botomian age there was a mass extinction that wiped out a high percentage of the organisms for which fossils were found. Organisms which produced small shelly fossils were almost exterminated.
Basin Groups refers to 9 informal subdivisions of the lunar Pre-Nectarian geologic period.
The motivation for creating the Basin Groups subdivisions was to place 30 pre-Nectarian impact basins into 9 relative age groups. The relative age of the first basin in each group is based on crater densities and superposition relationships, whereas the other basins are included based on weaker grounds. Basin Group 1 has no official age for its base, and the boundary between Basin Group 9 and the Nectarian period is defined by the formation of the Nectaris impact basin.
The age of the Nectaris basin is somewhat contentious, with the most frequently cited numbers placing it at 3.92 Ga, or more infrequently at 3.85 Ga. Recently, however, it has been suggested that the Nectaris basin could be, in fact, much older and might have formed at ~4.1 Ga. Basin Groups are not used as a geologic period on any of the United States Geological Survey lunar geologic maps. Basin Groups 1-9 and the earlier (informal) Cryptic era together make up the totality of the Pre-Nectarian period.
Since little or no geological evidence on Earth exists from the time spanned by the Pre-Nectarian period of the Moon,
The Geringian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 30,800,000 to 26,300,000 years BP, a period of 4.5 million years. It is usually considered to fall within the Oligocene epoch. The Geringian is preceded by the Whitneyan and followed by the Monroecreekian NALMA stages.
The Geringian overlaps with the Rupelian and Chattian ages.
The Late Pleistocene is a geochronological age of the Pleistocene Epoch and is associated with Upper Pleistocene or Tarantian stage Pleistocence series rocks. The beginning of the stage is defined by the base of the Eemian interglacial phase before the final glacial episode of the Pleistocene 126,000 ± 5,000 years ago. The end of the age is defined as 11,700 calendar years b2k (before AD 2000). The age represents the end of the Pleistocene epoch and is followed by the Holocene epoch.
Much of the Late Pleistocene age was dominated by glaciation (the Wisconsin glaciation in North America and corresponding glacial periods in Eurasia). Many megafauna became extinct over this age, a trend that continued into the Holocene. Also, human species other than modern humans died out during the Pleistocene. Humanity spread to every continent except for Antarctica during the Late Pleistocene.
North American Land Mammal Ages within the Late Pleistocene: Rancholabrean age 0.3 Ma. Upper boundary 0.011 Ma.
In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from 245 million years ago until 237 million years ago, approximately. The Anisian age succeeds the Olenekian age (part of the Lower Triassic epoch) and precedes the Ladinian age.
The stage and its name were established by Austrian geologists Wilhelm Heinrich Waagen and Carl Diener in 1895. The name comes from Anisus, the Latin name of the river Enns. The original type locality is at Großreifling in the Austrian state of Styria.
The base of the Anisian stage (also the base of the Middel Triassic series) is sometimes laid at the first appearance of conodont species Chiosella timorensis in the stratigraphic record. Other stratigraphers prefer to use the base of magnetic chronozone MT1n. The global reference profile for the base (the GSSP or golden spike) is at a flank of the mountain Deşli Caira in the Romanian Dobruja.
The top of the Anisian (the base of the Ladinian) is at the first appearance of ammonite species Eoprotrachyceras curionii and the ammonite family Trachyceratidae. The conodont species Neogondolella praehungarica appears at the same
The Tabenbulakian age is a period of geologic time (28.4—23.03 Ma) within the Oligocene epoch of the Paleogene used more specifically with Asian Land Mammal Ages. It follows the Ulangochuian age.
The Tabenbulakian's lower boundary is the approximate base of the Chattian age and upper boundary is the approximate base of the Aquitanian age.
In the geologic timescale, the Aeronian is the age of the Llandovery epoch of the Silurian period of the Paleozoic era of the Phanerozoic eon that is comprehended between 439 ± 1.8 Ma and 436 ± 1.9 Ma (million years ago), approximately. The Aeronian age succeeds the Rhuddanian age and precedes the Telychian age, all in the same epoch.
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Ma (million years ago), to the beginning of the Permian Period, about 299.0 ± 0.8 Ma (ICS, 2004). The name Carboniferous means "coal-bearing" and derives from the Latin words carbo (coal) and ferre (to carry), and was coined by geologists William Conybeare and William Phillips in 1822. Based on a study of the British rock succession, it was the first of the modern 'system' names to be employed, and reflects the fact that many coal beds were formed globally during this time. The Carboniferous is often treated in North America as two geological periods, the earlier Mississippian and the later Pennsylvanian.
Terrestrial life was well established by the Carboniferous period. Amphibians were the dominant land vertebrates, of which one branch would eventually evolve into reptiles, the first fully terrestrial vertebrates. Arthropods were also very common, and many (such as Meganeura), were much larger than those of today. Vast swathes of forest covered the land, which would eventually be laid down and become the coal beds characteristic of the Carboniferous system. A minor
The Early Cambrian (also known as the Caerfai, Waucoban, or Georgian) is the first of three geological epochs of the Cambrian period. It spans the time between 542 ± 0.3 Ma and 513 ± 2 Ma (million years ago). The Cambrian explosion of complex organisms occurred during the Early Cambrian. The Early Cambrian is divided into two unnamed ICS stages. The rocks of the Early Cambrian are said to belong to the Lower Cambrian part of the stratigraphic succession. The Early Cambrian was a time of extreme change in both life on earth (Such as the Cambrian explosion) and in the geological land scape (such as the breakup of the Ediacaran supercontient pannotia). Abundant simple worm traces appeared to be common during during the Earliest Cambrian and in the late Ediacaran period but however they were soon followed by a set of small primitive shelled fossils known as the Small Shelly Fauna who thrived in the latest Ediacaran and the earliest Cambrian (or also known as the Manykian stage) the Small Shelly Fauna were eventually replaced by a more complex group of fossils known as the Tommotian fauna the relationship between modern fauna and the Tommotian fauna is not well known but however the
The Cambrian is the first geological period of the Paleozoic Era, lasting from 542 ± 0.3 to 488.3 ± 1.7 million years ago (mya) (ICS, 2004); it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's Cambrian rocks are best exposed. The Cambrian is unique in its unusually high proportion of lagerstätten. These are sites of exceptional preservation, where 'soft' parts of organisms are preserved as well as their more resistant shells. This means that our understanding of the Cambrian biology surpasses that of some later periods.
The Cambrian Period marked a profound change in life on Earth; prior to the Cambrian, living organisms on the whole were small, unicellular and simple. Complex, multicellular organisms gradually became more common in the millions of years immediately preceding the Cambrian, but it was not until this period that mineralised – hence readily fossilised – organisms became common. The rapid diversification of lifeforms in the Cambrian, known as the Cambrian explosion, produced the first representatives of many
The Early Pleistocene (also known as the Lower Pleistocene) is a subepoch in the international geologic timescale or a subseries in chronostratigraphy, being the earliest or lowest subdivision of the Quaternary period/system and Pleistocene epoch/series. It spans the time between 2.588 ± 0.005 Ma (million years ago) and 0.781 ± 0.005 Ma. The Early Pleistocene consists of the Gelasian and the Calabrian ages.
The Atdabanian age of the Early Cambrian epoch lasted from ca 530 to ca 524 Mya. An important Lagerstätte of the period is preserved in the Maotianshan shales. The Atdabanian Age of the Early Cambrian epoch witnessed the appearance of the first trilobites, an important class of arthropods that would flourish during the first four periods of the Paleozoic era.
The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 130.0 ± 1.5 Ma (million years ago) and 125.0 ± 1.0 Ma). It is a subdivision of the Early Cretaceous epoch (or Lower Cretaceous series). It is preceded by the Hauterivian and followed by the Aptian stage.
The Barremian falls in the Gallic epoch, a subdivision of the Cretaceous that is no longer used by the ICS. It overlaps the lower part of the Urgonian stage, which is sometimes used in western European stratigraphy. In North America, the late Coahulian and the early Comanchean correspond to the Barremian. In New Zealand, it falls within the Mokoiwian, and in Japan it corresponds to the late Aritan.
The original type locality for the Barremian stage is in the vicinity of the village of Barrême, Alpes-de-Haute-Provence, France. Henry Coquand defined the stage and named it in 1873.
The base of the Barremian is determined by the first appearance of the ammonites Spitidiscus hugii and Spitidiscus vandeckii. The end of the Barremian is determined by the geomagnetic reversal at the start of the M0r chronozone, which is biologically near the first appearance of the ammonite Paradeshayesites
The Precambrian (Pre-Cambrian) is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale. It spans from the formation of Earth about 4570 Ma (million years) ago to the beginning of the Cambrian Period, about 542 Ma, when macroscopic hard-shelled animals first appeared in abundance. The Precambrian is so named because it precedes the Cambrian, the first period of the Phanerozoic Eon, which is named after Cambria, the classical name for Wales, where rocks from this age were first studied. The Precambrian accounts for 88% of geologic time.
Not much is known about the Precambrian, despite its making up roughly seven-eighths of the Earth's history, and what little is known has largely been discovered in the past 50 years. The Precambrian fossil record is poor, and those fossils present (e.g. stromatolites) are of limited biostratigraphic use. This is because many Precambrian rocks are heavily metamorphosed, obscuring their origins, while others have either been destroyed by erosion, or remain deeply buried beneath Phanerozoic strata.
It is thought that the Earth itself
Azoic Age, Azoic Era, Azoic Period and Azoic Eon were terms used before 1950 to describe the age of rocks formed before the appearance of life in the geologic sequence. The word "Azoic" is derived from the Greek a- meaning without and zoön meaning animal (or living being), it was first used to mean without life.
Azoic was used as early as 1846 by a geologist named Adams, and gradually replaced the earlier term Primitive. Due to the controversy over evolution, "Azoic" was replaced, by 1900, in most usages by the term "Archaean" or "Archaeozic". The Archaean was later subdivided into the Archaean and the even earlier Hadean. Many of the rocks that had originally been thought to be of Azoic time were reclassified as Archaean, but the period itself is now essentially the Hadean.
Dana in 1863, said that the Azoic "stands as the first [age] in geologic history, whether science can point out unquestionably the rocks of that age or not." He went on to say that when fossils had been found in strata which had previously been classified as Azoic, the boundary was simply moved lower. "Such changes are part of the progress of the science."
The Hauterivian is, in the geologic timescale, an age in the Early Cretaceous epoch or a stage in the Lower Cretaceous series. It spans the time between 136.4 ± 2 Ma and 130 ± 1.5 Ma (million years ago). The Hauterivian is preceded by the Valanginian and succeeded by the Barremian.
The Hauterivian was introduced in scientific literature by Swiss geologist Eugène Renevier in 1873. It is named after the Swiss town of Hauterive at the shore of Lake Neuchâtel.
The base of the Hauterivian is defined as the place in the stratigraphic column where the ammonite genus Acanthodiscus first appears. A reference profile for the base (a GSSP) had in 2009 not yet been established. The top of the Hauterivian (the base of the Barremian) is at the first appearance of ammonite species Spitidiscus hugii.
In the ammonite biostratigraphy of the Tethys domain, the Hauterivian contains seven ammonite biozones:
The Middle Mississippian is the second of three subepochs of the Mississippian epoch of the Carboniferous period. It spans the time between 345.3 ± 2.1 Ma and 326.4 ± 1.6 Ma (million years ago). It has one faunal stage, the Visean.
The Pleistocene ( /ˈplaɪstəsiːn/) (symbol PS) is the geological epoch which lasted from about 2,588,000 to 11,700 years ago, spanning the world's recent period of repeated glaciations. The name Pleistocene is derived from the Greek πλεῖστος (pleistos "most") and καινός (kainos "new").
Sir Charles Lyell introduced this term in 1839 to describe strata in Sicily that had at least 70% of their molluscan fauna still living today. This distinguished it from the older Pliocene Epoch, which Lyell had originally thought to be the youngest fossil rock layer.
The Pleistocene Epoch follows the Pliocene Epoch and is followed by the Holocene epoch. The Pleistocene is the first epoch of the Quaternary Period or sixth epoch of the Cenozoic Era. The end of the Pleistocene corresponds with the end of the last glacial period. It also corresponds with the end of the Paleolithic age used in archaeology.
In the ICS timescale, the Pleistocene is divided into four stages or ages, the Gelasian, Calabrian, Ionian and Tarantian. All of these stages were defined in southern Europe. In addition to this international subdivision, various regional subdivisions are often used.
Before a change finally confirmed in
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 million years ago (mya), to the beginning of the Devonian Period, about 416.0 ± 2.8 mya (ICS, 2004). As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by several million years. The base of the Silurian is set at a major extinction event when 60% of marine species were wiped out. See Ordovician-Silurian extinction events.
A significant evolutionary milestone during the Silurian was the appearance of jawed and bony fish. Life also began to appear on land in the form of small, moss-like, vascular plants which grew beside lakes, streams, and coastlines. However, terrestrial life would not greatly diversify and affect the landscape until the Devonian.
The Silurian system was first identified by British geologist Sir Roderick Impey Murchison, who was examining fossil-bearing sedimentary rock strata in south Wales in the early 1830s. He named the sequences for a Celtic tribe of Wales, the Silures, inspired by his friend Adam Sedgwick, who had named the period of his study the Cambrian,
The Emsian is one of three faunal stages in the Early Devonian epoch. It lasted from 407 ± 2.8 million years ago to 397.5 ± 2.7 million years ago. It was preceded by the Pragian stage and followed by the Eifelian stage.
In North America the Emsian Stage is represented by Sawkill or Sawkillian time.
The Puercan North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 65,000,000 to 63,300,000 years BP lasting 1.7 million years . It is usually considered to be within the Paleocene. The Puercan is followed by the Torrejonian NALMA stage.
The Puercan is considered to contain the following substages:
The Anthropocene is an informal geologic chronological term that serves to mark the evidence and extent of human activities that have had a significant global impact on the Earth's ecosystems. The term was coined recently by ecologist Eugene F. Stoermer, but has been widely popularized by the Nobel Prize-winning atmospheric chemist, Paul Crutzen, who regards the influence of human behavior on the Earth's atmosphere in recent centuries as so significant as to constitute a new geological era for its lithosphere. To date, the term has not been adopted as part of the official nomenclature of the geological field of study.
In 2008 a proposal was presented to the Stratigraphy Commission of the Geological Society of London to make the Anthropocene a formal unit of geological epoch divisions. A large majority of that Stratigraphy Commission decided the proposal had merit and should therefore be examined further. Steps are being taken by independent working groups of scientists from various geological societies to determine whether the Anthropocene will be formally accepted into the Geological Time Scale.
Many scientists are now using the term and the Geological Society of America entitled
The Darriwilian faunal stage includes most of the Late Llanwirn.
In the geologic timescale, the Darriwilian is the age of the Middle Ordovician epoch of the Ordovician period of the Paleozoic era of the Phanerozoic eon that is comprehended between 468.1 ± 1.6 Ma and 460.9 ± 1.6 Ma (million years ago), approximately.
The Calymmian (from Greek calymma, "cover") is the first geologic period in the Mesoproterozoic Era and lasted from 1600 Mya to 1400 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.
The period is characterised by expansion of existing platform covers, or by new platforms on recently cratonized basements.
The supercontinent Columbia broke up during the Calymmian some 1500 Mya.
The Eocene (symbol EO) epoch, lasting from about 56 to 34 million years ago (55.8±0.2 to 33.9±0.1 Ma), is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the Eocene is marked by the emergence of the first modern mammals. The end is set at a major extinction event called the Grande Coupure (the "Great Break" in continuity) or the Eocene–Oligocene extinction event, which may be related to the impact of one or more large bolides in Siberia and in what is now Chesapeake Bay. As with other geologic periods, the strata that define the start and end of the epoch are well identified, though their exact dates are slightly uncertain.
The name Eocene comes from the Greek ἠώς (eos, dawn) and καινός (kainos, new) and refers to the "dawn" of modern ('new') mammalian fauna that appeared during the epoch.
The Eocene epoch is usually broken into Early and Late, or - more usually - Early, Middle, and Late subdivisions. The corresponding rocks are referred to as Lower, Middle, and Upper Eocene. The Faunal stages from youngest
The Middle Cambrian (also known as Albertan, Acadian, St. David's, or Saint David's) is the second of three geological epochs of the Cambrian period. It spans the time between 513 ± 2 Ma and 501 ± 2 Ma (million years ago). The strange organisms of the Burgess Shale fossil site lived during this epoch. The Middle Cambrian is divided into two unnamed ICS stages.
The Clarendonian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 13,600,000 to 10,300,000 years BP, a period of 3.3 million years. It is usually considered to overlap the Serravallian of the Middle Miocene epoch and Tortonian epoch of the Late Miocene. The Clarendonian is preceded by the Barstovian and followed by the Hemphillian NALMA stages.
The Clarendonian can be further divided into the substages of:
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya (million years ago), to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya (ICS, 2004). It is named after Devon, England, where rocks from this period were first studied.
The Devonian period experienced the first significant adaptive radiation of terrestrial life. Since large vertebrate terrestrial herbivores had not yet appeared, free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents. By the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods also became well-established. Fish reached substantial diversity during this time, leading the Devonian to often be dubbed the "Age of Fish". The first ray-finned and lobe-finned bony fish appeared, while the placoderms began dominating almost every known aquatic environment.
The ancestors of all tetrapods began adapting to walking on land, their strong pectoral and pelvic fins gradually evolved into legs
In the geologic record the Eoarchean erathem /ˌiːoʊ.ɑrˈkiːən/ (also spelled Eoarchaean) and the Eoarchean era in the geologic timescale correspond to one another in the dual system of classification of rock strata laid down beginning 4000 Ma to 3600 Ma (million years ago). The approximate abiotic origins of life (abiogenesis) have been dated to a time window from 3.9 to 3.5 Ga ago when atmospheric pressure values ranged from ca. 100 bar to ca. 10 bar
It was formerly officially unnamed and usually referred to as the first part of the Early Archean (now an obsolete name) together with the later Paleoarchean Era. It is the first part of the Archaean Eon, preceded by the "informal" Hadean Eon, during which the Earth was considered to be essentially molten.
The International Commission on Stratigraphy currently does not recognize the lower boundary of the era which has been provisionally placed at 4000 Ma nor that of the preceding Hadean Eon.
The Eoarchean was followed by the Paleoarchean Era.
The name comes from two Greek words: eos (dawn) and archaios (ancient). The first supercontinent Vaalbara appeared around the end of this period around 3600 ma.
A characteristic of the Eoarchean
The Cenomanian is, in the ICS' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology: it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding age. Both age and stage bear the same name.
As a unit of geologic time measure, the Cenomanian age spans the time between 99.6 ± 0.9 Ma and 93.5 ± 0.8 Ma (million years ago). In the geologic timescale it is preceded by the Albian and is followed by the Turonian.
The Cenomanian is coeval with the Woodbinian of the regional timescale of the Mexican Gulf and the Eaglefordian of the regional timescale of the US eastcoast.
At the end of the Cenomanian an anoxic event took place, called the Cenomanian-Turonian boundary event or the "Bonarelli Event", that is associated with a minor extinction event for marine species.
The Cenomanian was introduced in scientific literature by French palaeontologist Alcide d'Orbigny in 1847. Its name comes from the New Latin name of the French city of Le Mans (département Sarthe), Cenomanum.
The base of the Cenomanian stage (which is also the base of the Upper
The Early Mississippian (also known as the Lower Mississippian) is the first of three subepochs of the Mississippian epoch of the Carboniferous period. It spans the time between 359.2 ± 2.5 Ma and 345.3 ± 2.1 Ma (million years ago). It has one faunal stage, the Tournaisian.
The Eifelian is one of two faunal stages in the Middle Devonian epoch. It lasted from 397.5 ± 2.7 million years ago to 391.8 ± 2.7 million years ago. It was preceded by the Emsian stage and followed by the Givetian stage.
North American subdivisions of the Eifelian Stage include Southwood, Cazenovia (pars), and Cazenovian (pars).
Named after the Eifel Hills located in Western Germany where the GSSP is exposed in the Wetteldorf Richtschnitt.
The Famennian is one of two faunal stages in the Late Devonian epoch. It lasted from 374.5 ± 2.6 million years ago to 359.2 ± 2.5 million years ago. It was preceded by the Frasnian stage and followed by the Tournaisian stage and is named after Famenne, a natural region in southern Belgium.
It was during this age that tetrapods first appeared. In the seas, a novel major group of ammonoid cephalopods called clymeniids appeared, underwent tremendous diversification and spread worldwide, then just as suddenly went extinct.
The beginning of the Famennian is marked by a major extinction event, and the end with a smaller but still quite severe extinction event.
North American subdivisions of the Famennian include the Chautauquan, Canadaway, Conneaut, Conneautan, Conewango and Conewangan.
In the geologic timescale, the Ludfordian is the age of the Ludlow epoch of the Silurian period of the Paleozoic era of the Phanerozoic eon that is comprehended between 421.3 ± 2.6Ma and 418.7 ± 2.7 Ma (million years ago), approximately. The Ludfordian age succeeds the Gorstian age and precedes the Pridoli epoch. The Lau event is a rapid pulse of cooling during the Ludfordian, about 420 million years ago; it is identified by a pulse of extinctions and oceanic changes. It is one of the series of fast sea-level and excursions in oxygen isotope ratios that signal fast switches between warm and cold climate states, characteristic of the Silurian climatic instability. The Lau Event occurred during an extended period of elevated seawater saturation state, explained by reservoirs of the planet's fresh water being locked up in massive polar ice caps. The sudden reappearance in normally saline marine environments of stromatolites and a mass occurrence of oncoids during the event suggested that minor extinction events like the Lau Event also resulted in periods of reduced grazing pressures on surviving "disaster biota", which can be compared to the aftermath of the more catastrophic
The Muschelkalk (German: shellbearing limestone, French: calcaire coquillier) is a sequence of sedimentary rock strata (a lithostratigraphic unit) in the geology of central and western Europe. It has a Middle Triassic (240 to 230 million years) age and forms the middle part of the Germanic Trias, that further consists of the Buntsandstein (lower part) and Keuper (upper part). The Muschelkalk consists of a sequence of limestone and dolostone beds.
In the past the time span in which the Muschelkalk was deposited could also be called Muschelkalk. In modern stratigraphy however, the name only applies to the stratigraphic unit.
The name Muschelkalk was first used by German geologist Georg Christian Füchsel (1722-1773). In 1834, Friedrich August von Alberti included it into the Triassic system. The name indicates a characteristic feature of the unit, namely the frequent occurrence of lenticular banks composed of fossil shells. The Muschelkalk is restricted to the subsurface of Germany and adjacent regions as the low countries, the North Sea and parts of Silesia, Poland and Denmark. Outcrops are found in Thuringia, the Harz, Franconia, Hesse, Swabia, and the Saarland and the Alsace.
The Rancholabrean North American Land Mammal Age on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from less than 240,000 years to 11,000 years BP, a period of 0.289 million years. Named after the famed Rancho La Brea fossil site (more commonly known as the La Brea tar pits) in Los Angeles, California, the Rancholabrean is characterized by the presence of the genus Bison in a Pleistocene context, often in association with other extinct Pleistocene forms such as Mammuthus. The age is usually considered to overlap the Middle Pleistocene and Late Pleistocene epochs. The Rancholabrean is preceded by the Irvingtonian NALMA stage.
The Rancholabrean can be further divided into the substages of:
The Rancholabrean shares this time period with the Oldenburgian of European Land Mammal Ages.
The Hemingfordian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 20,600,000 to 16,300,000 years BP. It is usually considered to overlap the Early Miocene. The Hemingfordian is preceded by the Arikareean and followed by the Barstovian NALMA stages.
The Hemingfordian can be further divided into the substages of:
The Kekeamuan age is a period of geologic time (33.9—28.4 Ma) within the Early Oligocene epoch of the Paleogene used more specifically with Asian Land Mammal Ages. It follows the Houldjinian and precedes the Hsandagolian age.
The Kekeamuan's upper boundary is the approximate base of the Chattian age.
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.2 ± 4.0 to 145.5 ± 4.0 million years ago (Ma), which is preserved in Upper Jurassic strata. In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age. In the past, this name was also used to indicate the unit of geological time, but this usage is now discouraged to make a clear distinction between lithostratigraphic and geochronologic/chronostratigraphic units.
The Late Jurassic is divided into three ages, which correspond with the three (faunal) stages of Upper Jurassic rock:
During the Late Jurassic epoch, Pangaea broke up into two supercontinents, Laurasia to the north, and Gondwana to the south. The result of this break-up was the spawning of the Atlantic Ocean. However, at this time, the Atlantic Ocean was relatively narrow.
This epoch is well known for many famous types of dinosaurs, such as the sauropods, the theropods, the thyreophorans, and the ornithopods. Other animals, such as crocodiles and the first birds, appeared in the Jurassic. Listed here are only a few of the many Jurassic animals:
In geology, Neocomian was a name given to the lowest stage of the Cretaceous system. It was introduced by Jules Thurmann in 1835 on account of the development of these rocks at Neuchâtel (Neocomum), Switzerland. It has been employed in more than one sense. In the type area the rocks have been divided into two sub-stages, a lower, Valanginian (from Valengin, E. Desor, 1854) and an upper, Hauterivian (from Elauterive, E. Renevier, 1874); there is also another local sub-stage, the infra-Valanginian or Berriasian (from Berrias, H. Coquand, 1876). These three sub-stages constitute the Neocomian in its restricted sense. A. von Koenen and other German geologists extend the use of the term to include the whole of the Lower Cretaceous up to the top of the Gault or Albian. Eugène Renevier divided the Lower Cretaceous into the Neocomian division, embracing the three sub-stages mentioned above, and an Urgonian division, including the Barremian, Rhodanian and Aptian sub-stages. Sir A. Geikie (Text Book of Geology, 4th ed., 1903) regards Neocomian as synonymous with Lower Cretaceous, and he, like Renevier, closes this portion of the system at the top of the Lower Greensand (Aptian). Other
The Huronian glaciation (or Makganyene glaciation) extended from 2400 Mya to 2100 Mya, during the Siderian and Rhyacian periods of the Paleoproterozoic era, triggered by the Great Oxygenation Event (GOE), which oxidised the atmospheric methane (a greenhouse gas). It was one of the most severe and longest ice ages in geologic history, similar to the Snowball Earth ice ages that happened in the Neoproterozoic era. It was named due to evidence collected from Lake Huron region in North America where three separate horizons of glacial deposits are separated by non-glacial sediment.
The cause of the Huronian glaciation is not settled:
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series. The Cretaceous is named after the white limestone known as chalk which occurs widely in northern France and is famously seen in the white cliffs of south-eastern England, and which dates from this time.
During the Late Cretaceous, the climate was warmer than present, although throughout the period a cooling trend is evident. The tropics became restricted to equatorial regions and northern latitudes experienced markedly more seasonal climatic conditions.
Due to plate tectonics, the Americas were gradually moving westward, causing the Atlantic Ocean to expand. The Western Interior Seaway divided North America into eastern and western halves; Appalachia and Laramidia. India maintained a northward course towards Asia. In the southern hemisphere, Australia and Antarctica seem to have remained connected and began to drift away from Africa and South America. Europe was an island chain. Populating some of these islands were endemic dwarf dinosaur species.
This was a period of great success for
The Lutetian is, in the geologic timescale, a stage or age in the Eocene. It spans the time between 48.6±0.2 and 40.4±0.2 Ma. The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it is sometimes referred to as the Middle Eocene subepoch. Less often, the Middle Eocene is not used and the Lutetian is united with the Ypresian in the Early Eocene.
The Lutetian was named after Lutetia, the Latin name for the city of Paris. The Lutetian stage was introduced in scientific literature by French geologist Albert de Lapparent in 1883.
The base of the Lutetian stage is at the first appearance of the foram genus Hantkenina. An official reference profile (GSSP) for the base of the Lutetian had in 2009 not yet been established. Two candidates are located in Spain.
The top of the Lutetian (the base of the Bartonian) is at the first appearance of calcareous nannoplankton species Reticulofenestra reticulata.
The Lutetian overlaps with the Geiseltalian and lower Robiacian European Land Mammal Mega Zones (The Lutetian stage spans the Mammal Paleogene zones 11 through 15.), the upper Bridgerian and Uintan North American Land Mammal Ages, the upper
The Namurian is a stage in the regional stratigraphy of northwest Europe with an age between roughly 326 and 313 Ma (million years ago). It is a subdivision of the Carboniferous system or period and the regional Silesian series. The Namurian is named for the Belgian city and province of Namur where strata of this age occur (part of the Belgian Coal Measures). The Millstone Grit Group in the lithostratigraphy of northern England and parts of Wales is also of Namurian age.
The Namurian age lasted from 326 to 313 million years ago. It is preceded by the Visean stage/age (which corresponds to the upper Carboniferous Limestone of Great Britain) and succeeded by the Westphalian stage/age (which corresponds to the lower and middle Coal Measures of Great Britain). In the official geologic timescale of the ICS, the Namurian straddles the boundary between the Mississippian epoch (359-318 Ma) and the Pennsylvanian epoch (318-299 Ma).
The upper part of the (regionally defined) Namurian stage corresponds to the (internationally used) Bashkirian stage whilst the lower part is assigned to the preceding Serpukhovian stage. Frequent references appear in scientific literature to a Namurian epoch or
The Ochoan is a stage in the Permian stratigraphy (and an age in the geologic timescale) of North America. The Ochoan age is roughly simultaneous with the Changhsingian age in the timescale of the ICS. This post-Guadalupian stage is known for high levels of evaporite deposits.
In the geologic timescale, the Olenekian is an age in the Early Triassic epoch or a stage in the Lower Triassic series. It spans the time between 249.7 ± 0.7 Ma and 245 ± 0.7 Ma (million years ago). The Olenekian follows the Induan and is followed by the Anisian.
The Olenekian saw the deposition of a large part of the Buntsandstein in Europe. Archosaurs - a group encompassing crocodiles, pterosaurs, dinosaurs, and ultimately birds - are diapsid reptiles that first evolved from Archosauriform ancestors during the Olenekian.
The Olenekian is roughly coeval with the regional Yongningzhenian stage used in China.
The Olenekian stage was introduced into scientific literature by Russian stratigraphers in 1956. The stage is named after Olenëk in Siberia. Before the subdivision in Olenekian and Induan became commongood, both stages formed the Skythian stage, which has since disappeared from the official timescale.
The base of the Olenekian is at the lowest occurrence of the ammonites Hedenstroemia or Meekoceras gracilitatis, and of the conodont Neospathodus waageni. It is defined as ending near the lowest occurrences of genera Japonites, Paradanubites, and Paracrochordiceras; and of the
The Paleozoic Era (from the Greek palaios (παλαιός), "old" and zoe (ζωή), "life", meaning "ancient life") is the earliest of three geologic eras of the Phanerozoic Eon, spanning from roughly 542 to 251 million years ago (ICS, 2004). It is the longest of the Phanerozoic eras, and is subdivided into six geologic periods (from oldest to youngest): the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. The Paleozoic comes after the Neoproterozoic era of the Proterozoic eon, and is followed by the Mesozoic era.
The Paleozoic was a time of dramatic geological, climatic, and evolutionary change. The Cambrian Period witnessed the most rapid and widespread diversification of life in Earth's history, known as the Cambrian explosion, in which most modern phyla first appeared. Fish, arthropods, amphibians and reptiles all evolved during the Paleozoic. Life began in the ocean but eventually transitioned onto land, and by the late Paleozoic, it was dominated by various forms of organisms. Great forests of primitive plants covered the continents, many of which formed the coal beds of Europe and eastern North America. Towards the end of the era, large, sophisticated reptiles
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present. The relatively short period is characterized by a series of glaciations, the appearance and expansion of anatomically modern humans, and their continuing impact on the natural world. The Quaternary includes two geologic epochs: the Pleistocene and Holocene. A proposed but as of yet informal third epoch, the Anthropocene, has also gained credence as the time in which humans began to profoundly affect and change the global environment, although its start date is still disputed.
The term Quaternary ("fourth") was proposed by Giovanni Arduino in 1759 for alluvial deposits in the Po river valley in northern Italy. It was introduced by Jules Desnoyers in 1829 for sediments of France's Seine Basin that seemed clearly to be younger than Tertiary Period rocks. The Quaternary Period follows the Tertiary Period and extends to the present. The Quaternary covers the time span of glaciations classified as the Pleistocene, and includes the present interglacial period, the Holocene. This
Tertiary is an officially deprecated but still widely used term for a geologic period from 65 million to 2.6 million years ago, a time span that lies between the superseded Secondary period and the Quaternary. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start of the Cenozoic Era, spanning to the beginning of the most recent ice age at the end of the Pliocene Epoch. The Tertiary also included the early Pleistocene.
The Tertiary is no longer recognized as a formal unit by the International Commission on Stratigraphy, its traditional span being divided between the Paleogene and Neogene Periods of the Cenozoic Era.
The term Tertiary was first used by Giovanni Arduino during the mid-18th century. He classified geologic time into primitive (or primary), secondary, and tertiary periods based on observations of geology in northern Italy. Later a fourth period, the Quaternary, was applied. In the early development of the study of geology, the periods were thought to correspond to the Biblical narrative, the rocks of the Tertiary being thought to be associated with the Great Flood. In 1828, Charles Lyell incorporated a
The Arikareean North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 30,600,000 to 20,800,000 years BP, a period of 9.8 million years. It is usually considered to overlap the Oligocene and Miocene epochs and end by the early Pleistocene. The Arikareean is preceded by the Whitneyan and followed by the Hemingfordian NALMA stages.
The Arikareean can be further divided into the substages of:
The Rupelian is, in the geologic timescale, the older of two ages or the lower of two stages of the Oligocene epoch/series. It spans the time between 33.9±0.1 and 28.4±0.1 Ma. It is preceded by the Priabonian stage (part of the Eocene) and is followed by the Chattian stage.
The stage is named after the small river Rupel in Belgium, a tributary to the Scheldt. The Belgian Rupel Group derives its name from the same source. The name Rupelian was introduced in scientific literature by Belgian geologist André Hubert Dumont in 1850. The separation between the group and the stage was made in the second half of the 20th century, when stratigraphers saw the need to distinguish between lithostratigraphic and chronostratigraphic names.
The base of the Rupelian stage (which is also the base of the Oligocene series) is at the extinction of foram genus Hantkenina. An official GSSP had not yet been assigned to the Rupelian in 2009.
The top of the Rupelian stage (the base of the Chattian) is at the extinction of the foram genus Chiloguembelina (which is also the base of foram biozone P21b).
The Rupelian overlaps the Orellan, Whitneyan and lower Arikareean North American Land Mammal Ages, the upper
The Clarkforkian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 56,800,000 to 55,400,000 years BP lasting 1.4 million years. It is usually considered to be within the Paleocene, more specifically the Late Paleocene. The Clarkforkian is preceded by the Tiffanian and followed by the Wasatchian NALMA stages.
The Clarkforkian shares its upper boundary with the Thanetian and is considered to contain the following substages:
The Bartonian is, in the ICS's geological timescale, a stage or age in the middle Eocene epoch or series. The Bartonian age spans the time between 40.4±0.2 and 37.2±0.2 Ma. It is preceded by the Lutetian and is followed by the Priabonian age.
The Bartonian stage was introduced by Swiss stratigrapher Karl Mayer-Eymar in 1857. The name derives from the coastal village Barton-on-Sea (part of New Milton) in southern England. The Barton Group, a lithostratigraphic unit from the south English Hampshire Basin, is of Bartonian age. The distinction between group and stage was made in the second part of the 20th century, when stratigraphers saw the need to distinguish between litho- and chronostratigraphy.
The base of the Bartonian is at the first appearance of the calcareous nannoplankton species Reticulofenestra reticulata. In 2009, an official reference profile (GSSP) for the base of the Bartonian had not yet been established.
The top of the Bartonian stage (the base of the Priabonian) is at the first appearance of calcareous nannoplankton species Chiasmolithus oamaruensis (which forms the base of nannoplankton biozone NP18).
The Bartonian stage overlaps part of the upper Robiacian
In the geological timescale, the Early Devonian epoch (from 416.0 ± 2.8 million years ago to 397.5 ± 2.7 million years ago) occurred during the Devonian period, after the end of the Silurian period.
The Early Devonian epoch is subdivided into three stages: Lochkovian, Pragian and Emsian.
The Early Jurassic epoch (in chronostratigraphy corresponding to the Lower Jurassic series) is the earliest of three epochs of the Jurassic period. The Early Jurassic starts immediately after the Triassic-Jurassic extinction event, 199.6 Ma (million years ago), and ends at the start of the Middle Jurassic (175.6 Ma).
Certain rocks of marine origin of this age in Europe are called "Lias" and that name was used for the period, as well, in 19th century geology.
There are two possible origins for the name Lias: the first reason is it was taken by a geologist from an English quarryman's dialect pronunciation of the word "layers"; secondly, sloops from north Cornish ports such as Bude would sail across the Bristol Channel to the Vale of Glamorgan to load up with rock from coastal limestone quarries (lias limestone from South Wales was used throughout North Devon/North Cornwall as it contains calcium carbonate to fertilise the poor quality Devonian soils of the West Country); the Cornish would pronounce the layers of limestone as 'laiyers' or 'lias'.
There are extensive Liassic outcrops around the coast of the United Kingdom, in particular in Glamorgan, North Yorkshire and Dorset. The
The Miocene (symbol MI) is a geological epoch of the Neogene Period and extends from about 23.03 to 5.332 million years ago (Ma). The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words μείων (meiōn, “less”) and καινός (kainos, “new”) and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene Epoch and is followed by the Pliocene Epoch. The Miocene is the first epoch of the Neogene Period.
The earth went from the Oligocene Epoch through the Miocene and into the Pliocene as it cooled into a series of Ice Ages. The Miocene boundaries are not marked by a single distinct global event but consist rather of regional boundaries between the warmer Oligocene and the cooler Pliocene.
The plants and animals of the Miocene were fairly modern. Mammals and birds were well-established. Whales, seals, and kelp spread. The Miocene Epoch is of particular interest to geologists and palaeoclimatologists as major phases of Himalayan Uplift had occurred during the Miocene Epoch affecting monsoonal patterns in Asia, which were interlinked with Northern Hemisphere glaciation.
The Miocene faunal stages from youngest
The Moscovian is in the ICS geologic timescale a stage or age in the Pennsylvanian, the youngest subsystem of the Carboniferous. The Moscovian age lasted from 311.7 ± 1.1 to 306.5 ± 1.0 Ma, is preceded by the Bashkirian and is followed by the Kasimovian. The Moscovian overlaps with the European regional Westphalian stage and the North American Atokan and Desmoinesian stages.
The Moscovian saw an extinction event which occurred on the land and the sea. On the land it is referred to as the Carboniferous Rainforest Collapse.
The Moscovian stage was introduced by Sergei Nikitin (1850 - 1909) in 1890, using brachiopods in the Moscow Basin of European Russia. Nikitin named the stage after Moscow, then a major city and now the capital of Russia.
The base of the Moscovian is close to the first appearances of the conodonts Declinognathodus donetzianus and Idiognathoides postsulcatus or otherwise the fusulinid Aljutovella aljutovica. Because the fusulinid species are regionally different, they can not be used for worldwide correlation. A golden spike for the Moscovian stage has yet to be defined (2008). A proposal is to use the first appearance of the conodont Diplognathodus ellesmerensis,
The Danian is the oldest age or lowermost stage of the Paleocene epoch or series, the Paleogene period or system and the Cenozoic era or erathem. The beginning of the Danian age (and the end of the precessing Maastrichtian age) is at the Cretaceous–Paleogene extinction event 65.5±0.3 Ma. The age ended 61.7±0.2 Ma, being followed by the Selandian age.
The Danian was introduced in scientific literature by German-Swiss geologist Pierre Jean Édouard Desor in 1847. It is named after the Latin name for Denmark. The Montian stage from Belgian stratigraphy (named after the city of Mons) is now considered a junior synonym and is no longer in use.
The base of the Danian is defined at the iridium anomaly which characterized the Cretaceous–Paleogene boundary (K–T boundary) in stratigraphic sections worldwide. A section in El Kef, Tunisia was appointed as a reference profile (GSSP) for this important boundary. The Danian is the oldest age of the Paleocene, defined at its base by the K-Pg boundary. It is very important because the readily recognized iridium anomaly and primitive Danian planktonic foraminifers define the base of the Danian. Danian foraminiferans repopulated the Paleocene seas
In geology, the Arenigian (or 'Arenig') refers both to a time interval during the Lower Ordovician period and also to the suite of rocks which were deposited during this interval.
The term was first used by Adam Sedgwick in 1847 with reference to the "Arenig Ashes and Porphyries" in the neighbourhood of Arenig Fawr, in Merioneth, North Wales. The rock-succession in the Arenig district has been recognized by W. G. Fearnsides (“On the Geology of Arenig Fawr and Moel Llanfnant", Q.J.G.S. vol. lxi., 1905, pp. 608–640, with maps). The above succession is divisible into:
It was to the middle series (2) that Sedgwick first applied the term "Arenig". In the typical region and in North Wales generally the Arenig series appears to be unconformable upon the Cambrian rocks; this is not the case in South Wales.
The Arenig series is represented in North Wales by the Garth Grit and Ty Obry beds, by the Shelve series of the Corndon district, the Skiddaw Slates of the Lake District, the Ballantrae Group of Ayrshire, and by the Ribband Series of slates and shale in Wicklow and Wexford. It may be mentioned here that the "Llanvirn" Series of H. Hicks was equivalent to the bifidus shale and the Lower
The Early Ordovician, also called the Lower Ordovician by geologists, is the first subdivision of the Ordovician period, and marked a great diversification in marine life, following the extinctions at the end of the Cambrian.
Trilobites are joined by many new types of organisms, including tabulate corals, strophomenid, rhynchonellid, and many new orthid brachiopods, bryozoa, planktonic graptolites and conodonts, and many types of molluscs and echinoderms, including the ophiuroids ("brittle stars") and the first starfish. Nevertheless the trilobites remain abundant, with all the Late Cambrian orders continuing, and being joined by the new group Phacopida.
The first land plants which were probably tiny non-vascular plants resembling present day liverworts also appeared during this epoch around 474 million years ago.
Although Crinoids appeared earlier in the Cambrian period they only began to become common during the Early Ordovician epoch.
The Middle Miocene is a sub-epoch of the Miocene Epoch made up of two stages: the Langhian and Serravallian stages. The Middle Miocene is preceded by the Early Miocene.
The sub-epoch lasted from 15.97 ± 0.05 Ma to 11.608 ± 0.005 Ma (million years ago). During this period, a sharp drop in global temperatures took place. This event is known as the Middle Miocene Climate Transition.
For the purposes of establishing European Land Mammal Ages this sub-epoch is equivalent to the Astaracian age.
The Dresbachian is the lower (or earlier) stage of the Late or Upper Cambrian Period in North America, equivalent to the Chinese Guzhangian which spans about 4 million years, from 501 to 497 million years ago. The term comes from the town of Dresbach which is located in southeastern Minnesota on the Mississippi River.
The Dresbachian extinction event during the Late Cambrian was the second of two severe extinctions during the first period of the Paleozoic era; the first being the End Botomian extinction event during the Middle Cambrian. According to data on extinction intensity (see below), both extinction events slashed approximately 40 percent of marine genera. However, the two are poorly documented due to a paucity of fossil evidence so early in the evolution of life.
The Dresbachian stage overlies the Middle Cambrian Albertan series, and is the lowest stage of the Upper Cambrian Croixan series, followed by the Franconian stage. The Dresbachian event was followed by the Cambro-Ordovician extinction event about 488 million years ago.
The Hadean ( /ˈheɪdiən/) is the first geologic eon of Earth and lies before the Archean. It began with the formation of the Earth about 4.5 Ga (billion years ago) and ended roughly 3.8 Ga, though the latter date varies according to different sources. The name "Hadean" derives from Hades, the Greek name for the underworld. The name is in reference to the "hellish" conditions on Earth at the time: the planet had just formed and was still very hot due to high volcanism, a partially molten surface and frequent collisions with other Solar System bodies. The geologist Preston Cloud coined the term in 1972, originally to label the period before the earliest-known rocks on Earth. W. Brian Harland later coined an almost synonymous term: the "Priscoan period". Other, older texts simply refer to the eon as the Pre-Archean.
Since few geological traces of this period remain on Earth there is no official subdivision. However, the Lunar geologic timescale embraces several major divisions relating to the Hadean and so these are sometimes used in a somewhat informal sense to refer to the same periods of time on Earth.
The Lunar divisions are:
There is a recently proposed alternative scale published
The Holocene is a geological epoch which began at the end of the Pleistocene (around 12,000 C years ago) and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words ὅλος (holos, whole or entire) and καινός (kainos, new), meaning "entirely recent". It has been identified with the current warm period, known as MIS 1 and based on that past evidence, can be considered an interglacial in the current ice age.
The Holocene also encompasses within it the growth and impacts of the human species world-wide, including all its written history and overall significant transition toward urban living in the present. Given these, a new term Anthropocene, is specifically proposed and used informally for the latest part of this epoch since approximately synchronous lithospheric evidence, or more recently atmospheric evidence, of human impacts have been found on the Earth and its ecosystems; these impacts may be considered of global significance for future evolution of living species.
It is generally accepted that the Holocene started approximately 12,000 years BP (before present day). The period follows the last glacial period (regionally known as
The Jurassic is a geologic period and system that extends from 199.6± 0.6 Ma (million years ago) to 145.5± 4 Ma; that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic Era, also known as the Age of Reptiles. The start of the period is marked by the major Triassic–Jurassic extinction event. However, the end of the period did not witness any major extinction event. The Jurassic is named after the Jura Mountains within the European Alps, where limestone strata from the period was first identified.
By the beginning of the Jurassic, the supercontinent Pangaea had begun rifting into two landmasses, Laurasia to the north and Gondwana to the south. This created more coastlines and shifted the continental climate from dry to humid, and many of the arid deserts of the Triassic were replaced by lush rainforests. Dinosaurs dominated the land, and reached their peak in this period as they diversified into a wide variety of groups. The first birds also appeared during the Jurassic, having evolved from a branch of theropod dinosaurs. The oceans were inhabited by marine reptiles such as ichthyosaurs and plesiosaurs,
The Late Hemingfordian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 20,430,000 to 16,300,000 years BP, a period of 4.1 million years. It is usually considered to overlap the Early Miocene. The Hemingfordian is preceded by the Early Barstovian and followed by the Early Hemingfordian NALMA stages.
The Neoarchean ( /ˌniː.oʊ.ɑrˈkiː.ən/; also spelled Neoarchaean) is a geologic era within the Archaean. It spans the period of time from 2,800 to 2,500 million years ago—the period being defined chronometrically and not referenced to a specific level in a rock section on Earth. Oxygenic photosynthesis first evolved in this era and was accountable for the oxygen catastrophe which was to happen later in the Paleoproterozoic from a poisonous buildup of oxygen in the atmosphere, produced by these oxygen producing photoautotrophs, which evolved earlier in the Neoarchean. The supercontinent Kenorland formed during this period, about 2.7 billion years ago.
In the geological timescale, the Berriasian is an age or stage of the Early or Lower Creteceous. It is the oldest or lowest subdivision in the entire Cretaceous. It spanned between 145.5 ± 4.0 Ma and 140.2 ± 3.0 Ma (million years ago). The Berriasian succeeds the Tithonian (part of the Jurassic) and precedes the Valanginian.
The Berriasian stage was introduced in scientific literature by Henri Coquand in 1869. It is named after the village of Berrias in the Ardèche region of France. The largely non-marine English Purbeck Formation is of Berriasian age and in the past the names Purbeck and Wealden were also used to address rocks of the lowest Cretaceous.
The base of the Berriasian (also the base of the Cretaceous system) has traditionally been placed at the first appearance of fossils of the ammonite species Berriasella jacobi. A global reference profile (a GSSP) for the Berriasian is under active consideration by the Cretaceous International Subcommission (ISCS) of IUGS. A range of contender GSSP localities are currently being studied by the ISCS's Berriasian Working Group. Several markers are being employed to refine correlations and to work towards definition of a stage base.
The Neoproterozoic Era is the unit of geologic time from 1,000 to 542.0 ± 1.0 million years ago. The terminal Era of the formal Proterozoic Eon (or the informal "Precambrian"), it is further subdivided into the Tonian, Cryogenian, and Ediacaran Periods. The most severe glaciation known in the geologic record occurred during the Cryogenian, when ice sheets reached the equator and formed a possible "Snowball Earth". The earliest fossils of multicellular life are found in the Ediacaran, including the earliest animals.
At the onset of the Neoproterozoic the supercontinent Rodinia, which had assembled during the late Mesoproterozoic, straddled the equator. During the Tonian, rifting commenced which broke Rodinia into a number of individual land masses.
Possibly as a consequence of the low-latitude position of most continents, several large-scale glacial events occurred during the Neoproterozoic Era including the Sturtian and Marinoan glaciations of the Cryogenian.
These glaciations are believed to have been so severe that there were ice sheets at the equator—a state known as the "Snowball Earth".
The Russians divide the Siberian Neoproterozoic into the Baikalian from 850 to 650Ma
The Paleogene (alternatively British English Palaeogene or Palæogene, informally Lower Tertiary) is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic Era. Lasting 42 million years, the Paleogene is most notable as being the time in which mammals evolved from relatively small, simple forms into a large group of diverse animals in the wake of the Cretaceous–Paleogene extinction event that ended the preceding Cretaceous Period. Birds also evolved considerably during this period, changing into roughly modern forms.
This period consists of the Paleocene, Eocene, and Oligocene Epochs. The end of the Paleocene (55.5/54.8 Mya) was marked by one of the most significant periods of global change during the Cenozoic, the Paleocene-Eocene Thermal Maximum, which upset oceanic and atmospheric circulation and led to the extinction of numerous deep-sea benthic foraminifera and on land, a major turnover in mammals. The Paleogene follows the Cretaceous Period and is followed by the Miocene Epoch of the Neogene Period. The terms 'Paleogene System' (formal) and 'lower Tertiary System' (informal) are applied to the
The Ectasian (from Greek ectasis, "extension") is the second geologic period in the Mesoproterozoic Era and lasted from 1400 Mya ago to 1200 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.
Name derives from continued expansion of platform covers during this period.
This period is interesting for the first evidence of sexual reproduction. The 1.2 billion year old Hunting Formation on Somerset Island, Canada, dates from the end of the Ectasian. It contains the microfossils of the multicellular filaments of Bangiomorpha pubescens (type of red algae), the first taxonomically resolved eukaryote. This was the first organism that exhibited sexual reproduction, which is an essential feature for complex multicellularity. Complex multicellularity is different from "simple" multicellularity, such as colonies of organisms living together. True multicellular organisms contain cells that are specialized for different functions. This is, in fact, an essential feature of sexual reproduction as well, since the male and female gametes are specialized cells. Organisms that reproduce sexually must solve the problem of generating an entire
The Gelasian is an age in the international geologic timescale or a stage in chronostratigraphy, being the earliest or lowest subdivision of the Quaternary period/system and Pleistocene epoch/series. It spans the time between 2.588 ± 0.005 Ma (million years ago) and 1.806 ± 0.005 Ma. It follows the Piacenzian stage (part of the Pliocene) and is followed by the Calabrian stage.
During the Gelasian the Red Crag of Butley and Newbourn and the Norwich and Weybourn Crags, all from East Anglia (England) were deposited. The Gelasian is an equivalent of the Praetiglian and Tiglian stages as defined in the Netherlands, which are commonly used in northwestern Europe.
The Gelasian was introduced in the geologic timescale in 1998. It is named after the Sicilian city of Gela in the south of the island. In 2009 it was moved from the Pliocene to the Pleistocene in order that the geologic time scale be more consistent with the key changes in Earth's climate, oceans, and biota that occurred 2.588 million years ago.
The base of the Gelasian is defined magnetostratigraphically as the base of the Matuyama (C2r) chronozone (at the Gauss-Matuyama magnetostratigraphic boundary), isotopic stage 103. Above
The Cryogenian (from Greek cryos "cold" and genesis "birth") is a geologic period that lasted from 850 to 635 million years ago. It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran. The Sturtian and Marinoan glaciations, which are the greatest ice ages known to have occurred on Earth and may have covered the entire planet, occurred during this period. These so-called 'snowball earth' events are the subject of much scientific controversy. The main debate involves whether these glaciations were truly global or merely localised events.
The period has not received the international ratification that most geological time periods undergo (the most recent being the Ediacaran Period, which was ratified in 2004). The start of the period is defined only on the ages of the rocks and not on any observable and documented global event. This is problematic as estimates of rock ages are variable and are subject to laboratory error. For instance, the Cambrian Period is marked not by rock younger than a given age (542 million years), but by the appearance of the worldwide Treptichnus pedum diagnostic trace fossil assemblage. This
The Franconian is the middle stage of the Upper or Late Cambrian in North America, equivalent to the Chinese Changshanian with a span of nearly 4.5 million years, from about 497 to 492.5 Ma. The name comes from the Franconia Formation, about 100 feet (30 m) of sandstone and green shale exposed near the town of Franconia in eastern Minnesota, north of St Paul.
The Franconian is preceded by the Dresbachian and followed by the Trempealeauan, respectively the lower and upper stages of the North American Upper Cambrain or Croixan Series.
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma (million years ago). The Maastrichtian was preceded by the Campanian and succeeded by the Danian (part of the Paleogene and Paleocene).
At the end of this period, there was a mass extinction commonly referred to as the Cretaceous–Paleogene extinction event, as well the Cretaceous–Tertiary extinction event. At this extinction event, many commonly recognized groups such as non-avian dinosaurs, plesiosaurs and mosasaurs, as well as many other lesser known groups, died out.
The Maastrichtian was introduced into scientific literature by Belgian geologist André Hubert Dumont in 1849, after studying rock strata of the Chalk Group close to the Dutch city of Maastricht. These strata are now classified as the Maastricht Formation - both formation and stage derive their names from the city. The Maastricht Formation is known for its fossils from this age, most notably those of the giant sea reptile Mosasaurus.
The base of the Maastrichtian
The Neogene is a geologic period and system in the International Commission on Stratigraphy (ICS) Geologic Timescale starting 23.03 ± 0.05 million years ago and ending 2.588 million years ago. The second period in the Cenozoic Era, it follows the Paleogene Period and is succeeded by the Quaternary Period. The Neogene is subdivided into two epochs, the earlier Miocene and the later Pliocene.
The Neogene covers about 23 million years. During this period, mammals and birds continued to evolve into roughly modern forms, while other groups of life remained relatively unchanged. Early hominids, the ancestors of humans, appeared in Africa. Some continental movement took place, the most significant event being the connection of North and South America at the Isthmus of Panama, late in the Pliocene. This cut off ocean currents between the Atlantic and Pacific oceans, causing climate changes and creating the Gulf Stream. The global climate cooled considerably over the course of the Neogene, culminating in a series of continental glaciations in the Quaternary Period that follows.
In ICS terminology, from upper (later, more recent) to lower (earlier):
The Pliocene Epoch is subdivided into 2
The Permian is a geologic period and system which extends from 299.0 ± 0.8 to 251.0 ± 0.4 Ma (Million years ago). It is the last period of the Paleozoic Era, following the Carboniferous Period and preceding the Triassic Period of the Mesozoic Era. It was first introduced in 1841 by geologist Sir Roderick Murchison, and is named after the Perm Krai in Russia, where strata from the period were originally found.
The Permian witnessed the diversification of the early amniotes into the ancestral groups of the mammals, turtles, lepidosaurs and archosaurs. The world at the time was dominated by a single supercontinent known as Pangaea, surrounded by a global ocean called Panthalassa. The extensive rainforests of the Carboniferous had disappeared, leaving behind vast regions of arid desert within the continental interior. Reptiles, who could better cope with these dryer conditions, rose to dominance in lieu of their amphibian ancestors. The Permian Period (along with the Paleozoic Era) ended with the largest mass extinction in Earth's history, in which nearly 90% of marine species and 70% of terrestrial species died out. It would take well into the Triassic for life to recover from this
The Torrejonian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 63,300,000 to 60,200,000 years BP lasting 3.1 million years. It is usually considered to overlap the Selandian and Thanetian within the Paleocene. The Torrejonian is preceded by the Puercan and followed by the Tiffanian NALMA stages.
The Torrejonian is considered to be contained within the Danian and contains the following substages:
The Wasatchian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 55,400,000 to 50,300,000 years BP lasting 5.1 million years. It is usually considered to be within the Eocene, more specifically the Early Eocene. The Wasatchian is preceded by the Clarkforkian and followed by the Bridgerian NALMA stages.
The Wasatchian is considered to contain the following substages:
Dewey Lake, located near Prestonsburg, Kentucky in Floyd County, is part of the integrated flood reduction system operated by the United States Army Corps of Engineers for the entire Ohio River Basin.
The 1,100-acre (4 km) lake was formed by impounding John's Creek in 1949, and was named for either Admiral George Dewey or local resident Dewey Wells. Dewey Dam (National ID # KY03029) is an earthen dam, 188 feet high.
Jenny Wiley State Resort Park is located on Dewey Lake.
The largest tiger muskie ever taken in the state of Kentucky (13 lb., 12 oz.) was caught in Dewey Lake.
The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene Epoch made up of two stages: the Aquitanian and Burdigalian stages.
The sub-epoch lasted from 23.03 ± 0.05 Ma to 15.97 ± 0.05 Ma (million years ago). It was preceded by the Oligocene epoch. As the climate started to get cooler, the landscape started to change. New mammals evolved to replace the extinct animals of the Oligocene epoch.The first members of the hyena and weasel family started to evolve to replace the extinct Hyaenodon, entelodonts and bear-dogs. The chalicotheres survived the Oligocene epoch. A new genus of entelodont called Daeodon evolved in order to adapt to the new habitats and hunt the new prey animals of the Early Miocene epoch; it quickly became the top predator of North America. But it became extinct due to competition from Amphicyon, a newcomer from Eurasia. Amphicyon bested Daeodon because the bear-dog's larger brain, sharper teeth and longer legs built for longer chases helped it to overcome its prey.
The Mesoproterozoic Era is a geologic era that occurred between 1600 Ma and 1000 Ma (million years ago). The Mesoproterozoic was the first period of Earth's history with a respectable geological record. Continents existed in the Paleoproterozoic, but we know little about them. The continental masses of the Mesoproterozoic are more or less the same ones that are with us today.
The major events of this era are the formation of the Rodinia supercontinent, the breakup of the Columbia supercontinent, and the evolution of sexual reproduction.
This era is marked by the further development of continental plates and plate tectonics. At the end of this era, the continental plates that had developed were more or less the same we have today. This is the first era of which a good geological record still exists today.
The first large-scale mountain building episode, the Grenville Orogeny, for which extensive evidence still survives happened in this period.
This era was the high point of the Stromatolites before they declined in the Neoproterozoic.
The era saw the development of sexual reproduction, which greatly increased the complexity of life to come. It was the start of development of
The Ayusokkanian is a Russian and Kazakhian faunal stage that occurred during the Early Cambrian period. It spans from 501 to 494.5 million years ago. The beginning of the Ayusokkanian stage is marked by the appearance of the agnostid trilobite Glyptagnostus reticulatus. It is preceded by the Mayan stage and is followed by the Sakian stage, it significantly overlaps with the Australian Idamean stage.
In the geologic timescale the Bathonian is an age or stage of the Middle Jurassic. It lasted from approximately 167.7 Ma to around 164.7 Ma (million years ago). The Bathonian age succeeds the Bajocian age and precedes the Callovian age.
The Bathonian stage takes its name from Bath, a spa town in England built on Jurassic limestone (the Latinized form of the town name is Bathonium). The name was introduced in scientific literature by Belgian geologist d'Omalius d'Halloy in 1843. The original type locality was located near Bath. The French palaeontologist Alcide d'Orbigny was in 1852 the first to define the exact length of the stage.
The base of the Bathonian is at the first appearance of ammonite species Parkinsonia (Gonolkites) convergens in the stratigraphic column. A global reference profile for the base of the Bathonian (a GSSP) had in 2009 not yet been assigned. The top of the Bathonian (the base of the Callovian stage) is at the first appearance of ammonite genus Kepplerites.
In the Tethys domain, the Bathonian contains eight ammonite biozones:
Members of the order ammonitida are known as Ammonitic ammonites. They are distinguished primarily by their suture lines. In ammonitic
The Early Cretaceous (geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 146 Ma to 100 Ma.
During this time many new types of dinosaurs appeared or came into prominence, including Psittacosaurus, spinosaurids and coelurosaurs, while other survivors from the Late Jurassic continued.
In the seas, the ichthyosaurs declined and eventually died out at the start of the Late Cretaceous. Angiosperms appear for the first time.
In the lunar geologic timescale, the Early Imbrian epoch occurred between 3850 million years ago to about 3800 million years ago. It overlaps the end of the Late Heavy Bombardment of the inner solar system. The impact which created the huge Mare Imbrium basin occurred at the start of the epoch. The other large basins that dominate the lunar nearside (such as Crisium, Tranquilitatis, Serenitatis, Fecunditatis, and Procellarum) were also formed in this period. These basins filled with basalt mostly during the subsequent Late Imbrian epoch. The Early Imbrian was preceded by the Nectarian.
Since little or no geological evidence on Earth exists from the time spanned by the Early Imbrian epoch of the Moon, the Early Imbrian has been used by at least one notable scientific work as an unofficial subdivision of the terrestrial Hadean eon.
The Guadalupian is the second of the three epoches of the Permian, it lasted from about 270 to 260 million years ago. This epoch saw coral reefs flourishing in shallow seas, and on land the replacement of the Pelycosaurs by early Therapsids.
The Messinian is in the geologic timescale the last age or uppermost stage of the Miocene. It spans the time between 7.246 ± 0.005 Ma and 5.332 ± 0.005 Ma (million years ago). It follows the Tortonian and is followed by the Zanclean, the first age of the Pliocene.
The Messinian overlaps the Turolian European Land Mammal Mega Zone (more precise MN 12 and 13) and the Pontian Central European Paratethys stage. It also overlaps the late Huayquerian and early Montehermosan South American Land Mammal Ages, and falls inside the more extensive Hemphillian North American Land Mammal Age.
During the Messinian, around 6 million years ago, the Messinian salinity crisis took place, which brought about repeated desiccations of the Mediterranean Sea.
The Messinian was introduced by Swiss stratigrapher Karl Mayer-Eymar in 1867. Its name comes from the Italian city of Messina on Sicily, where the Messinian evaporite deposit is of the same age.
The base of the Messinian is at the first appearance of the planktonic foram species Globorotalia conomiozea and is stratigraphically in the middle of magnetic chronozone C3Br.1r. The GSSP for the Messinian is located in a section at Oued Akrech, near the
The Middle Pennsylvanian is the second of three subepochs of the Pennsylvanian epoch of the Carboniferous period. It spans the time between 311.7 ± 1.1 Ma and 306.5 ± 1 Ma (million years ago). It has one faunal stage, the Moscovian.
The Selandian is in the geologic timescale an age or stage in the Paleocene. It spans the time between 61.7±0.2 and 58.7±0.2 Ma. It is preceded by the Danian and followed by the Thanetian. Sometimes the Paleocene is subdivided in subepochs, in which the Selandian forms the "Middle Paleocene".
The Selandian was introduced in scientific literature by Alfred Rosenkrantz in 1924. It is named after the Danish island of Zealand (Danish: Sjælland).
The base of the Selandian is close to the boundary between biozones NP4 and NP5. It is slightly after the first appearances of many new species of the calcareous nannoplankton genus Fasciculithus (F. ulii, F. billii, F. janii, F. involutus, F. tympaniformis and F. pileatus) and close to the first appearance of calcareous nannoplankton species Neochiastozygus perfectus. At the original type location in Denmark the base of the Selandian is an unconformity. The official GSSP was established in the Zumaia section (43° 18'N, 2° 16'W) at the beach of Itzurun, Pais Vasco, northern Spain.
The top of the Selandian (the base of the Thanetian) is laid at the base of magnetic chronozone C26n.
The Selandian stage overlaps with the lower part of the
The Blancan North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 4,750,000 to 1,808,000 years BP, a period of 2.942 million years. It is usually considered to start in the early-mid Pliocene Epoch and end by the early Pleistocene. The Blancan is preceded by the Hemphillian and followed by the Irvingtonian NALMA stages.
As usually defined, it corresponds to the mid-Zanclean through Piacenzian and Gelasian stages in Europe and Asia. In California, the Blancan roughly corresponds to the mid-Delmontian through Repettian and Venturian to the very early Wheelerian. The Australian contemporary stages are the mid-Cheltenhamian through Kalimnan and Yatalan. In New Zealand, the Opoitian starts at roughly the same time and the Blancan is further coeval with the Waipipian and Mangapanian stages to the early Nukumaruan. Finally, in Japan the Blancan starts coeval with the late Yuian, runs alongside the Totomian and Suchian and ends soon after the start of the Kechienjian.
The start date of the Blancan has not been fully established. There is general agreement that it is between
The Cenozoic Era ( /ˌsɛnəˈzoʊ.ɨk/ or /ˌsiːnəˈzoʊ.ɨk/; also Cænozoic or Cainozoic; meaning "new life", from Greek καινός kainos "new", and ζωή zoe "life") is the current and most recent of the three Phanerozoic geological eras, following the Mesozoic Era and covering the period from 65.5 Ma to the present.
The era began in the wake of the Cretaceous–Paleogene extinction event (K-Pg event) at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs (as well as other terrestrial and marine flora and fauna) at the end of the Mesozoic. The Cenozoic is also known as the Age of Mammals, because the extinction of many groups allowed mammals to greatly diversify.
Early in the Cenozoic, following the K-Pg event, the planet was dominated by relatively small fauna, including small mammals, birds, reptiles, and amphibians. From a geological perspective, it did not take long for mammals and birds to greatly diversify in the absence of the large reptiles that had dominated during the Mesozoic. Some birds grew larger than the average human. This group became known as the "terror birds," and were formidable predators. Mammals came to occupy almost every available niche (both
The Lochkovian is one of three faunal stages in the Early Devonian epoch. It lasted from 416 ± 2.8 million years ago to 411.2 ± 2.8 million years ago. It marked the beginning of the Devonian Period, and was followed by the Pragian stage.
In North America the Lochkovian Stage is represented by Gedinnian or Helderbergian time.
The Ibexian is recognized as the youngest Cambrian and oldest Ordovician series in North America.
The Ibexian Series is named for Ibex Well in Tule Valley, near the Jack Watson ranch site of Ibex, on the east side of the Barn Hills in west-central Utah. The uppermost Cambrian in the type area includes the upper Lava Dam Member of the Notch Peak Formation and the lower part of the Barn Hills Member of the House Limestone. Lowermost Ordovician strata of Ibexian age include most of the remainder of the House Limestone. The base of the Ibexian is recognized as the first occurrence of the conodont, Cordylodus andresi, and the top is recognized as the base of the Stairsian Series.
The Barstovian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 16,300,000 to 13,600,000 years BP, a period of 2.7 million years. It is usually considered to overlap the Langhian and Serravallian epochs of the Middle Miocene. The Barstovian is preceded by the Hemingfordian and followed by the Clarendonian NALMA stages.
The Barstovian can be further divided into the substages of:
The Mesoarchean ( /ˌmiːzoʊ.ɑrˈkiː.ən/, also spelled Mesoarchaean) is a geologic era within the Archean, spanning 3200 Ma to 2800 Ma (million years ago). The period is defined chronometrically and is not referenced to a specific level in a rock section on Earth. Fossils from Australia show that stromatolites have lived on Earth since the Mesoarchean. The Pongola glaciation occcured at 2.9 Ga. The first supercontinent Vaalbara broke up during this time around 2.8 Ga.
The Mississippian is a subperiod in the geologic timescale or a subsystem of the geologic record. It is the earliest/lowermost of two subperiods of the Carboniferous period lasting from roughly 359 to 318 Ma (million years ago). As with most other geochronologic units, the rock beds that define the Mississippian are well identified, but the exact start and end dates are uncertain by a few million years. The Mississippian is so named because rocks with this age are exposed in the Mississippi River valley.
In North America, where the interval consists primarily of marine limestones, it was in the past treated as a full-fledged geologic period between the Devonian and the Pennsylvanian. In Europe, the Mississippian and Pennsylvanian are one more-or-less continuous sequence of lowland continental deposits and are grouped together as the Carboniferous system, and sometimes called the Upper Carboniferous and Lower Carboniferous instead. During the Mississippian subperiod an important phase of orogeny occurred in the Appalachian Mountains.
The Mississipian was a period of marine ingression in the Northern Hemisphere: the ocean stood so high only the Fennoscandian Shield and the Laurentian
The Priabonian is, in the ICS's geologic timescale, the latest age or the upper stage of the Eocene epoch or series. It spans the time between 37.2±0.1 and 33.9±0.1 Ma. The Priabonian is preceded by the Bartonian and is followed by the Rupelian, the lowest stage of the Oligocene.
The Priabonian stage was introduced in scientific literature by Ernest Munier-Chalmas and Albert de Lapparent in 1893. The stage is named afted the small hamlet of Priabona in the community of Monte di Malo, in the Veneto region of northern Italy.
The base of the Priabonian stage is at the first appearance of calcareous nannoplankton species Chiasmolithus oamaruensis (which forms the base of nannoplankton biozone NP18). An official GSSP had in 2009 not yet been assigned.
The top of the Priabonian stage (the base of the Rupelian stage and Oligocene series) is at the extinction of foram genus Hantkenina.
Sometimes local rock strata cannot be correlated in sufficient detail with the ICS timescale, and stratigraphers often use regional timescales as alternatives to the ICS timescale. The Priabonian overlaps for example the upper Johannian and lower Aldingan stages of the Australian timescale or the upper
The Orellan North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 33,900,000 to 33,300,000 years BP, a period of 0.6 million years. It is usually considered to fall within the Early Oligocene. The Orellan precedes by the Whitneyan and follows the Chadronian NALMA stages.
The Orellan is contained within: Rupelian and shares the lower boundary.
The Aquitanian is, in the ICS' geologic timescale, the oldest age or lowest stage in the Miocene. It spans the time between 23.03 ± 0.05 Ma and 20.43 ± 0.05 Ma (million years ago) and is a dry, cooling period. The Aquitanian succeeds the Chattian (the youngest age of the Oligocene) and precedes the Burdigalian.
The Aquitanian age overlaps with the Harrisonian, Agenian, Pareora, Landon, Otaian, and Waitakian ages from various regional timescales.
The Aquitanian stage was named after the region Aquitaine in France and was introduced in scientific literature by Swiss stratigrapher Karl Mayer-Eymar in 1858.
The base of the Aquitanian (also the base of the Miocene series and the Neogene system) is defined as the place in the stratigraphic column at the first appearance of foram species Paragloborotalia kugleri, the extinction of calcareous nannoplankton species Reticulofenestra bisecta (which forms the base of nannoplankton biozone NN1), and the base of magnetic chronozone C6Cn.2n. The official GSSP for the Aquitanian stage lies in the Lemme-Carrioso section near the small village of Carrioso (north of Genoa) in northern Italy.
The top of the Aquitanian stage (the base of the
The Archean ( /ɑrˈkiːən/, also spelled Archaean; formerly Archaeozoic /ɑrkiəˈzoʊɨk/), also spelled Archeozoic or Archæozoic) is a geologic eon before the Proterozoic Eon, before 2.5 Ga (billion years, or 2,500 Ma) ago. The Archean era is generally agreed to have started at 3.8 billion years ago, but this boundary is informal.
Instead of being based on stratigraphy as all other geological ages are, the beginning of the Archean eon is defined chronometrically. The lower boundary (starting point) of 3.8 thousand million years has not been officially recognized by the International Commission on Stratigraphy.
The Archean customarily starts at 3.8 Ga—at the end of the Hadean Eon. In older literature, the Hadean is included as part of the Archean. The name comes from the ancient Greek Αρχή (Arkhē), meaning "beginning, origin".
The Archean is one of the four principal eons of Earth history. When the Archean began, the Earth's heat flow was nearly three times higher than it is today, and it was still twice the current level at the transition from the Archean to the Proterozoic (2,500 Ma). The extra heat was the result of a mix of remnant heat from planetary accretion, heat from the
The Middle Ordovician (from 472 to 461 million years ago) is the second subdivision of the Ordovician period. During this time warm shallow sea covered much of the land, and was home to a rich diversity of marine life. Traditionally the Middle Ordovician has been divided into the Llanvirn and Llandielo stages but however this division has been replaced by two newer stages known as Ordovivian III and the Darriwilian.
North America straddled the equator, while the south-polar supercontinent of Gondwana included not only South America, Africa, India, Antarctica and Australia, but Southern Europe as well.
The trilobite-dominated Early Ordovician communities are replaced by generally more mixed ecosystems, in which brachiopods, bryozoa, molluscs and echinoderms all flourish, tabulate corals diversify and the first rugose corals appear; trilobites are no longer typically predominant. The planktonic graptolites remain diverse, with the Diplograptina making their appearance. Bioerosion becomes an important process, particularly in the thick calcitic shells of corals, bryozoans and brachiopods, and on the extensive carbonate hardgrounds which appear at this time.
The earliest known armoured
In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided. It spans the time between 245 ± 1.5 Ma and 228 ± 2 Ma (million years ago). The Middle Triassic is divided into the Anisian and Ladinian ages or stages.
Formerly the middle series in the Triassic was also known as Muschelkalk. This name is now only used for a specific unit of rock strata with approximately Middle Triassic age, found in western Europe.
The Nectarian Period of the lunar geologic timescale runs from 3920 million years ago to 3850 million years ago. It is the period during which the Nectaris Basin and other major basins were formed by large impact events. Ejecta from Nectaris forms the upper part of the densely cratered terrain found in lunar highlands.
Since little or no geological evidence on Earth exists from the time spanned by the Nectarian period of the Moon, the Nectarian has been used by at least one notable scientific work as an unofficial subdivision of the terrestrial Hadean eon.
'The Nectarians' is also the name of a secret organisation, dedicated to preserving balance in the world, in the story 'The Rise of Raikasen'.
The Norian is a division of the Triassic geological period. It has the rank of an age (geochronology) or stage (chronostratigraphy). The Norian lasted from 216.5 ± 2.0 to 203.6 ± 1.5 million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.
The Norian was named after the Noric Alps in Austria. The stage was introduced into scientific literature by Austrian geologist Edmund Mojsisovics von Mojsvar in 1869.
The Norian stage begins at the base of the ammonite biozones of Klamathites macrolobatus and Stikinoceras kerri, and at the base of the conodont biozones of Metapolygnathus communisti and Metapolygnathus primitius. A global reference profile for the base (a GSSP) had in 2009 not yet been appointed.
The top of the Norian (the base of the Rhaetian) is at the first appearance of ammonite species Cochloceras amoenum. The base of the Rheatian is also close to the first appearance of conodont species Misikella spp. and Epigondolella mosheri and the radiolarid species Proparvicingula moniliformis.
In the Tethys domain, the Norian stage contains six ammonite biozones:
The Whitneyan North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 33,300,000 to 30,800,000 years BP, a period of 2.5 million years. It is usually considered to fall within the Early Oligocene. The Whitneyan is preceded by the Orellan and followed by the Arikareean NALMA stages.
The Whitneyan is interchangeable with the Rupelian age.
In the geologic timescale, the Callovian is an age or stage in the Middle Jurassic, lasting between 164.7 ± 4.0 Ma (million years ago) and 161.2 ± 4.0 Ma. It is the last stage of the Middle Jurassic, following the Bathonian and preceding the Oxfordian.
The Callovian stage was first described by French palaeontologist Alcide d'Orbigny in 1852. Its name derives from the latinized name for Kellaways Bridge, a small hamlet 3 km north-east of Chippenham, Wiltshire, England.
The base of the Callovian is defined as the place in the stratigraphic column where the ammonite genus Kepplerites first appears, which is the base of the biozone of Macrocephalites herveyi. A global reference profile (a GSSP) for the base had in 2009 not yet been assigned.
The top of the Callovian (the base of the Oxfordian) is at the first appearance of ammonite species Brightia thuouxensis.
The Callovian is often subdivided into three substages (or subages): Lower/Early, Middle and Upper/Late Callovian. In the Tethys domain, the Callovian encompasses six ammonite biozones:
During the Callovian, Europe was an Archipelago of a dozen or so large islands. Between them were extensive areas of continental shelf.
In the geologic timescale, the Changhsingian or Changxingian (from Chinese: 长兴县, Pinyin: Chángxìng Xiàn, "Changxing County") is the latest age or uppermost stage of the Permian. It is also the upper or latest of two subdivisions of the Lopingian epoch or series. The Changhsingian lasted from 253.8 ± 0.7 to 251.0 ± 0.7 million years ago (Ma). It was preceded by the Wuchiapingian and followed by the Induan.
The greatest mass extinction event in the Phanerozoic eon occurred during this age. The extinction rate peaked about a million years before the end of this stage.
The Changhsingian is named after Changxing County in China (Wades-Giles transcription: Ch’ang-hsing). The stage was named for the Changhsing Limestone. The name was first used for a stage in 1970 and was anchored in the international timescale in 1981.
The base of the Changhsingian stage is at the first appearance of conodont species Clarkina wangi. The global reference profile is profile D at Meishan, in the type area in Changxing. The top of the Changhsingian (the base of the Induan stage and the Triassic system is at the first appearance of conodont species Hindeodus parvus.
The Changhsingian stage contains only one
In the geologic timescale, the Gorstian is the age of the Ludlow epoch of the Silurian period of the Paleozoic era of the Phanerozoic eon that is comprehended between 422.9 ± 2.5 Ma and 421.3 ± 2.6 Ma (million years ago), approximately. The Gorstian age succeeds the Homerian age and precedes the Ludfordian age.
The Hemphillian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 10,300,000 to 4,900,000 years BP, a period of 5.4 million years. It is usually considered to overlap the Tortonian epoch of the Late Miocene and Zanclean epoch of the Early Pliocene. The Hemphillian is preceded by the Clarendonian and followed by the Blancan NALMA stages.
The Hemphillian can be further divided into the substages of:
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 112.0 ± 1.0 Ma (million years ago), approximately. The Aptian succeeds the Barremian and precedes the Albian, all part of the Lower/Early Cretaceous.
The Aptian partly overlaps the upper part of the regionally used (in western Europe) stage Urgonian.
The Aptian was named after the small city of Apt in the Provence region of France. The original type locality is in the vicinity of Apt. The Aptian was introduced in scientific literature by French palaeontologist Alcide d'Orbigny in 1840.
The base of the Aptian stage is laid at magnetic anomaly M0r. A global reference profile for the base (a GSSP) had in 2009 not yet been appointed. The top of the Aptian (the base of the Albian) is at the first appearance of coccolithophore species Praediscosphaera columnata in the stratigraphic record.
In the Tethys domain, the Aptian contains eight ammonite biozones:
Sometimes the Aptian is subdivided in three substages or subages: Bedoulian (early or lower), Gargasian (middle) and Clansayesian
The Mesozoic Era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the Age of Reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time. The era began in the wake of the Permian-Triassic event, the largest mass extinction in Earth's history, and ended with the Cretaceous–Paleogene extinction event, another mass extinction which is known for having killed off non-avian dinosaurs, as well as other plant and animal species.
Mesozoic means "middle life", deriving from the Greek prefix meso-/μεσο- for "between" and zōon/ζωον meaning "animal" or "living being". It is one of three geologic eras of the Phanerozoic Eon, preceded by the Paleozoic ("ancient life") and succeeded by the Cenozoic ("new life"). The era is subdivided into three major periods: the Triassic, Jurassic, and Cretaceous, which are further subdivided into a number of epochs and stages.
The Mesozoic was a time of significant tectonic, climate and evolutionary activity. The era witnessed the gradual rifting of the supercontinent Pangaea into separate landmasses that would eventually move into their
The Middle Pleistocene, more specifically referred to as the Ionian stage, is a period of geologic time from ca. 781 to 126 thousand years ago.
The base of the Ionian Stage succeeds the Calabrian Stage (the beginning of the Brunhes–Matuyama reversal) and precedes the Tyrrhenian Stage or Upper Pleistocene, which in turn spans from the beginning of the last interglacial (Marine isotopic stage 5) to the base of the Holocene (~10.5 ka).
Although experts are not yet in agreement on how to subdivide the stages of the Pleistocene epoch, a possible international consensus on one subdivision of the Pleistocene epoch called the Ionian Stage exists. The Ionian stage includes all of the European Sicilian Stage and the first part of the Tyrrhenian Stage.
Suitable sections for defining the base of the Ionian Stage are located in southern Italy. During Lower and Middle Pleistocene the Adriatic-Ionian margin was characterized by high sedimentation rates, in response to intense differential tectonic subsidence and massive sedimentary yield. Specifically, candidate sections are the “Montalbano Jonico” Section (Bradanic Trough, Basilicata Region) and the “Valle di Manche Nord” Section (San Mauro
The Upper Paleolithic (or Upper Palaeolithic, Late Stone Age) is the third and last subdivision of the Paleolithic or Old Stone Age as it is understood in Europe, Africa and Asia. Very broadly, it dates to between 50,000 and 10,000 years ago, roughly coinciding with the appearance of behavioral modernity and before the advent of agriculture. The terms "Late Stone Age" and "Upper Paleolithic" refer to the same periods. For historical reasons, "Stone Age" usually refers to the period in Africa, whereas "Upper Paleolithic" is generally used when referring to the period in Europe.
Modern humans (i.e. Homo sapiens) are believed to have emerged about 195,000 years ago in Africa. Though these humans were modern in anatomy, their lifestyle changed very little from their contemporaries, such as Homo erectus and the Neanderthals. They used the same crude stone tools. Archaeologist Richard G. Klein, who has worked extensively on ancient stone tools, describes the stone tool kit of archaic hominids as impossible to categorize. It was as if the Neanderthals made stone tools, and were not much concerned about their final forms. He argues that almost everywhere, whether Asia or Africa or Europe,
In the geologic timescale, the Capitanian is an age or stage of the Permian. It is also the uppermost or latest of three subdivisions of the Guadalupian epoch or series. The Capitanian lasted between 265.8±0.7 and 260.4±0.7 Ma. It was preceded by the Wordian and followed by the Wuchiapingian.
A significant mass extinction event occurred at the end of this stage which may be related to the much larger Permian-Triassic extinction event that followed about 10 million years later.
The Capitanian stage was introduced into scientific literature by George Burr Richardson in 1904. The name comes from the Capitan Reef in the Guadalupe Mountains (Texas, USA). The Capitanian was first used as a stratigraphic subdivision of the Guadalupian in 1961, when both names were still only used regionally in the southern US. The stage was added to the internationally used ISC timescale in 2001.
The base of the Capitanian stage is defined as the place in the stratigraphic record where fossils of conodont species Jinogondolella postserrata first appear. The global reference profile for this stratigraphic boundary is located at Nipple Hill in the southern Guadalupe Mountains of Texas.
The top of the
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma (million years ago). The Albian is preceded by the Aptian and followed by the Cenomanian.
The Albian stage (French Albien, from Alba = the River Aube in France) was first proposed in 1842 by Alcide d'Orbigny.
The base of the Albian is defined as the place in the stratigraphic column where the coccolithophore species Praediscosphaera columnata first appears. A reference profile for the base of the Albian stage (its GSSP) had in 2009 not yet been established.
The top of the Albian stage (the base of the Cenomanian stage and Upper Cretaceous series) is defined as the place where the foram species Rotalipora globotruncanoides first appears in the stratigraphic column.
The Albian is sometimes subdivided in Early/Lower, Middle and Late/Upper subages or substages. In western Europe, especially in the UK, a subdivision in two substages (Vraconian and Gaultian) is more often used.
The following representatives of the Albian stage are worthy of notice:
In the geologic timescale, the Asselian is the earliest geochronologic age or lowermost chronostratigraphic stage of the Permian. It is a subdivision of the Cisuralian epoch or series. The Asselian lasted between 299.0 ± 0.8 and 294.6 ± 0.8 million years ago (Ma). It was preceded by the Gzhelian (the latest or uppermost subdivision in the Carboniferous) and followed by the Sakmarian.
The Asselian stage was introduced into scientific literature in 1954, when the Russian stratigrapher V.E. Ruzhenchev split it from the Artinskian. At that moment the Artinskian still encompassed most of the lower Permian - its current definitions are more restricted. The Asselian is named after the Assel River in the southern Ural Mountains of Kazakhstan.
The base of the Asselian stage is at the same time the base of the Cisuralian series and the Permian system. It is defined as the place in the stratigraphic record where fossils of the conodont Streptognathodus isolatus first appear. The global reference profile for the base (the GSSP or golden spike) is located in the valley of the Aidaralash River, near Aqtöbe in the Ural Mountains of Kazakhstan. The top of the Asselian stage (the base of the
The Chattian is, in the geologic timescale, the youngest of two ages or upper of two stages of the Oligocene epoch/series. It spans the time between 28.4±0.1 and 23.03±0.05 Ma. The Chattian is preceded by the Rupelian and is followed by the Aquitanian (the lowest stage of the Miocene).
The Chattian was introduced by Austrian palaeontologist Theodor Fuchs in 1894. Fuchs named the stage after the Chatti, a Germanic tribe. The original type locality was near the German city of Kassel.
The base of the Chattian is at the extinction of the foram genus Chiloguembelina (which is also the base of foram biozone P21b). An official GSSP for the Chattian stage had not been established yet in 2009.
The top of the Chattian stage (which is the base of the Aquitanian stage, Miocene series and Neogene system) is at the first appearance of foram species Paragloborotalia kugleri, the extinction of calcareous nannoplankton species Reticulofenestra bisecta (which forms the base of nannoplankton biozone NN1), and the base of magnetic chronozone C6Cn.2n.
The Chattian is coeval with regionally used stages or zones like the upper Avernian European mammal zone (it spans the Mammal Paleogene zones 30 through
The Cretaceous ( /krɨˈteɪʃəs/, krə-TAY-shəs), derived from the Latin "creta" (chalk), usually abbreviated K for its German translation Kreide (chalk), is a geologic period and system from circa 145.5 ± 4 to 65.5 ± 0.3 million years (Ma) ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the Cenozoic era. It is the last period of the Mesozoic Era, and, spanning 80 million years, the longest period of the Phanerozoic Eon.
The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels and creating numerous shallow inland seas. These oceans and seas were populated with now extinct marine reptiles, ammonites and rudists, while dinosaurs continued to dominate on land. At the same time, new groups of mammals and birds, as well as flowering plants, appeared. The Cretaceous ended with a large mass extinction, the Cretaceous–Paleogene extinction event, in which many groups, including non-avian dinosaurs, pterosaurs, and large marine reptiles, died out. The end of the Cretaceous is defined by the K–Pg boundary, a geologic signature associated with the mass extinction which lies between the
In the geologic timescale, the Bajocian is an age or stage in the Middle Jurassic. It lasted from approximately 171.6 Ma to around 167.7 Ma (million years ago). The Bajocian age succeeds the Aalenian age and precedes the Bathonian age.
The Bajocian stage takes its name from the Latin name (Bajocae) of the town of Bayeux, in the region of Normandy in France. The stage was named and introduced in scientific literature by French palaeontologist Alcide d'Orbigny in 1842.
The base of the Bajocian stage is defined as the place in the stratigraphic column where fossils of the ammonite genus Hyperlioceras first appear. A global reference profile (a GSSP) for the base is located at Murtinheira, close to Cabo Mondego in Portugal. The top of the Bajocian (the base of the Bathonian) is at the first appearance of ammonite species Parkinsonia convergens.
The Bajocian is often divided into Lower/Early and Upper/Late subages or substages.
In the Tethys domain, the Bajocian contains seven ammonite biozones:
Rhoetosaurus, Ozraptor, Yunnanosaurus, Cetiosauriscus
Simolestes keileni, Maresaurus Coccai
The Frasnian is one of two faunal stages in the Late Devonian period. It lasted from 385.3 ± 2.6 million years ago to 374.5 ± 2.6 million years ago. It was preceded by the Givetian stage and followed by the Famennian stage. It is named after the village of Frasnes-lez-Couvin in Belgium.
Major reef-building was under way during the Frasnian stage, particularly in western Canada and Australia. On land, the first forests were taking shape. In North America, the Antler and Taconic orogenies peaked, which were contemporary with the Bretonic phase of the Variscan orogeny in Europe.
North American subdivisions of the Frasnian include Senecan, Sonyea, Sonyean, and West Falls.
The Irvingtonian North American Land Mammal Age on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 1,800,000 to 240,000 years BP, a period of 1.56 million years. Named after an assemblage of fossils from the Irvington district of Fremont, California, the Irvingtonian is usually considered to overlap the Lower Pleistocene and Middle Pleistocene epochs. The Irvingtonian is preceded by the Blancan and followed by the Rancholabrean NALMA stages.
The Irvingtonian can be further divided into the substages of:
In the geological timescale, the Middle Devonian epoch (from 397.5 ± 2.7 million years ago to 385.3 ± 2.6 million years ago) occurred during the Devonian period, after the end of the Emsian age.
The Middle Devonian epoch is subdivided into two stages: Eifelian and Givetian.
In the middle Devonian the armored jawless fish known as ostracoderms were declining in diversity and instead the jawed fish were thriving and increasing in diversity in both the oceans and freshwater. The shallow, warm, oxygen-depleted waters of Devonian inland lakes, surrounded by primitive plants, provided the environment necessary for certain early fish to develop essential characteristics such as well developed lungs, ability to crawl out of the water and onto the land for short periods of time, possibly in search of food which would be developed by the tetrapods later in the Late Devonian which are descendents of these early fish.
The Buntsandstein (German for 'coloured sandstone') or Bunter sandstone is a lithostratigraphic and allostratigraphic unit (a sequence of rock strata) in the subsurface of large parts of west and central Europe. The Buntsandstein predominantly consists of sandstone layers of the Lower Triassic series and is one of three characteristic Triassic units (together with the Muschelkalk and Keuper that form the Germanic Trias Supergroup.
The Buntsandstein is similar in age, facies and lithology with the Bunter of the British Isles. It is normally lying on top of the Permian Zechstein and below the Muschelkalk. In the past the name Buntsandstein was in Europe also used in a chronostratigraphic sense, as a subdivision of the Triassic system. Among reasons to abandon this use was the discovery that its base lies actually in the latest Permian.
The Buntsandstein was deposited in the Germanic Basin, a large sedimentary basin that was the successor of the smaller Permian Basin and spread across present day Poland, Germany, Denmark, the southern regions of the North Sea and Baltic Sea, the Netherlands and south England. In the late Permian this region had an arid climate and it was covered by
The Burdigalian is, in the geologic timescale, an age or stage in the early Miocene. It spans the time between 20.43 ± 0.05 Ma and 15.97 ± 0.05 Ma (million years ago). Preceded by the Aquitanian, the Burdigalian was the first and longest warming period of the Miocene and is succeeded by the Langhian.
The name Burdigalian comes from Burdigala, the Latin name for the city of Bordeaux, France. The Burdigalian stage was introduced in scientific literature by Charles Depéret in 1892.
The base of the Burdigalian is at the first appearance of foram species Globigerinoides altiaperturus and the top of magnetic chronozone C6An. An official GSSP for the Burdigalian had not yet been assigned in 2009.
The top of the Burdigalian (the base of the Langhian) is defined by the first appearance of foram species Praeorbulina glomerosa and is also coeval with the top of magnetic chronozone C5Cn.1n.
Famous Burdigalian palaeontologic localities include the Turritellenplatte of Ermingen in Germany and the Dominican amber deposits of Hispaniola.
The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic series (or earliest age of the Late Triassic epoch). It lasted from about 228.7 till 216.5 million years ago (Ma). The Carnian is preceded by the Ladinian and is followed by the Norian. Its boundaries are not characterized by major extinctions or biotic turnovers, but a climatic event (known as the Carnian Pluvial Event) occurred during the Carnian and seems to be associated with important extinctions or biotic radiations.
The Carnian was named in 1869 by Mojsisovics. It is unclear if it was named after the Carnic Alps or after the Austrian region of Carinthia (Kärnten in German). The name, however, was first used referring to a part of the Hallstatt Limestone cropping out in Austria.
The base of the Carnian stage is defined as the place in the stratigraphic record where the ammonite species Daxatina canadensis first appears. The global reference profile for the base is located at the Stuores-Wiesen near Badia in the Val Badia in the region of South Tyrol, Italy.
The top of the Carnian (the base of the Norian) is at the bases of the ammonite biozones of Klamathites macrolobatus or Stikinoceras kerri
The Duchesnean North American Stage on the geologic timescale is a North American Land Mammal Age (NALMA), with an age from 42 to 38 million years BP, representing 4 million years. It falls within the Eocene epoch. The Duchesnean is preceded by the Uintan and followed by the Chadronian NALMA.
The Duchesnean falls within the Bartonian age of the geologic timescale.
The Hirnantian is the seventh and final internationally-recognized stage of the Ordovician Period of the Paleozoic Era. It was of short duration, lasting about 1.9 million years, from 445.6 ± 1.5 to 443.7 ± 1.5 Ma (million years ago). The early part of the Hirnantian was characterized by cold temperatures, major glaciation, and a severe drop in sea level. In the latter part of the Hirnantian, temperatures rose, the glaciers melted, and sea level returned to the same or to a slightly higher level than it had been prior to the glaciation.
Most scientists believe that this climatic oscillation caused the major extinction event that took place during this time. In fact, the Hirnantian (also known as the End Ordovician and the Ordovician-Silurian) mass extinction event represents the second largest such event in geologic history. Approximately 85% of marine (sea-dwelling) species died. Only the End Permian mass extinction event was larger. Unlike many smaller extinction events, however, the long-term consequences of the End Ordovician event were relatively small. Following the climatic oscillation, the climate returned to its previous state, and the species that survived soon (within
The Pliocene ( /ˈplaɪ.əsiːn/; archaically Pleiocene) Epoch (symbol PO) is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch. Prior to the 2009 revision of the geologic time scale, which placed the 4 most recent major glaciations entirely within the Pleistocene, the Pliocene also comprised the Gelasian stage, which lasted from 2.588 to 1.805 million years ago.
As with other older geologic periods, the geological strata that define the start and end are well identified but the exact dates of the start and end of the epoch are slightly uncertain. The boundaries defining the onset of the Pliocene are not set at an easily identified worldwide event but rather at regional boundaries between the warmer Miocene and the relatively cooler Pleistocene. The upper boundary was set at the start of the Pleistocene glaciations.
The Pliocene was named by Sir Charles Lyell. The name comes from the Greek words πλεῖον (pleion, "more") and καινός (kainos, "new") and means roughly
The Thanetian is, in the ICS' Geologic timescale, the latest age or uppermost stratigraphic stage of the Paleocene Epoch or series. It spans the time between 58.7±0.2 and 55.8±0.2 Ma. The Thanetian is preceded by the Selandian age and followed by the Ypresian age (part of the Eocene). The Thanetian is sometimes referred to as the Late Paleocene sub-epoch.
The Thanetian was established by Swiss geologist Eugène Renevier in 1873. The Thanetian is named after the area of Kent (southern England) known as the Isle of Thanet. It shares this name with the Thanet Sand Formation, the oldest Cenozoic deposit of the London Basin.
The base of the Thanetian stage is laid at the base of magnetic chronozone C26n. The references profile (Global Boundary Stratotype Section and Point) is in the Zumaia section (43° 18'N, 2° 16'W) at the beach of Itzurun, Pais Vasco, northern Spain.
The top of the Thanetian stage (the base of the Ypresian) is defined at a strong negative anomaly in δC values at the global thermal maximum at the Paleocene-Eocene boundary.
The Thanetian stage is coeval the lower Neustrian European land mammal age (it spans the Mammal Paleogene zone 6 and part of zones 1 through 5.), the
In the geologic timescale the Ypresian is the oldest age or lowest stratigraphic stage of the Eocene. It spans the time between 55.8±0.2 and 48.6±0.2 Ma, is preceded by the Thanetian age (part of the Paleocene) and is followed by the Eocene Lutetian age.
The Ypresian is sometimes included with the Lutetian in an Early Eocene subepoch.
The Ypresian age begins during the throes of the Paleocene–Eocene Thermal Maximum (PETM). The Fur Formation in Denmark and the Messel shales in Germany are from this age.
The Ypresian stage was introduced in scientific literature by Belgian geologist André Hubert Dumont in 1850. The Ypresian is named after Ypres, the French name of the Belgian (Flemish) city of Ieper. The definitions of the original stage were totally different from the modern ones. The Ypresian shares its name with the Belgian Ieper Group (French: Group d'Ypres), which has an Ypresian age.
The base of the Ypresian stage is defined at a strong negative anomaly in δC values at the PETM. The official reference profile (GSSP) for the base of the Ypresian is the Dababiya profile near the Egyptian city of Luxor. Its original type section was located in the vicinity of Ieper.
The top of the
The Coniacian is an age or stage in the geologic timescale. It is a subdivision of the Late Cretaceous epoch or Upper Cretaceous series and spans the time between 89.3 ± 1 Ma and 85.8 ± 0.7 Ma (million years ago). The Coniacian is preceded by the Turonian and followed by the Santonian.
The Coniacian is named after the city of Cognac in the French region of Saintonge. It was first defined by French geologist Henri Coquand in 1857.
The base of the Coniacian stage is at the first appearance of the inoceramid bivalve species Cremnoceramus rotundatus. An official reference profile for the base (a GSSP) had in 2009 not yet been appointed.
The top of the Coniacian (the base of the Santonian stage) is defined by the appearance of the inoceramid bivalve Cladoceramus undulatoplicatus.
The Coniacian overlaps the regional Emscherian stage of Germany, which is roughly coeval with the Coniacian and Santonian stages. In magnetostratigraphy, the Coniacian is part of magnetic chronozone C34, the so called Cretaceous Magnetic Quiet Zone, a relatively long period with normal polarity.
After a maximum of the global sea level during the early Turonian, the Coniacian was characterized by a gradual fall
The Ediacaran Period /ˌiːdiˈækərən/, named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon. Its status as an official geological period was ratified in 2004 by the International Union of Geological Sciences (IUGS), making it the first new geological period declared in 120 years.
Although the Period takes its name from the Ediacara Hills where geologist Reg Sprigg first discovered fossils of the eponymous biota in 1946, the type section is located in the bed of the Enorama Creek within Brachina Gorge in the Flinders Ranges of South Australia, at 31°19′53.8″S 138°38′0.1″E / 31.331611°S 138.633361°E / -31.331611; 138.633361.
The Ediacaran Period overlaps, but is shorter than the Vendian Period, a name that was earlier, in 1952, proposed by Russian geologist and paleontologist Boris Sokolov. The Vendian concept was formed stratigraphically top-down, and the lower boundary of the Cambrian became the upper boundary of the Vendian. Paleontological substantiation of this boundary was worked out
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group (a sequence of rock strata) that has a roughly corresponding age. The Late Triassic spans the time between 235.0 Ma and 201.3 ± 0.2 Ma (million years ago). The Late Triassic is divided into the Carnian, Norian and Rhaetian ages.
Many of the first dinosaurs evolved during the Late Triassic, including Plateosaurus, Coelophysis, and Eoraptor.
Africa shared Pangea's relatively uniform fauna which was dominated by theropods, prosauropods and primitive ornithischians by the close of the Triassic period. Late Triassic fossils are found throughout Africa, but are more common in the south than north. The boundary separating the Triassic and Jurassic marks the advent of an extinction event with global impact, although African strata from this time period have not been thoroughly studied. In the area of Tübingen (Germany), a Triassic-Jurassic bonebed can be found, which is characteristic for this boundary.
The Tiffanian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 60,200,000 to 56,800,000 years BP lasting 3.4 million years. It is usually considered to overlap the Selandian and Thanetian within the Paleocene. The Tiffanian is preceded by the Torrejonian and followed by the Clarkforkian NALMA stages.
The Tiffanian is considered to contain the following substages:
The Triassic is a geologic period and system that extends from about 250 to 200 Ma (million years ago). It is the first period of the Mesozoic Era, and lies between the Permian and Jurassic periods. Both the start and end of the period are marked by major extinction events. The Triassic was named in 1834 by Friedrich Von Alberti, after the three distinct rock layers (tri meaning "three") that are found throughout Germany and northwestern Europe—red beds, capped by chalk, followed by black shales—called the 'Trias.'
The Triassic began in the wake of the Permian–Triassic extinction event, which left the Earth's biosphere impoverished; it would take well into the middle of the period for life to recover its former diversity. Therapsids and archosaurs were the chief terrestrial vertebrates during this time. A specialized subgroup of archosaurs, dinosaurs, first appeared in the mid-Triassic but did not become dominant until the succeeding Jurassic. The first true mammals also evolved during this period, as well as the first flying vertebrates, the pterosaurs. The vast supercontinent of Pangaea existed until the mid-Triassic, after which it began to gradually rift into two separate
In the geologic timescale, the Artinskian is an age or stage of the Permian. It is a subdivision of the Cisuralian epoch or series. The Artinskian lasted between 284.4 ± 0.7 and 275.6 ± 0.7 million years ago (Ma). It was preceded by the Sakmarian and followed by the Kungurian.
The Artinskian is named after the small Russian city of Arti (formerly Artinsk), situated in the southern Ural mountains, about 200 km southwest of Yekaterinburg. The stage was introduced into scientific literature by Alexander Karpinsky in 1874.
The base of the Artinskian stage is defined as the place in the stratigraphic record where fossils of conodont species Sweetognathus whitei and Mesogondolella bissell first appear. As of 2009, there was no agreement yet on a global reference profile (a GSSP) for the base of the Artinskian. The top of the Artinskian (the base of the Kungurian) is defined as the place in the stratigraphic record where fossils of conodonts Neostreptognathodus pnevi and Neostreptognathodus exculptus first appear.
The Bashkirian is in the ICS geologic timescale the lowest stage or oldest age of the Pennsylvanian, the youngest subsystem of the Carboniferous. The Bashkirian age lasted from 318.1 ± 1.3 to 311.7 ± 1.1 Ma, is preceded by the Serpukhovian and is followed by the Moscovian.
The Bashkirian overlaps with the upper part of the Namurian and lower part of the Westphalian stages from regional European stratigraphy. It also overlaps with the North American Morrowan and Atokan stages and the Chinese Luosuan and lower Huashibanian stages.
The Bashkirian was named after the Bashkirs, inhabitants of the republic of Bashkortostan in the southern Ural Mountains (Russia). The stage was introduced by Russian stratigrapher Sofia Semikhatova in 1934.
The base of the Bashkirian is at the first appearance of conodont species Declinognathodus noduliferus. The top of the stage (the base of the Moscovian) is at the first appearance of the conodonts Declinognathodus donetzianus or Idiognathoides postsulcatus, or at the first appearance of fusulinid Aljutovella aljutovica. The GSSP (type location for the base of a stage) for the Bashkirian is in the Battleship Wash Formation at Arrow Canyon, Nevada.
Calabrian is a subdivision of the Pleistocene Epoch of the Geologic time scale. ~1.8 Ma.—781,000 years ago ± 5,000 years, a period of ~1.019 million years.
The end of the stage is defined by the last magnetic pole reversal (781,000 ± 5,000 Ka) and plunge in to an ice age and global drying possibly colder and drier than the late Miocene (Messinian) through early Pliocene (Zanclean) cold period. Originally the Calabrian was a European faunal stage primarily based on mollusk fossils. It has become the second geologic age in the Early Pleistocene. Many of the mammalian faunal assemblages of the Early Pleistocene start in the Gelasian. For example, the Platygonus and other Blancan fauna appear first in the Gelasian.
Because sea shells are much more abundant as fossils, Nineteenth and early Twentieth Century geo-scientists used the plentiful and well-differentiatable Mollusca (mollusks) and Brachiopods to identify stratigraphic boundaries. Thus the Calabrian was originally defined as an assemblage of mollusk fossils, most brachiopods being extinct by then. Efforts were then made to find the best representation of that assemblage in a stratigraphic section. By 1948 scientists used the
Dinantian is the name of a series or epoch from the Lower Carboniferous system in Europe. It can stand for a series of rocks in Europe or the time span in which they were deposited.
The Dinantian is equal to the lower part of the Mississippian series in the international geologic timescale of the ICS. It also correlates with the Avonian, a name proposed by British geologist Arthur Vaughan (1905; p. 264) for certain deposits of the Lower Carboniferous system in the Avon Gorge at Bristol. The Dinantian is named for the Belgian city and province of Dinant where strata of this age occur. The name is still used among European geologists.
The Early Pennsylvanian (also known as the Lower Pennsylvanian) is the first of three subepochs of the Pennsylvanian epoch of the Carboniferous period. It spans the time between 318.1 ± 1.3 Ma and 311.7 ± 1.1 Ma (million years ago). It has one faunal stage, the Bashkirian.
The Gasconadian Stage is the first stage of the Ordovician geologic period in North America and of the Lower Ordovician Canadian Epoch, coming immediately after the Late Cambrian Trempealeauan and preceding the middle Canadian Demingian Stage. The Gasconadian is equivalent to the European Tremedocian and roughly to the Skullrockian of the Ibexian series.
The Gasconadian is named for the Gasconade Formation of Missouri, named in turn for the Gasconade River, and is represented by the Tribes Hill Formation in New York state and by the upper Bliss Fm and the Sierrite Ls of the El Paso Group in southern New Mexico and west Texas.
The Gasconadian is a common term in the paleontological and stratigraphic literature of the previous century, whether used simply for a span of time or for strata laid down during that time.
Recent estimates (ICS and Cosuna) place the beginning of Gasconadian, and Ordovician, anywhere from about 488 to 500 million years ago, with a duration ranging from 9.7 to 10 million years respectively putting the end about 464 m.y.a. Both give estimates of over half the Early Ordovician. 60 percent according th ICS, 2/3 according to Cosuna.
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The Givetian stage is the later stage of the Middle Devonian epoch. It lasted from 391.8 ± 2.7 Ma to 385.3 ± 2.6 Ma.
North American subdivisions of the Givetian include Erian, Senecan, Tioughniogan, Tioughnioga, Cazenovia (pars), Cazenovian (pars), Taghanic, Taghanican, Genesee, and Geneseean.
The stage is named after the French city of Givet.
Lopingian is the third of the three epoches of the Permian. The Lopingian climate was hot and arid. The epoch saw one the largest deserts of all time, in the middle of the supercontinent Pangaea. Monsoons probably prevailed in the coasts or a little further inland. There were probably fewer glaciers than the previous epoch. By the beginning of the epoch saw the extinction of the dominating Dinocephalians therapsids and many remaining pelycosaurs. They were replaced by smaller therapsids, the Gorgonopsians, Therocephalians, and the cynodonts. Other animals, such as the Pareiasaurs replaced the herbivorous dinocephalians, while many animals such as tetrapods, insects, etc., were abundant on land as small to medium sized creatures. In the seas, life was abundant. This all came to a sudden halt, when an unknown mass extinction ended Lopingian, and of course the Paleozoic Era. This was the Permian-Triassic extinction event, the greatest mass extinction of the history of earth. The Cretaceous–Tertiary extinction event pales on comparison with this event. About 90% of all species in the sea died out, as did over 75% of all land species. By the time the extinction stopped, life on land and
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger. This name in the past was also used to indicate the Middle Jurassic epoch itself, but is discouraged by the IUGS, to distinguish between rock units and units of geological time.
During the Middle Jurassic epoch, Pangaea began to separate into Laurasia and Gondwana, and the Atlantic Ocean formed. Tectonic activities are active on eastern Laurasia as the Cimmerian plate continues to collide with Laurasia's southern coast, completely closing the Paleo-Tethys Ocean. A subduction zone on the coast of western North America continues to create the Ancestral Rocky Mountains.
During this time, marine life (including ammonites and bivalves) flourished. Ichthyosaurs, although common, are reduced in diversity; while the top marine predators, the pliosaurs, grew to the size of killer whales and larger (e.g. Pliosaurus, Liopleurodon). Plesiosaurs became common at this time, and metriorhynchid crocodilians first appeared.
New types of dinosaurs evolved on land (including cetiosaurs, brachiosaurs,
The Ordovician ( /ɔrdəˈvɪʃən/) is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago (ICS, 2004). It follows the Cambrian Period and is followed by the Silurian Period. The Ordovician, named after the Celtic tribe of the Ordovices, was defined by Charles Lapworth in 1879 to resolve a dispute between followers of Adam Sedgwick and Roderick Murchison, who were placing the same rock beds in northern Wales into the Cambrian and Silurian periods respectively. Lapworth, recognizing that the fossil fauna in the disputed strata were different from those of either the Cambrian or the Silurian periods, realized that they should be placed in a period of their own. While recognition of the distinct Ordovician Period was slow in the United Kingdom, other areas of the world accepted it quickly. It received international sanction in 1960, when it was adopted as an official period of the Paleozoic Era by the International Geological Congress.
Life continued to flourish during the Ordovician as it did in the Cambrian, although the end of the period was marked by a significant mass extinction. Invertebrates,
The Paleocene (symbol Pε) or Palaeocene, the "early recent", is a geologic epoch that lasted from about 65.5 to 56 million years ago (65.5±0.3 to 55.8±0.2 Ma). It is the first epoch of the Palaeogene Period in the modern Cenozoic Era. As with most other older geologic periods, the strata that define the epoch's beginning and end are well identified but the exact date of the end is uncertain.
The Paleocene Epoch immediately followed the mass extinction event at the end of the Cretaceous, known as the Cretaceous–Paleogene boundary, which marks the demise of non-avian dinosaurs, the giant marine reptiles and much other fauna and flora. The die-off of the dinosaurs left unfilled ecological niches worldwide, and the name "Paleocene" comes from Greek and refers to the "old(er)" (παλαιός, palaios) – "new" (καινός, kainos) fauna that arose during the epoch, before modern mammalian orders emerged in the Eocene.
The K–T boundary that marks the separation between Cretaceous and Paleocene is visible in the geological record of much of the Earth by a discontinuity in the fossil fauna, with high iridium levels. There is also fossil evidence of abrupt changes in flora and fauna. There is some
The Permo-Carboniferous refers to the time period including the latter parts of the Carboniferous and early part of the Permian period. Permo-Carboniferous rocks are in places not differentiated because of the presence of transitional fossils, and also where no conspicuous stratigraphic break is present.
Permo-Carboniferous time, about 300 million years ago, was a period of great glaciation. The widespread distribution of Permo-Carboniferous glacial sediments in South America, Africa, Madagascar, Arabia, India, Antarctica and Australia was one of the major pieces of evidence for the theory of continental drift, and led ultimately to the concept of a super-continent, Pangaea. Glacial activity spanned virtually the whole of Carboniferous and Early Permian time (A.G. Smith, 1997). Toward the end of the Carboniferous, around 290 million years ago, Gondwana, the southern part of Pangaea, was located near the south pole. Glacial centres expanded across the continents, producing glacial tillites and striations in pre-existing rocks. The Permo-Carboniferous ice sheet was so extensive that it would occupy a circle spanning 50 degrees of latitude centered on the pole (A.G. Smith, 1997).