Geologic time scale

The geologic time scale helps us understand Earth's long history by breaking it into time intervals. Scientists study layers of rock and use special dating methods, like radiometric dating, to find out when events happened long ago. This tool is very useful for Earth scientists, such as geologists and paleontologists, because it helps them describe when things happened and how they are connected.

By looking at rocks and fossils, scientists made a timeline that shows the big periods and events in Earth's history. This timeline is managed by groups like the International Commission on Stratigraphy, which makes sure the divisions are correct and agreed upon around the world. The geologic time scale helps us see how Earth has changed over billions of years, from the very start until today.

Principles

The geologic time scale helps us understand Earth's long history, which is about 4.54 billion years. It organizes rocks by when they formed, looking at changes in rock layers that match big events in Earth's past. This uses two main ideas:

Chronostratigraphy studies how rocks fit together in order. It uses simple rules, like the fact that older rocks are usually found below younger rocks.

Geochronology dates rocks using science, often with radiometric dating. Together, these help scientists match rock layers from different places and understand when Earth's events happened.

Divisions of geologic time

Geologists use the geologic time scale to sort Earth's history into clear time periods. This scale helps scientists learn about the order of events that shaped our planet. The scale is divided into large parts called eons. These eons are split into smaller parts like eras, periods, epochs, and ages. For example, we live in the Phanerozoic eon, the Cenozoic era, and the Quaternary period.

Each part of the scale has a specific number of years. Scientists use words like Ma (million years) and Ga (billion years) to talk about these time periods. The scale helps us connect rocks from different places to the same time, giving us a better view of Earth's long history.

Formal, hierarchical units of the geologic time scale (largest to smallest)
Chronostratigraphic unit (strata)	Geochronologic unit (time)	Time span
Eonothem	Eon	Several hundred million years to two billion years
Erathem	Era	Tens to hundreds of millions of years
System	Period	Millions of years to tens of millions of years
Series	Epoch	Hundreds of thousands of years to tens of millions of years
Subseries	Subepoch	Thousands of years to millions of years
Stage	Age	Thousands of years to millions of years

Naming of geologic time

The names of time periods in Earth's history help scientists understand important changes. For example, the Paleozoic means "old life," the Mesozoic means "middle life," and the Cenozoic means "new life." Some names come from where the rocks were first found, like the Permian or the Ordovician. Others describe the type of rocks, such as the Cretaceous.

Before the Cambrian period, the time is often called the Precambrian. Scientists like to use local place names when they create new time period names.

History of the geologic time scale

The modern geologic time scale was made in 1911 by Arthur Holmes. He was inspired by James Hutton, a Scottish geologist who believed Earth's changes happen slowly over long periods. People have thought about rocks and time for a very long time, going back to ancient philosophers in Ancient Greece.

Sketch of the Succession of Strata and their Relative Altitudes (William Smith)

Early thinkers like Xenophanes of Colophon noticed seashells in rocks far from the sea. They thought the sea had moved over time. Later, Shen Kuo, a Chinese scientist, and Avicenna, a Persian scholar, also studied how rocks form layers. These ideas helped scientists learn that Earth is very old.

Leonardo da Vinci studied rocks and fossils. He thought they were left by the sea, not by big floods. In the 1800s, William Smith, called the "Father of Geology," studied rock layers and fossils. He found that each layer had unique fossils that could help match layers from different places.

Nicolas Steno made four important rules to understand rock layers. These rules help scientists learn the order of layers and what happened long ago. Over time, scientists learned that rock layers can change shape, and layers from the same time can look different in different places.

Today, scientists use special methods to date rocks very accurately. These methods help us learn how old Earth is and what happened during different times in its history.

Table of geologic time

The table of geologic time shows the big events and features that help us learn about Earth's long history. It lists the newest times at the top and the oldest at the bottom. But the height of each part in the table does not show how long each time really lasted. The Phanerozoic Eon, which includes the time we live in now, looks bigger in the table than it really is. It covers about 538.8 million years, which is only a small part of Earth's whole history. The other three older eons together cover about 4,028.2 million years, most of Earth's history. This happens because we know more about recent times than about the very early times.

The table follows the official rules, names, and colors set by the International Commission on Stratigraphy. These rules help scientists all over the world talk about Earth's history in the same way.

Eonothem/ Eon	Erathem/ Era	System/ Period	Series/ Epoch	Stage/ Age	Major events	Start, million years ago
Phanerozoic	Cenozoic	Quaternary	Holocene	Meghalayan	4.2 ka cool period, dry climate leads to decline of agriculture-related civilisations in Egypt, Mesopotamia and India. Medieval Warm Period (about 900 - 1350 CE) and Little Ice Age (about 1400 to 1900 CE). Rapidly warming climate as CO₂ added to atmosphere from burning fossil fuels.	0.0042 ^*
				Northgrippian	8.2 ka cool period, followed by warming climate with melting ice raising sea levels. Doggerland and Sundaland flooded.	0.0082 ^*
				Greenlandian	Younger Dryas and Last Glacial Period end. Rise of agriculture. Extinction of Pleistocene megafauna.	0.0117 ^*
			Pleistocene	Upper/Late ('Tarantian')	Eemian Interglacial Stage followed by the Last Glacial Period. After Last Glacial Maximum (about 25 – 15 ka) climate begins to warm. Younger Dryas final cold period of ice age. Toba supervolcano eruption. Homo sapiens spread across the globe. Homo floresiensis live on island of Flores. Homo neanderthalensis go extinct.	0.129
				Chibanian	Brunhes–Matuyama geomagnetic reversal event. Homo heidelbergensis evolves in Africa and spreads to Europe. Homo neanderthalensis appear in western Eurasia. Homo sapiens evolve in Africa. Homo erectus and Homo heidelbergensis die out.	0.774 ^*
				Calabrian	Mid Pleistocene transition: glacial/interglacial frequency slows to every 100,000 years. Glacial periods now long enough for continental ice-sheets beyond polar regions. Chimpanzees and bonobos diverge. Homo erectus spreads through Eurasia. Homo habilis goes extinct.	1.8 ^*
				Gelasian	Start of Pleistocene Ice Age: 40,000 year cycles of glacials/interglacials with ice cap growth and retreat, and sea level falls and rises. Rise of Pleistocene megafauna. Homo habilis and Homo erectus evolve in Africa.	2.58 ^*
		Neogene	Pliocene	Piacenzian	Isthmus of Panama land bridge forms between North and South America blocking equatorial ocean currents between Atlantic and Pacific oceans. Gulf Stream develops as Atlantic waters divert northward. Global temperatures warm melting polar ice caps and sea levels rise flooding continental margins. Temperatures drop at 2.7 Ma and the Pleistocene Ice Age begins. First modern big cats and modern horses. Tortoises and finches arrive in the Galapagos. Earliest humans appear.	3.6 ^*
			Pliocene	Zanclean	Straits of Gibraltar form as Atlantic waters flood the Mediterranean Sea basin (Zanclean flood). Global climate continues to cool. Asian elephants appear. Hominins Ardipithecus, Australopithecus and Paranthropus evolve.	5.333 ^*
			Miocene	Messinian	Connection between Mediterranean Sea and Atlantic is blocked, resulting in Messinian salinity crisis with evaporites accumulating across Mediterranean as its waters dry up. Collision of Banda Arc with Australia and Timor begins. Global climate cools and permanent ice cap forms in Arctic. Sea levels drop as ice sheets grow. Spread of C4 grasses result in extinction of many herbivoress. Sea snakes evolve. Gorilla-human-chimpanzee lineages split, then chimpanzees and humans diverge. Earliest hominid Sahelanthropus.	7.246 ^*
				Tortonian		11.63 ^*
				Serravallian	Australia begins to collide with Southeast Asia, blocking equatorial circulation between western Pacific and Indian Oceans. Antarctic ice cap shrinks as global temperatures warm (Middle Miocene climatic optimum). Last creodonts (early predatory mammals) become extinct. Megalodon (giant shark) evolves.	13.82 ^*
				Langhian		15.98 ^*
				Burdigalian	The Tian Shan and Altai mountains, Central Asia, form (Himalayan orogeny). Columbia River Basalt large igneous province (LIP) eruptions above rising Yellowstone hotspot, North America. Climate continues to cool. Compositae (herbaceous plants) appear and rapidly diversify, triggering evolutionary radiations in rodents, snakes (first vipers appear) and songbirds. First gibbons and orangutans. First modern dolphins.	20.45
				Aquitanian		23.04 ^*
		Paleogene	Oligocene	Chattian	North America and Eurasia plate boundary established along Mid-Atlantic Ridge. Central American volcanic arc begins to collide with South America. East African LIP eruptions begin as Afar mantle plume rises. Late Cenozoic Ice Age begins. Rapid growth of the Antarctic ice cap produces major drop in global sea levels. Grasslands and prairies thrive as climate dries. Paraceratherium largest ever land mammal flourishes. First felids (cats), mustelids (e.g. weasels, otters, badgers), and pinnipeds (seals, sea lions and walruses). Whales split into toothed and filter feeders. Multituberculates (rat-like early mammals) go extinct.	27.3 ^*
			Oligocene	Rupelian		33.9 ^*
			Eocene	Priabonian	Subduction in the Mediterranean leads to Tell-Rif-Betic, Dinarides, Hellenides and Taurides (Alpine) orogenies. Eurekan orogeny, Greenland. Zagros orogeny as Arabia and Eurasia collide. Laramide orogeny ends. Gulf of Aden forms between Africa and Asia. Cooling climate with brief warm period. End Eocene Australia and South America move away from Antarctica opening Drake and Tasmanian passages. Antarctic Circumpolar current forms. Rapid drop in global temperatures. Ice sheets on Antarctica. Canids (wolves and foxes), Catarrhine primates (old world monkeys and apes), and raptors evolve. Basilosaurus is first fully aquatic whale.	37.71 ^*
				Bartonian		41.03
				Lutetian		48.07 ^*
				Ypresian	Greenland separates from Eurasia and Eurasian Basin opens in Arctic. Greater India collides with southern Eurasia, beginning Himalayan orogeny. North Atlantic LIP eruptions continue. Major reorganisation of plate motions across Pacific region initiates Izu-Bonin-Mariana and Tonga-Kermadec subduction zones. Greenhouse temperatures continue from Paleocene-Eocene Thermal Maximum (PETM) as climate affected by North Atlantic LIP eruptions, but global cooling begins from about 50 Ma with changing paleogeography and oceanography conditions. Angiosperms (flowering plants) evolve larger fruits. First songbirds, parrots and woodpeckers. Primates divide into strepsirrhines (lemurs and lorises) and haplorhines (tarsiers and anthropoids). Artiodactyls (even-toed ungulates) appear and split into Cetruminantia (ruminants, whales and dolphins), Suina (pigs), and Tylopoda (camels and relatives). First Carnivora (meat-eating mammals). Mice, rats, bats and tapirs appear. Eohippus earliest member of horse family. Marsupials reach Australia.	56 ^*
			Paleocene	Thanetian	Alpine orogeny develops as Neotethys closes and Africa begins collision with Eurasia. Pyrenean and Laramide orogenies continue. India drifts rapidly northwards. North Atlantic LIP eruptions start as Proto-Icelandic mantle plume rises. Subduction zones form along margins of Caribbean plate. Bering Straits land bridge present during low sea level periods. Chicxulub impact causes "impact winter", then climate warms with final eruption of the Deccan Traps before cool, dry conditions re-established. Rapid rise in global temperatures at onset of PETM due to North Atlantic LIP eruptions. End-Cretaceous mass extinction about 75% of plant and animal species go extinct, including ammonoids, rudist molluscs, non-avian dinosaurs, plesiosaurs, mosasaurs and pterosaurs. Mammals evolve quickly filling vacant ecological niches, modern groups of birds diversify and angiosperms become dominant form of plant life. First earthworms and land turtles. Phorusrhacidae (terror birds) and creodonts (early predatory mammals) evolve. Perissodactyls (odd-toed ungulates) appear and diversify. First primates, proboscideans (elephants), Xenartha (sloths, anteaters and armadillos) and rodents.	59.24 ^*
				Selandian		61.66 ^*
				Danian		66 ^*
	Mesozoic	Cretaceous	Upper/Late	Maastrichtian	Pangaea continues to fragment. Africa and South America separate as seafloor spreading established in South Atlantic. India and Australia move away from Antarctica, and India separates from Madagascar. Central Atlantic propagates north. \|Pyrenean orogeny begins as Iberia rotates relative to Eurasia. Africa moves northwards. Sevier and Laramide orogenies, western North America. LIP eruptions include: Ontong Java-Nui; Kerguelen; High Arctic and Deccan Traps. Highest sea levels in the Phanerozoic, shallow seas extend across large areas of the continents. Greenhouse climate global average temperature peaks c. 28 °C in the Cenomanian-Turonian. Tropical plants and dinosaurs on Antarctica and above Arctic Circle. Oceanic anoxic events (OAEs) result in widespread deposition of organic-rich black shales. Calcareous foraminifera and coccolithophores flourish forming massive chalk deposits. Teleost (bony fish) radiate. Predators grow large: plesiosaurs and mosasaurs in the sea; carcharodontosaurs and tyrannosaurs on land. Modern lobsters, crabs, shrimps and crocodiles appear. First bees, termites, ants, fleas, mantids and snakes. Angiosperms (flowering plants) proliferate and develop symbiotic relationships with insects. First grasses. Woody angiosperms evolve including rose, magnolia and sycamore families. First marsupials and monotremes. End of the Cretaceous is marked by the Chicxulub impact event and the Cretaceous-Paleogene mass extinction.	72.2 ± 0.2 ^*
				Campanian		83.6 ± 0.2 ^*
				Santonian		85.7 ± 0.2 ^*
				Coniacian		89.8 ± 0.3 ^*
				Turonian		93.9 ± 0.2 ^*
				Cenomanian		100.5 ± 0.1 ^*
			Lower/Early	Albian		~113.2 ± 0.3 ^*
				Aptian		~121.4 ± 0.6
				Barremian		~125.77 ^*
				Hauterivian		~132.6 ± 0.6 ^*
				Valanginian		~137.05 ± 0.2 ^*
				Berriasian		~143.1 ± 0.6
		Jurassic	Upper/Late	Tithonian	Seafloor spreading in the Central Atlantic between North America and Africa-South America begins break up of Pangaea. Rifting continues in northern Atlantic and Caribbean. Gondwana splits into East and West Gondwana as Somali and Mozambique basins open. Pacific plate forms in central Panthalassa. Cimmerian and Indosinian orogenies continue. Start of Andean tectonic cycle, South America. Nevadan orogeny, North America. Mongol-Okhotsk Ocean closes forming Verkhoyansk-Kolyma mountain belt, Siberia. Neotethys narrows. Greenhouse climate with warmer and cooler periods. Arid conditions across equatorial and subtropical regions; coal and bauxite deposits in wetter temperate belts. Emplacement of Karoo-Ferrar LIP leads to global warming and the widespread Toarcian oceanic anoxic event. Rise in global sea levels. Change from aragonite to calcite seas. First large reefs. Phytoplankton and dinoflagellates diversify. First coccolithophores. Ammonoids and bellomnoids proliferate. Major radiation of sharks. Vieraella earliest true frog. First modern turtles. Cycads dominant forest flora. Also ferns, conifers and ginkgos. Dinosaurs rise to dominance, mammals remain small. First Ornithischia (e.g. stegasaurs and ceratopsians). Sauropods evolve into giants, including brachiosaurs, titanosaurs, and diplodocids. First ceratosaurs, megalosaurs, allosaurs, and coelurosaurs therapods. Coelurosaurs, many with feathers, include early tyrannosaurs and maniraptorans (ancestors of birds). First pterodactyloids.	149.2 ± 0.7
				Kimmeridgian		154.8 ± 0.8 ^*
				Oxfordian		161.5 ± 1.0
			Middle	Callovian		165.3 ± 1.1
				Bathonian		168.2 ± 1.2 ^*
				Bajocian		170.9 ± 0.8 ^*
				Aalenian		174.7 ± 0.8 ^*
			Lower/Early	Toarcian		184.2 ± 0.3 ^*
				Pliensbachian		192.9 ± 0.3 ^*
				Sinemurian		199.5 ± 0.3 ^*
				Hettangian		201.4 ± 0.2 ^*
		Triassic	Upper/Late	Rhaetian	Pangaea forms an arc extending from almost pole to pole. Siberian Traps eruptions wane, but hot house climate continues. Cimmerian terranes collide with Eurasia: Indosinian orogeny in east; Cimmerian orogeny in west. Sonoma (western Laurussia), and Hunter-Bowen (Australia) orogenies continue. Late Triassic, emplacement of the Central Atlantic magmatic province (CAMP) followed by seafloor spreading marks start of Pangaea break up. Archosaurs divide into pseudosuchia (crocodiles), and ornithodirans (dinosaurs and pterosaurs). Mammaliaformes evolve from cynodonts. Evidence of endothermy (warm-bloodedness) in dinosaurs and mammals. First teleosts (modern ray-finned fish). Ichthyosaurs, and sauropterygians plesiosaurs, nothosaurs, placodonts) appear. First scleractinian (hard coral) reefs. First wasps and stick insects. Late Triassic eruptions of Wrangellia LIP raises temperatures, intensifies Pangaea monsoons and increases rainfall (Carnian pluvial episode). Bennettitales, modern ferns and conifers appear. First Lepidoptera (moths and butterflies). Modern groups of phytoplankton appear. Manicouagan bolide impact reduces global temperatures, before CAMP eruptions increases them and triggers Triassic-Jurassic mass extinction. Major loss of reef ecosystems, reduction in marine genera, conodonts die out. Major changes in terrestrial flora. Loss of vertebrate genera, including non-mammalian therapsids. Crocodylomorphs only pseudosuchians to survive.	~205.7
				Norian		~227.3
				Carnian		~237 ^*
			Middle	Ladinian		~241.464 ^*
			Middle	Anisian		246.7
			Lower/Early	Olenekian		249.9
			Lower/Early	Induan		251.902 ± 0.024 ^*
	Paleozoic	Permian	Lopingian	Changhsingian	Pangaea at its maximum extent. Ural and Alleghanian orogenies continue. Hunter-Bowen orogeny, eastern Australia; Sonoma orogeny, western Laurussia. Kazakhstania and Tarim collide with Siberia. Orogenic collapse of Variscan orogeny and early extension along the lines of the future Atlantic, Indian and Southern Oceans. Opening of Neo-Tethys Ocean as Cimmerian terranes rift from northeast Gondwana. Late Paleozoic Ice Age wanes and humid, icehouse climate give way to arid, greenhouse conditions. Global average temperatures rise from c. 12° to over 30° at Permo-Triassic boundary. Desert dune sands and evaporites dominate interior of Pangea. Coal swamps at high latitudes and humid coastal regions. Mosses, Coleoptera (beetles) and Diptera (two-winged flies) appear. Diapsids split into archosaurs (crocodiles and dinosaurs) and lepidosaurs (lizards and snakes). First marine reptiles. Therapsids and cynodonts evolve from synapsids. Guadalupian-Lopingian boundary mass extinction linked to eruption of Emeishan LIP, South China. At the Permo-Triassic boundary, eruption of the Siberian Traps LIP releases vast amounts of CO₂ leading to extreme global warming, and the end-Permian mass extinction. Anoxic waters from the deep ocean move up to the shallows, eliminating trilobites, rugose and tabulate corals, and placoderms. Brachiopods, ammonoids, sharks, bony fish, and crinoids see major reductions. On land, forests disappear. Palaeodictyopterida and many insect groups go extinct, as do all non-therapsid synapsids and most therapsid genera.	254.14 ± 0.07 ^*
			Lopingian	Wuchiapingian		259.51 ± 0.21 ^*
			Guadalupian	Capitanian		264.28 ± 0.16 ^*
				Wordian		266.9 ± 0.4 ^*
				Roadian		274.4 ± 0.4 ^*
			Cisuralian	Kungurian		283.3 ± 0.4
				Artinskian		290.1 ± 0.26 ^*
				Sakmarian		293.52 ± 0.17 ^*
				Asselian		298.9 ± 0.15 ^*
		Carboniferous	Pennsylvanian	Gzhelian	Continuation of the Variscan orogeny (Ouachita and Alleghanian orogenies) with growth of the Central Pangean Mountains. Ural orogeny continues with continental collision between Kazakhstania and Laurussia. Humid, coal swamps form in foreland basins of the Central Pangean Mountains and around North and South China cratons. As the Late Paleozoic icehouse (LPIA) continues, waxing and waning of ice sheets causes rapid changes in global sea level, flooding these regions and depositing cyclothem sequences. Atmospheric oxygen levels rise to over 25% before decreasing again. Appearance of aragonite reef builders, including algae and sponges. Freshwater Eurypterids (sea scorpions). On land, Neoptera appear, and Miomoptera show earliest evidence for complete metamorphosis. First true terrestrial amphibians. Amniotes appear and split into two groups: sauropsids (reptiles) and synapsids (mammals). Lepidodendron and Sigillaria lycopod trees dominate coal swamps, with smaller sphenopsids (horsetails) and seed ferns between. Gymnosperms, including conifers and cycads grow on drier ground. LPIA peaks at Carboniferous-Permian boundary. A drop in CO₂ levels and increase in arid conditions leads to change in woodland vegetation (Carboniferous rainforest collapse).	303.7
Kasimovian				307 ± 0.1
Moscovian				315.2 ± 0.2
Bashkirian				323.4 ^*
Mississippian			Serpukhovian	Continents form a near circle around the opening Paleo-Tethys Ocean. Gondwana forms the southern to southwestern margin; Laurussia the west; Siberia, Amuria and Kazakhstania the north; North and South China the northeast; and, Annamia the eastern margin. The terranes collide with southeastern Laurussia during the Variscan orogeny. Antler orogeny continues, and opening of the Slide Mountain Ocean along western margin of Laurussia. Closure of Ural Ocean between Kazakhstania and Laurussia during the Ural orogeny. Development of Altai accretionary complexes along north and eastern margin of the Paleo-Tethys. Main phase of LPIA begins. Drop in global sea levels, extensive glaciation across Gondwana. Increasing atmospheric oxygen levels. Change from calcite to aragonite seas. Evolutionary radiations after the Late Devonian extinctions include brachiopods, bivalves, echinoderms, ammonoids, gastropods, sharks and ray-finned bony fish. Placoderms and graptolites die out. Proetida only group of trilobites. First freshwater mollusks and sharks. Arthropleura (millipede) largest ever terrestrial arthropod. First flying insects Paleodictyopora. Fish-like (Pederpes) and semi-aquatic tetrapods (Eucritta) appear on land. Seedless vascular plants and seed ferns diversify.	330.3 ± 0.4
			Viséan		346.7 ± 0.4 ^*
			Tournaisian		358.86 ± 0.19 ^*
Devonian		Upper/Late	Famennian	Paleo-Tethys continues to open as the Armorican Terrane Assemblage (ATA) drifts north and Annamia-South China moves away from Gondwana. Rheic Ocean closes as ATA collides with Laurussia beginning the Variscan orogeny. Other orogenies: Antler, Ellesmerian, and Acadian (Laurussia); Achalian (Argentina); Tabberabberan/Lachlan (Australia); Ross (Antarctica); Kazakh (Kazakhstania). Period of high sea-levels, greenhouse conditions but decreasing atmospheric CO₂ levels and slowly cooling climate with glaciations towards end. Vascular plants increase in size, develop large root systems and spread to upland areas. First forests, seed plants, and modern soil orders appear (alfisols and ultisols). Growth of massive reef systems. Major radiation of jawed fish with appearance of ray-finned, lobe-finned, and cartilaginous fish. Appearance of tetrapods (evolved from lobe-finned fish). Early amphibians move on to land. First ammonoids. Emplacement of the Viley and Pripyat–Dniepr–Donets large igneous provinces coincide with global marine anoxic events and the Kellwasser (c. 372 Ma) and Hangenberg (c. 359 Ma) mass extinctions. Kellwasser extinction: c. 20% of families and c. 50% of genera of marine invertebrates lost. Tabulate coral and stromatoporoid reef ecosystems wiped out. Loss of placoderms and many groups of jawless fish. Hangenberg extinction: loss of c. 16% of marine families and c. 21% of marine genera, including ammonoids, ostracods and sharks.	372.15 ± 0.46 ^*
		Upper/Late	Frasnian		382.31 ± 1.36 ^*
		Middle	Givetian		387.95 ± 1.04 ^*
		Middle	Eifelian		393.47 ± 0.99 ^*
		Lower/Early	Emsian		410.62 ± 1.95 ^*
			Pragian		413.02 ± 1.91 ^*
			Lochkovian		419.62 ± 1.36 ^*
Silurian		Pridoli		Laurentia and Avalonia-Baltica collide as Iapetus Ocean closes, Caledonian-Scandian orogeny, and formation of Laurussia. Other orogenies: Salinic (Appalachians); Famatinian (South America) tapers off; Lachlan (Australia). Series of microcontinents and North China separate opening Paleo-Tethys and closing Paleoasian Ocean. Rheic Ocean widens between Gondwana and Laurussia. Siberia drifts north of equator. Temperatures increase as Hirnantian glaciation ends. Sea levels rise. Deposition of black shales, North Africa and Arabia, major hydrocarbon source rocks. Fluctuating climate with glacial advances results in changing ocean conditions causes extinction events, followed by ecological recoveries. Widespread evaporite deposition and hothouse climate by late Silurian. After end-Ordovician mass extinction, major radiation of graptolites, bivalves, gastropods, nautiloids, brachiopods, and crinoids. Increase in trilobites, but never fully recover. Corals and stromatoporiods diversify to produce large reefs. Proliferation of eurypterid arthropods. Earliest jawed fish (acanthodians). Appearance of ostracoderms. Appearance of vascular plants. First land animals including myriapods. First freshwater fish.	422.7 ± 1.6 ^*
		Ludlow	Ludfordian		425 ± 1.5 ^*
		Ludlow	Gorstian		426.7 ± 1.5 ^*
		Wenlock	Homerian		430.6 ± 1.3 ^*
		Wenlock	Sheinwoodian		432.9 ± 1.2 ^*
		Llandovery	Telychian		438.6 ± 1.0 ^*
			Aeronian		440.5 ± 1.0 ^*
			Rhuddanian		443.1 ± 0.9 ^*
Ordovician		Upper/Late	Hirnantian	Most continents lay in equatorial regions. Gondwana stretched to south pole. Panthalassic Ocean covered northern hemisphere. Avalonia rifted from Gondwana closing Iapetus Ocean in front, opening Rheic Ocean behind. South China close to Gondwana; North China between Siberia and Gondwana. Orogenies: Famatinian (South America); Benambran (Australia); Taconic (Laurentia). Baltica and Siberia drift north. Early greenhouse climate, cooling to icehouse conditions during Hirnantian Ice Age. Increase in atmospheric O₂. Great Ordovician Biodiversification Event, major increase in new genera e.g. brachiopods, trilobites, corals, echinoderms, bryozoans, gastropods, bivalves, nautiloids, graptolites, and conodonts. Very high sea levels expand shallow continental seas, increase range of ecological niches. Modern marine ecosystems established. Earliest jawless fish. Tabulate corals and stromatoporoids dominant reef builders. Nautiloids main predators. Appearance of eurypterids and asteroids. Spread of early land plants. Late Ordovician mass extinction, loss of ~85 % of marine invertebrate species. Two pulses: first with onset of glaciation affects tropical fauna; second at end of ice age, warming climate impacts cool water species. Drastic reduction in trilobite, brachiopod, graptolite, echinoderm, conodont, coral, and chitinozoan genera.	445.2 ± 0.9 ^*
			Katian		452.8 ± 0.7 ^*
			Sandbian		458.2 ± 0.7 ^*
		Middle	Darriwilian		469.4 ± 0.9 ^*
		Middle	Dapingian		471.3 ± 1.4 ^*
		Lower/Early	Floian (formerly Arenig)		477.1 ± 1.2 ^*
		Lower/Early	Tremadocian		486.85 ± 1.5 ^*
Cambrian		Furongian	Stage 10	Gondwana stretched from the south pole to equator, separated from Laurentia and Baltica by the Iapetus Ocean. Siberia lay close to the equator, north of Baltica; North and South China close to equatorial Gondwana. Orogenies: Cadomian (N.Africa/southern Europe); Kuunga (central Gondwana); Famatinian orogeny (South America); Delamerian (Australia). Greenhouse climate. High atmospheric CO₂ levels. Atmospheric oxygen levels rose with increase in photosynthesising organisms. Early aragonite seas replaced by mixed aragonite-calcite seas with many animals developing CaCO₃ skeletons. Rapid diversification of animals (Cambrian Explosion), most modern animal phyla appear, e.g. arthropods; molluscs; annelids; echinoderms; bryozoa; priapulids; brachiopods; hemichordates; and, chordates. Radiations of small shelly fossils. Giant anomalocarids (arthropods) dominant predators. Increase in bioturbation and grazing led to decline in stromatolites. Varying oxygen levels in oceans led to series of extinction events followed by radiations, including: earliest Cambrian loss of the Ediacaran acritarchs; end-Botomian extinction, linked to the Kalkarindji large igneous province eruptions (c. 514 Ma) with loss of archaeocyathids (early Cambrian reef builders) and hyoliths; and, end-Cambrian reduction in trilobite diversity. Many fossil lagerstätten, including Burgess Shale and Chengjiang Formation, formed by rapid burial in anoxic conditions.	~491
			Jiangshanian		~494.2 ^*
			Paibian		~497 ^*
		Miaolingian	Guzhangian		~500.5 ^*
			Drumian		~504.5 ^*
			Wuliuan		~506.5
		Series 2	Stage 4		~514.5
		Series 2	Stage 3		~521
		Terreneuvian	Stage 2		~529
		Terreneuvian	Fortunian		538.8 ± 0.6 ^*
Proterozoic	Neoproterozoic	Ediacaran	As Rodinia breaks up Gondwana begins to assemble with the Pan-African (Africa and South America), East African (Africa, India and Arabia) and Kuungan (India, eastern Antarctica and western Australia) orogenies. Rapid rise in eukaryote diversity and numbers, including early animals. First biomineralising animals. First cnidarians (jellyfish and sea pens). 580 Ma Gaskiers glaciation, followed by rise in atmospheric oxygen levels. Ediacaran biota, deep water, soft-bodied organisms. First trace fossils including simple burrows and first evidence of bilateral symmetry.			~635 ^*
		Cryogenian	Rodinia continues to breakup. 720 Ma eruptions of Franklin and Irkutsk LIPs mark rifting of Siberia from Laurentia. Iapetus Ocean begins to open as Amazonia and Baltica drift from Laurentia (from c. 650 Ma). Sturtian (720–658 Ma) and Marinoan (655–635 Ma) Snowball Earth glaciations.			~720
		Tonian	900 Ma Rodinia at its maximum extent. Intracontinental rifting begins c. 850 Ma, associated magmatism becoming widespread from 825 Ma, including the Malani Igneous Suite eruptions, India (c. 775 Ma). Beginning of breakup of Rodinia from c. 750 Ma.			1000
	Mesoproterozoic	Stenian	Collision between Laurentia and Amazonia results in Grenville orogeny which, with Sveconorwegian orogeny in Baltica, mark beginning of assembly of Rodinian supercontinent. Diversification of eukaryotes as oxygen levels increase. All major modern day clades, including Archaeplastida (e.g. red and green algae), Opisthokonta (e.g. fungi) and Amoebozoa appear. Evidence for life on land. Bangiomorpha pubescens (red algae) earliest known sexually reproducing organism.			1200
		Ectasian	Extensive dyke swarms found across all cratons mark completion of breakup of Columbia (Nuna) supercontinent. Oceans have oxygen-rich surface layers and euxinic (no oxygen, high levels of H₂S) deep waters, leading to widespread formation of giant massive sulfide deposits (SEDEX) on the seafloor.			1400
		Calymmian	Columbia continues to fragment with widespread rift-related magmatism. Stromatolites reach their maximum extent and diversity as cyanobacteria diversify and flourish. Primitive seaweeds appear.			1600
	Paleoproterozoic	Statherian	Columbian supercontinent continues to grow along its margins by subduction-related magmatism and terrane accretion. Extension and rift zones begin to develop from c. 1.6 Ga. Eukaryotic red algae appear. Vredefort impact event (2.19 Ga).			1800
		Orosirian	2.0–1.8 Ga Columbia supercontinent assembles during collisional events including Trans-Hudson orogeny (North America), Limpopo Belt (South Africa), Capricorn orogeny (Australia) and Trans-North China orogeny. Drop in atmospheric oxygen as increased volcanism releases carbon dioxide. Grypania represents a possible early eukaryote. Sudbury Impact (1.85 Ga).			2050
		Rhyacian	Massive rise in atmospheric oxygen leads to expansion of life and increased burial of organic matter (Lomagundi carbon isotope excursion) (2.3 to 2.1 Ga). First red beds deposited. Eruptions of Bushveld Magmatic Province (from 2.25 Ga). Orogenies in South America and West Africa mark beginning of Columbia supercontinent. Yarrabubba impact structure (c. 2.23 Ga).			2300
		Siderian	2.5 – 2.42 Ga massive banded iron formations (BIFs) precipitated across most continents. Increasing atmospheric oxygen leads to Great Oxidation Event (c. 2.4––2.3 Ga) and Huronian glaciations as global temperatures drop.			2500
Archean	Neoarchean	Widespread mantle melting and crustal growth followed by formation of supercratons Superia (North America, northwest Europe, South Africa and northwest Australia) and Sclavia (Canada, Zimbabwe, southern India, southwestern Australia, Brazil and North China). Major diversification of cyanobacteria with multicellularity, increasing cell size and specialisation. Proliferation of oxygen-producing life leads to stepwise increase in atmospheric oxygen and deposition of banded iron formation.				2800
	Mesoarchean	Possible onset of plate tectonics c. 3 Ga. Cratons with low relief and extensive shallow marine environments. Weathering increased supply of nutrients to seas. Localised free oxygen associated with carbonate platform stromatolites. Evidence for oxygen-producing photosynthesisers (and possible eukaryotes) c. 3.2 Ga, and terrestrial life c. 3 Ga. Oldest evidence of glaciation c. 2.9 Ga.				3200
	Paleoarchean	Growth of cratons by terrane accretion. Oldest evidence for macroscopic life preserved as stromatolites (c. 3.4 Ga). Evidence for anaerobic prokaryotes in variety of environments including hydrothermal systems and within subsurface sediments. Microbial mats and biofilms become common in shallow water environments.				3600
	Eoarchean	Increasing formation of continental crust. 3.8 – 3.65 Ga chemical traces of life in earliest known sedimentary rocks (Isua Greenstone Belt). Anaerobic prokaryotes including chemotrophs and photosynthesisers appear from c. 3.7 Ga. Early BIFs due to anoxygenic photosynthesis.				4031
Hadean	Earth consolidates from solar nebula over 10-30 million years. Collision with Theia (proto-planet) forms Moon from debris. Core differentiates. Magma ocean cools, releasing CO₂ and water to give CO₂-rich atmosphere. Icy asteroids also contribute water. Mantle convection begins with rapid, shallow plate tectonics or stagnant lid tectonics. Decline in meteorite impacts with last ocean-vaporising impact c. 4.3 Ga. Probable emergence of life after this. Evidence for oldest crust from detrital zircon c. 4.37 Ga. Acasta gneiss complex contains oldest recorded rocks c. 4.03 Ga.					4567.3 ± 0.16

Major proposed revisions to the ICC

Proposed Anthropocene Series/Epoch

Main article: Anthropocene

The Anthropocene is a term for today's time on Earth. It shows how human actions have changed the planet. Scientists first suggested it in 2000. It is not an official part of the geologic time scale yet, but many scientists use it. In 2019, scientists voted to make the Anthropocene an official epoch. They used evidence from Crawford Lake in Ontario. But in early 2024, it was not accepted as an official epoch. It is still a helpful way to talk about how humans affect Earth.

Proposals for revisions to pre-Cryogenian timeline

Shields et al. 2021

Scientists suggested changes to how we split very old Earth time, from before the Cryogenian period. They made these ideas in 2021, but they were not accepted. There were concerns from other scientists. The suggestions included splitting the Archean Eon into three parts instead of four and other changes to match rock records better.

Van Kranendonk et al. 2012 (GTS2012)

In 2012, a book suggested big changes to how we understand the oldest parts of Earth's history. These changes would focus on important events like the formation of the Solar System and the Great Oxidation Event. But as of 2022, these changes were not accepted by the group that sets these rules. The ideas included new names for eras and periods, like Chaotian and Jack Hillsian for the Hadean, and many new divisions in the Archean and Proterozoic.

Extraterrestrial geologic time scales

Main articles: Lunar geologic timescale, Martian geologic timescale, and Geology of Venus

Other planets and satellites in the Solar System, like Venus, Mars, and Earth's Moon, have features that help us learn about their past. But big planets with lots of gas cannot keep records of their history the same way. Making one time scale for all planets does not help much when we study Earth, except when we look at the whole Solar System.

The geologic history of Earth's Moon has different periods. These periods are based on things like impact cratering, volcanism, and erosion. The periods are called Pre-Nectarian, Nectarian, Imbrian, Eratosthenian, and Copernican. The Moon is special because people have collected rock samples from there.

The geological history of Mars can be studied in two ways. One way counts impact craters to split Mars into four periods: Pre-Noachian, Noachian, Hesperian, and Amazonian. The other way uses minerals seen from space to split Mars into three periods: Phyllocian, Theiikian, and Siderikian.