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The Cretaceous
Cretaceous
( /krɪˈteɪʃəs/, kri-TAY-shəs) is a geologic period and system that spans 79 million years from the end of the Jurassic
Jurassic
Period 145 million years ago (mya) to the beginning of the Paleogene Period 66 mya. It is the last period of the Mesozoic
Mesozoic
Era. The Cretaceous
Cretaceous
Period is usually abbreviated K, for its German translation Kreide (chalk). The Cretaceous
Cretaceous
was a period with a relatively warm climate, resulting in high eustatic sea levels that created 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. During this time, new groups of mammals and birds, as well as flowering plants, appeared. The Cretaceous
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
Cretaceous
is defined by the abrupt Cretaceous– Paleogene boundary (K–Pg boundary), a geologic signature associated with the mass extinction which lies between the Mesozoic
Mesozoic
and Cenozoic
Cenozoic
eras.

Contents

1 Geology

1.1 Research history 1.2 Stratigraphic subdivisions 1.3 Rock formations

2 Paleogeography 3 Climate 4 Life

4.1 Flora 4.2 Terrestrial fauna 4.3 Marine fauna 4.4 End- Cretaceous
Cretaceous
extinction event

5 See also 6 References 7 Bibliography 8 External links

Geology[edit] Research history[edit] The Cretaceous
Cretaceous
as a separate period was first defined by Belgian geologist Jean d'Omalius d'Halloy in 1822,[5] using strata in the Paris Basin[6] and named for the extensive beds of chalk (calcium carbonate deposited by the shells of marine invertebrates, principally coccoliths), found in the upper Cretaceous
Cretaceous
of Western Europe.[7] The name Cretaceous
Cretaceous
was derived from Latin
Latin
creta, meaning chalk.[8] Stratigraphic subdivisions[edit] The Cretaceous
Cretaceous
is divided into Early and Late Cretaceous
Late Cretaceous
epochs, or Lower and Upper Cretaceous
Cretaceous
series. In older literature the Cretaceous is sometimes divided into three series: Neocomian (lower/early), Gallic (middle) and Senonian (upper/late). A subdivision in eleven stages, all originating from European stratigraphy, is now used worldwide. In many parts of the world, alternative local subdivisions are still in use. As with other older geologic periods, the rock beds of the Cretaceous are well identified but the exact age of the system's base is uncertain by a few million years. No great extinction or burst of diversity separates the Cretaceous
Cretaceous
from the Jurassic. However, the top of the system is sharply defined, being placed at an iridium-rich layer found worldwide that is believed to be associated with the Chicxulub impact crater, with its boundaries circumscribing parts of the Yucatán Peninsula
Yucatán Peninsula
and into the Gulf of Mexico. This layer has been dated at 66.043 Ma.[9] A 140 Ma age for the Jurassic- Cretaceous
Cretaceous
boundary instead of the usually accepted 145 Ma was proposed in 2014 based on a stratigraphic study of Vaca Muerta
Vaca Muerta
Formation in Neuquén Basin, Argentina.[10] Víctor Ramos, one of the authors of the study proposing the 140 Ma boundary age sees the study as a "first step" toward formally changing the age in the International Union of Geological Sciences.[11] From youngest to oldest, the subdivisions of the Cretaceous
Cretaceous
period are: Late Cretaceous Maastrichtian – (66-72.1 MYA) Campanian – (72.1-83.6 MYA) Santonian – (83.6-86.3 MYA) Coniacian – (86.3-89.8 MYA) Turonian – (89.8-93.9 MYA) Cenomanian – (93.9-100.5 MYA) Early Cretaceous Albian – (100.5-113.0 MYA) Aptian – (113.0-125.0 MYA) Barremian – (125.0-129.4 MYA) Hauterivian – (129.4-132.9 MYA) Valanginian – (132.9-139.8 MYA) Berriasian – (139.8-145.0 MYA) Rock formations[edit]

Drawing of fossil jaws of Mosasaurus
Mosasaurus
hoffmanni, from the Maastrichtian of Dutch Limburg, by Dutch geologist Pieter Harting
Pieter Harting
(1866).

The high sea level and warm climate of the Cretaceous
Cretaceous
meant large areas of the continents were covered by warm, shallow seas, providing habitat for many marine organisms. The Cretaceous
Cretaceous
was named for the extensive chalk deposits of this age in Europe, but in many parts of the world, the deposits from the Cretaceous
Cretaceous
are of marine limestone, a rock type that is formed under warm, shallow marine circumstances. Due to the high sea level there was extensive space for such sedimentation. Because of the relatively young age and great thickness of the system, Cretaceous
Cretaceous
rocks are evident in many areas worldwide. Chalk
Chalk
is a rock type characteristic for (but not restricted to) the Cretaceous. It consists of coccoliths, microscopically small calcite skeletons of coccolithophores, a type of algae that prospered in the Cretaceous
Cretaceous
seas. In northwestern Europe, chalk deposits from the Upper Cretaceous
Cretaceous
are characteristic for the Chalk
Chalk
Group, which forms the white cliffs of Dover on the south coast of England
England
and similar cliffs on the French Normandian coast. The group is found in England, northern France, the low countries, northern Germany, Denmark
Denmark
and in the subsurface of the southern part of the North Sea. Chalk
Chalk
is not easily consolidated and the Chalk
Chalk
Group still consists of loose sediments in many places. The group also has other limestones and arenites. Among the fossils it contains are sea urchins, belemnites, ammonites and sea reptiles such as Mosasaurus. In southern Europe, the Cretaceous
Cretaceous
is usually a marine system consisting of competent limestone beds or incompetent marls. Because the Alpine mountain chains did not yet exist in the Cretaceous, these deposits formed on the southern edge of the European continental shelf, at the margin of the Tethys Ocean. Stagnation of deep sea currents in middle Cretaceous
Cretaceous
times caused anoxic conditions in the sea water leaving the deposited organic matter undecomposed. Half the worlds petroleum reserves were laid down at this time in the anoxic conditions of what would become the Persian Gulf and Gulf of Mexico. In many places around the world, dark anoxic shales were formed during this interval.[12] These shales are an important source rock for oil and gas, for example in the subsurface of the North Sea. Paleogeography[edit] During the Cretaceous, the late-Paleozoic-to-early-Mesozoic supercontinent of Pangaea
Pangaea
completed its tectonic breakup into the present-day continents, although their positions were substantially different at the time. As the Atlantic Ocean
Atlantic Ocean
widened, the convergent-margin mountain building (orogenies) that had begun during the Jurassic
Jurassic
continued in the North American Cordillera, as the Nevadan orogeny
Nevadan orogeny
was followed by the Sevier and Laramide orogenies.

Geography of the Contiguous United States
Contiguous United States
in the late Cretaceous period

Though Gondwana
Gondwana
was still intact in the beginning of the Cretaceous, it broke up as South America, Antarctica
Antarctica
and Australia
Australia
rifted away from Africa
Africa
(though India
India
and Madagascar
Madagascar
remained attached to each other); thus, the South Atlantic and Indian Oceans were newly formed. Such active rifting lifted great undersea mountain chains along the welts, raising eustatic sea levels worldwide. To the north of Africa the Tethys Sea
Tethys Sea
continued to narrow. Broad shallow seas advanced across central North America
North America
(the Western Interior Seaway) and Europe, then receded late in the period, leaving thick marine deposits sandwiched between coal beds. At the peak of the Cretaceous
Cretaceous
transgression, one-third of Earth's present land area was submerged.[13] The Cretaceous
Cretaceous
is justly famous for its chalk; indeed, more chalk formed in the Cretaceous
Cretaceous
than in any other period in the Phanerozoic.[14] Mid-ocean ridge
Mid-ocean ridge
activity—or rather, the circulation of seawater through the enlarged ridges—enriched the oceans in calcium; this made the oceans more saturated, as well as increased the bioavailability of the element for calcareous nanoplankton.[15] These widespread carbonates and other sedimentary deposits make the Cretaceous
Cretaceous
rock record especially fine. Famous formations from North America include the rich marine fossils of Kansas's Smoky Hill Chalk Member and the terrestrial fauna of the late Cretaceous
Cretaceous
Hell Creek Formation. Other important Cretaceous
Cretaceous
exposures occur in Europe
Europe
(e.g., the Weald) and China
China
(the Yixian Formation). In the area that is now India, massive lava beds called the Deccan Traps
Deccan Traps
were erupted in the very late Cretaceous
Cretaceous
and early Paleocene. Climate[edit] The cooling trend of last epoch of the Jurassic
Jurassic
continued into the first age of the Cretaceous. There is evidence that snowfalls were common in the higher latitudes and the tropics became wetter than during the Triassic
Triassic
and Jurassic.[16] Glaciation was however restricted to high-latitude mountains, though seasonal snow may have existed farther from the poles. Rafting by ice of stones into marine environments occurred during much of the Cretaceous
Cretaceous
but evidence of deposition directly from glaciers is limited to the Early Cretaceous of the Eromanga Basin in southern Australia.[17][18] After the end of the first age, however, temperatures increased again, and these conditions were almost constant until the end of the period.[16] The warming may have been due to intense volcanic activity which produced large quantities of carbon dioxide. Between 70–69 Ma and 66–65 Ma, isotopic ratios indicate elevated atmospheric CO2 pressures with levels of 1000–1400 ppmV and mean annual temperatures in west Texas
Texas
between 21 and 23 °C (70-73 °F). Atmospheric CO2 and temperature relations indicate a doubling of pCO2 was accompanied by a ~0.6 °C increase in temperature.[19] The production of large quantities of magma, variously attributed to mantle plumes or to extensional tectonics,[20] further pushed sea levels up, so that large areas of the continental crust were covered with shallow seas. The Tethys Sea
Tethys Sea
connecting the tropical oceans east to west also helped to warm the global climate. Warm-adapted plant fossils are known from localities as far north as Alaska
Alaska
and Greenland, while dinosaur fossils have been found within 15 degrees of the Cretaceous
Cretaceous
south pole.[21] Nonetheless, there is evidence of Antarctic marine glaciation in the Turonian
Turonian
Age.[22] A very gentle temperature gradient from the equator to the poles meant weaker global winds, which drive the ocean currents, resulted in less upwelling and more stagnant oceans than today. This is evidenced by widespread black shale deposition and frequent anoxic events.[23] Sediment cores show that tropical sea surface temperatures may have briefly been as warm as 42 °C (108 °F), 17 °C (31 °F) warmer than at present, and that they averaged around 37 °C (99 °F). Meanwhile, deep ocean temperatures were as much as 15 to 20 °C (27 to 36 °F) warmer than today's.[24][25] Further information: Cool tropics paradox Life[edit]

Although the first representatives of leafy trees and true grasses emerged in the Cretaceous, the flora was still dominated by conifers like Araucaria
Araucaria
(Here: Modern Araucaria
Araucaria
araucana in Chile).

Flora[edit] Flowering plants
Flowering plants
(angiosperms) spread during this period, although they did not become predominant until the Campanian
Campanian
Age near the end of the period. Their evolution was aided by the appearance of bees; in fact angiosperms and insects are a good example of coevolution. The first representatives of many leafy trees, including figs, planes and magnolias, appeared in the Cretaceous. At the same time, some earlier Mesozoic
Mesozoic
gymnosperms continued to thrive; pehuéns (monkey puzzle trees, Araucaria) and other conifers being notably plentiful and widespread. Some fern orders such as Gleicheniales[26] appeared as early in the fossil record as the Cretaceous, and achieved an early broad distribution. Gymnosperm
Gymnosperm
taxa like Bennettitales
Bennettitales
and hirmerellan conifers died out before the end of the period.[27] Terrestrial fauna[edit] On land, mammals were generally small sized, but a very relevant component of the fauna, with cimolodont multituberculates outnumbering dinosaurs in some sites.[28] Neither true marsupials nor placentals existed until the very end,[29] but a variety of non-marsupial metatherians and non-placental eutherians had already begun to diversify greatly, ranging as carnivores (Deltatheroida), aquatic foragers (Stagodontidae) and herbivores (Schowalteria, Zhelestidae). Various "archaic" groups like eutriconodonts were common in the Early Cretaceous, but by the Late Cretaceous
Late Cretaceous
northern mammalian faunas were dominated by multituberculates and therians, with dryolestoids dominating South America. The apex predators were archosaurian reptiles, especially dinosaurs, which were at their most diverse stage. Pterosaurs were common in the early and middle Cretaceous, but as the Cretaceous
Cretaceous
proceeded they declined for poorly understood reasons (once thought to be due to competition with early birds, but now it is understood avian adaptive radiation is not consistent with pterosaur decline[30]), and by the end of the period only two highly specialized families remained. The Liaoning
Liaoning
lagerstätte (Chaomidianzi formation) in China
China
is a treasure chest of preserved remains of numerous types of small dinosaurs, birds and mammals, that provides a glimpse of life in the Early Cretaceous. The coelurosaur dinosaurs found there represent types of the group Maniraptora, which is transitional between dinosaurs and birds, and are notable for the presence of hair-like feathers. Insects diversified during the Cretaceous, and the oldest known ants, termites and some lepidopterans, akin to butterflies and moths, appeared. Aphids, grasshoppers and gall wasps appeared.[31]

Tyrannosaurus
Tyrannosaurus
rex, one of the largest land predators of all time, lived during the late Cretaceous.

Up to 2 m long and 0.5 m high at the hip, Velociraptor
Velociraptor
was feathered and roamed the late Cretaceous.

Triceratops, one of the most recognizable genera of the Cretaceous

Liaoconodon, an example of an aquatic mammal

A pterosaur, Anhanguera piscator

Confuciusornis, a genus of crow-sized birds from the Early Cretaceous

Ichthyornis
Ichthyornis
was a toothed seabird-like ornithuran from the late Cretaceous
Cretaceous
period

Marine fauna[edit] In the seas, rays, modern sharks and teleosts became common.[32] Marine reptiles included ichthyosaurs in the early and mid-Cretaceous (becoming extinct during the late Cretaceous
Cretaceous
Cenomanian-Turonian anoxic event), plesiosaurs throughout the entire period, and mosasaurs appearing in the Late Cretaceous. Baculites, an ammonite genus with a straight shell, flourished in the seas along with reef-building rudist clams. The Hesperornithiformes were flightless, marine diving birds that swam like grebes. Globotruncanid Foraminifera
Foraminifera
and echinoderms such as sea urchins and starfish (sea stars) thrived. The first radiation of the diatoms (generally siliceous shelled, rather than calcareous) in the oceans occurred during the Cretaceous; freshwater diatoms did not appear until the Miocene.[31] The Cretaceous
Cretaceous
was also an important interval in the evolution of bioerosion, the production of borings and scrapings in rocks, hardgrounds and shells.

A scene from the early Cretaceous: a Woolungasaurus
Woolungasaurus
is attacked by a Kronosaurus.

Tylosaurus
Tylosaurus
was a large mosasaur, carnivorous marine reptiles that emerged in the late Cretaceous.

Strong-swimming and toothed predatory waterbird Hesperornis
Hesperornis
roamed late Cretacean oceans.

The ammonite Discoscaphites
Discoscaphites
iris, Owl Creek Formation (Upper Cretaceous), Ripley, Mississippi

A plate with Nematonotus
Nematonotus
sp., Pseudostacus sp. and a partial Dercetis triqueter, found in Hakel, Lebanon

End- Cretaceous
Cretaceous
extinction event[edit]

The impact of a meteorite or comet is today widely accepted as the main reason for the Cretaceous– Paleogene extinction event.

Main article: Cretaceous– Paleogene extinction event The impact of a large body with the Earth may have been the punctuation mark at the end of a progressive decline in biodiversity during the Maastrichtian
Maastrichtian
Age of the Cretaceous
Cretaceous
Period. The result was the extinction of three-quarters of Earth's plant and animal species. The impact created the sharp break known as K–Pg boundary
K–Pg boundary
(formerly known as the K–T boundary). Earth's biodiversity required substantial time to recover from this event, despite the probable existence of an abundance of vacant ecological niches.[33] Despite the severity of K-Pg extinction event, there was significant variability in the rate of extinction between and within different clades. Species which depended on photosynthesis declined or became extinct as atmospheric particles blocked solar energy. As is the case today, photosynthesizing organisms, such as phytoplankton and land plants, formed the primary part of the food chain in the late Cretaceous, and all else that depended on them suffered as well. Herbivorous animals, which depended on plants and plankton as their food, died out as their food sources became scarce; consequently, the top predators such as Tyrannosaurus
Tyrannosaurus
rex also perished.[34] Yet only three major groups of tetrapods disappeared completely; the non-avian dinosaurs, the plesiosaurs and the pterosaurs. The other Cretaceous groups that did not survive into the Cenozoic
Cenozoic
era, the ichthyosaurs and last remaining temnospondyls and non-mammalian cynodonts were already extinct millions of years before the event occurred.[citation needed] Coccolithophorids
Coccolithophorids
and molluscs, including ammonites, rudists, freshwater snails and mussels, as well as organisms whose food chain included these shell builders, became extinct or suffered heavy losses. For example, it is thought that ammonites were the principal food of mosasaurs, a group of giant marine reptiles that became extinct at the boundary.[35] Omnivores, insectivores and carrion-eaters survived the extinction event, perhaps because of the increased availability of their food sources. At the end of the Cretaceous
Cretaceous
there seem to have been no purely herbivorous or carnivorous mammals. Mammals and birds which survived the extinction fed on insects, larvae, worms and snails, which in turn fed on dead plant and animal matter. Scientists theorise that these organisms survived the collapse of plant-based food chains because they fed on detritus.[36][33][37] In stream communities, few groups of animals became extinct. Stream communities rely less on food from living plants and more on detritus that washes in from land. This particular ecological niche buffered them from extinction.[38] Similar, but more complex patterns have been found in the oceans. Extinction
Extinction
was more severe among animals living in the water column, than among animals living on or in the sea floor. Animals in the water column are almost entirely dependent on primary production from living phytoplankton, while animals living on or in the ocean floor feed on detritus or can switch to detritus feeding.[33] The largest air-breathing survivors of the event, crocodilians and champsosaurs, were semi-aquatic and had access to detritus. Modern crocodilians can live as scavengers and can survive for months without food and go into hibernation when conditions are unfavourable, and their young are small, grow slowly, and feed largely on invertebrates and dead organisms or fragments of organisms for their first few years. These characteristics have been linked to crocodilian survival at the end of the Cretaceous.[36]

Numerous borings in a Cretaceous
Cretaceous
cobble, Faringdon, England; these are excellent examples of fossil bioerosion.

Cretaceous
Cretaceous
hardground from Texas
Texas
with encrusting oysters and borings. The scale bar is 10 mm.

Rudist
Rudist
bivalves from the Cretaceous
Cretaceous
of the Omani Mountains, United Arab Emirates. Scale bar is 10 mm.

Inoceramus
Inoceramus
from the Cretaceous
Cretaceous
of South Dakota.

See also[edit]

Cretaceous
Cretaceous
portal Paleontology portal

Chalk
Chalk
Formation Cretaceous
Cretaceous
Thermal Maximum List of fossil sites
List of fossil sites
(with link directory) South Polar dinosaurs Western Interior Seaway

References[edit]

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oceanic anoxic events: Nitrogen and carbon isotopic evidence from sedimentary porphyrin". Organic Geochemistry. 39 (5): 532–549. doi:10.1016/j.orggeochem.2007.11.010. Retrieved 2008-05-10.  Neal L Larson, Steven D Jorgensen, Robert A Farrar and Peter L Larson. Ammonites
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and the other Cephalopods of the Pierre Seaway. Geoscience Press, 1997. Ogg, Jim; June, 2004, Overview of Global Boundary Stratotype Sections and Points (GSSP's) https://web.archive.org/web/20060716071827/http://www.stratigraphy.org/gssp.htm Accessed April 30, 2006. Ovechkina, M.N.; Alekseev, A.S. (2005). "Quantitative changes of calcareous nannoflora in the Saratov region (Russian Platform) during the late Maastrichtian
Maastrichtian
warming event" (PDF). Journal of Iberian Geology. 31 (1): 149–165. Archived from the original (PDF) on August 24, 2006.  Rasnitsyn, A.P. and Quicke, D.L.J. (2002). History of Insects. Kluwer Academic Publishers. ISBN 1-4020-0026-X. CS1 maint: Multiple names: authors list (link) —detailed coverage of various aspects of the evolutionary history of the insects. Skinner, Brian J., and Stephen C. Porter. The Dynamic Earth: An Introduction to Physical Geology. 3rd ed. New York: John Wiley & Sons, Inc., 1995. ISBN 0-471-60618-9 Stanley, Steven M. Earth System History. New York: W.H. Freeman and Company, 1999. ISBN 0-7167-2882-6 Taylor, P. D.; Wilson, M. A. (2003). "Palaeoecology and evolution of marine hard substrate communities". Earth-Science Reviews. 62: 1–103. Bibcode:2003ESRv...62....1T. doi:10.1016/S0012-8252(02)00131-9. 

External links[edit]

Wikimedia Commons has media related to Cretaceous.

Look up cretaceous in Wiktionary, the free dictionary.

UCMP Berkeley Cretaceous
Cretaceous
page Bioerosion
Bioerosion
website at The College of Wooster Cretaceous
Cretaceous
Microfossils: 180+ images of Foraminifera  " Cretaceous
Cretaceous
System". Encyclopædia Britannica. 7 (11th ed.). 1911. pp. 414–418. 

v t e

Cretaceous
Cretaceous
Period

Lower/Early Cretaceous Upper/Late Cretaceous

Berriasian Valanginian Hauterivian Barremian Aptian Albian

Cenomanian Turonian Coniacian Santonian Campanian Maastrichtian

v t e

Geologic history of Earth

Cenozoic
Cenozoic
era¹ (present–66.0 Mya)

Quaternary
Quaternary
(present–2.588 Mya)

Holocene
Holocene
(present–11.784 kya) Pleistocene
Pleistocene
(11.784 kya–2.588 Mya)

Neogene
Neogene
(2.588–23.03 Mya)

Pliocene
Pliocene
(2.588–5.333 Mya) Miocene
Miocene
(5.333–23.03 Mya)

Paleogene (23.03–66.0 Mya)

Oligocene
Oligocene
(23.03–33.9 Mya) Eocene
Eocene
(33.9–56.0 Mya) Paleocene
Paleocene
(56.0–66.0 Mya)

Mesozoic
Mesozoic
era¹ (66.0–252.17 Mya)

Cretaceous
Cretaceous
(66.0–145.0 Mya)

Late (66.0–100.5 Mya) Early (100.5–145.0 Mya)

Jurassic
Jurassic
(145.0–201.3 Mya)

Late (145.0–163.5 Mya) Middle (163.5–174.1 Mya) Early (174.1–201.3 Mya)

Triassic
Triassic
(201.3–252.17 Mya)

Late (201.3–237 Mya) Middle (237–247.2 Mya) Early (247.2–252.17 Mya)

Paleozoic
Paleozoic
era¹ (252.17–541.0 Mya)

Permian
Permian
(252.17–298.9 Mya)

Lopingian
Lopingian
(252.17–259.8 Mya) Guadalupian
Guadalupian
(259.8–272.3 Mya) Cisuralian
Cisuralian
(272.3–298.9 Mya)

Carboniferous
Carboniferous
(298.9–358.9 Mya)

Pennsylvanian (298.9–323.2 Mya) Mississippian (323.2–358.9 Mya)

Devonian
Devonian
(358.9–419.2 Mya)

Late (358.9–382.7 Mya) Middle (382.7–393.3 Mya) Early (393.3–419.2 Mya)

Silurian
Silurian
(419.2–443.8 Mya)

Pridoli (419.2–423.0 Mya) Ludlow (423.0–427.4 Mya) Wenlock (427.4–433.4 Mya) Llandovery (433.4–443.8 Mya)

Ordovician
Ordovician
(443.8–485.4 Mya)

Late (443.8–458.4 Mya) Middle (458.4–470.0 Mya) Early (470.0–485.4 Mya)

Cambrian
Cambrian
(485.4–541.0 Mya)

Furongian (485.4–497 Mya) Series 3 (497–509 Mya) Series 2 (509–521 Mya) Terreneuvian
Terreneuvian
(521–541.0 Mya)

Proterozoic
Proterozoic
eon² (541.0 Mya–2.5 Gya)

Neoproterozoic era (541.0 Mya–1 Gya)

Ediacaran
Ediacaran
(541.0-~635 Mya) Cryogenian (~635-~720 Mya) Tonian (~720 Mya-1 Gya)

Mesoproterozoic era (1–1.6 Gya)

Stenian (1-1.2 Gya) Ectasian (1.2-1.4 Gya) Calymmian (1.4-1.6 Gya)

Paleoproterozoic era (1.6–2.5 Gya)

Statherian (1.6-1.8 Gya) Orosirian
Orosirian
(1.8-2.05 Gya) Rhyacian (2.05-2.3 Gya) Siderian
Siderian
(2.3-2.5 Gya)

Archean
Archean
eon² (2.5–4 Gya)

Eras

Neoarchean (2.5–2.8 Gya) Mesoarchean (2.8–3.2 Gya) Paleoarchean
Paleoarchean
(3.2–3.6 Gya) Eoarchean
Eoarchean
(3.6–4 Gya)

Hadean
Hadean
eon² (4–4.6 Gya)

 

 

kya = thousands years ago. Mya = millions years ago. Gya = billions years ago.¹ = Phanerozoic
Phanerozoic
eon. ² = Precambrian
Precambrian
supereon. Source: (2015/01). International Commission on Stratigraphy. Retrieved 13 July 2015. Divisions of Geologic Time—Major Chronostratigraphic and Geochronologic Units USGS Retrieved 10 March 2013.

Authority control

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