4.57 billion years ago – 2026·102 events
Geologic Time Scale: Earth's 4.6-Billion-Year History
All 102 events
In date order. Indented events happen within the event above them. Last updated September 24, 2026.
4.57 billion years ago – 538.8 million years ago · Geologic time
Precambrian
The informal name for everything before the Cambrian: the Hadean, Archean and Proterozoic eons. It covers about 4 billion years, 88% of Earth's history, from the planet's formation to the spread of animals with shells.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Precambrian
4.57 billion years ago – 4.03 billion years ago · Geologic time
Hadean Eon
Earth's first eon, about 536 million years, named for Hades, the Greek god of the underworld. The chart starts it at 4,567 million years ago, the age of the oldest solids in the solar system. Almost no rock survives from it.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Hadean
4.03 billion years ago – 2.5 billion years ago · Geologic time
Archean Eon
About 1.53 billion years, named from the Greek arkhe, 'beginning'. Earth had continental crust and oceans but almost no free oxygen, and the first fossil evidence of life appears. Its start is the age of the oldest known intact rocks.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Archean; Wikipedia, Hadean
4.03 billion years ago – 3.6 billion years ago · Geologic time
Eoarchean Era
The first era of the Archean, 431 million years long. Some estimates place the beginning of life in it. The atmosphere had no free oxygen.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Eoarchean
3.6 billion years ago – 3.2 billion years ago · Geologic time
Paleoarchean Era
A 400-million-year era holding the earliest confirmed evidence of life. Like most Precambrian units, it is defined by fixed ages rather than by a marker in a rock section.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Paleoarchean
3.2 billion years ago – 2.8 billion years ago · Geologic time
Mesoarchean Era
A 400-million-year era that contains the first evidence of modern-style plate subduction and an expansion of microbial life.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Mesoarchean
2.8 billion years ago – 2.5 billion years ago · Geologic time
Neoarchean Era
The last Archean era, 300 million years long, marked by the growth of continents.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Neoarchean
2.5 billion years ago – 538.8 million years ago · Geologic time
Proterozoic Eon
The longest eon, nearly 2 billion years. Its name means 'earlier life' in Greek. It runs from the first rise of free oxygen in the air to just before the Cambrian, and includes the first multicellular life and the Snowball Earth glaciations.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Proterozoic
2.5 billion years ago – 1.6 billion years ago · Geologic time
Paleoproterozoic Era
The longest era in Earth's history, 900 million years. The Great Oxidation Event falls in it. Fossil evidence suggests that about 1.8 billion years ago a day lasted about 20 hours, making a year of about 450 days.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Paleoproterozoic
2.5 billion years ago – 2.3 billion years ago · Geologic time
Siderian Period
Named from the Greek sideros, 'iron', for the banded iron formations laid down in it. 200 million years long.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Siderian
2.3 billion years ago – 2.05 billion years ago · Geologic time
Rhyacian Period
Named from the Greek rhyas, 'stream of lava', for large layered igneous intrusions in South Africa. 250 million years long.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Rhyacian
2.05 billion years ago – 1.8 billion years ago · Geologic time
Orosirian Period
Named from the Greek oroseira, 'mountain range'. 250 million years long.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Orosirian
1.8 billion years ago – 1.6 billion years ago · Geologic time
Statherian Period
Named from the Greek statheros, 'stable'. Oxygen in the air was 10% to 20% of today's level. 200 million years long.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Statherian
1.6 billion years ago – 1 billion years ago · Geologic time
Mesoproterozoic Era
A 600-million-year era, the first with a fairly complete surviving rock record. Its continents were roughly today's landmasses in a different arrangement, and the supercontinent Rodinia assembled during it.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Mesoproterozoic; Wikipedia, Rodinia
1.6 billion years ago – 1.4 billion years ago · Geologic time
Calymmian Period
Named from the Greek kalymma, 'cover', for the spread of sediment platforms over the continents. 200 million years long.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Calymmian
1.4 billion years ago – 1.2 billion years ago · Geologic time
Ectasian Period
Named from the Greek ektasis, 'extension'. Estimates put the length of a day at its start at about 17 and a half hours. 200 million years long.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Ectasian
1.2 billion years ago – 1 billion years ago · Geologic time
Stenian Period
Named from the Greek stenos, 'narrow'. The supercontinent Rodinia finished assembling in this period. 200 million years long.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Stenian
1 billion years ago – 538.8 million years ago · Geologic time
Neoproterozoic Era
The last era of the Precambrian, about 461 million years. It includes the Snowball Earth glaciations and the first fossils of complex multicellular life.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Neoproterozoic
1000 million years ago – c. 720 million years ago · Geologic time
Tonian Period
Named from the Greek tonos, 'stretch', for the rifting that began to break up Rodinia. About 280 million years long; the chart gives its end as approximate.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Tonian
c. 720 million years ago – c. 635 million years ago · Geologic time
Cryogenian Period
Greek for 'cold birth'. About 85 million years dominated by two global glaciations, the Sturtian and the Marinoan. Both of its boundaries are still approximate on the chart.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Cryogenian
c. 635 million years ago – 538.8 million years ago · Geologic time
Ediacaran Period
Named for the Ediacara Hills of South Australia. Ratified in 2004, it was the first new geologic period declared in 120 years. Its rocks hold the oldest known complex multicellular organisms.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Ediacaran
4.54 billion years ago · Earth and climate
Earth forms
Earth grew from the disk of gas and dust around the young Sun. The USGS gives its age as 4.54 billion years, with less than 1% uncertainty, from lead isotope dating of meteorites and ancient lead ores.
c. 4.5 billion years ago · Earth and climate
A giant impact forms the Moon
The leading explanation: a Mars-sized body, called Theia, struck the young Earth, and debris from the collision gathered into the Moon. Apollo rock samples suggest this happened about 60 million years after the solar system began to form.
Sources: NASA, How the Moon Formed; Wikipedia, Giant-impact hypothesis
4.4 billion years ago · Earth and climate
Oldest known mineral grain crystallizes
A zircon crystal from the Jack Hills of Western Australia, dated to 4,404 million years, is the oldest known material formed on Earth. Oxygen isotopes in these zircons point to liquid water at the surface in the Hadean.
Sources: Wikipedia, Jack Hills; USGS, Age of the Earth
c. 4.02 billion years ago · Earth and climate
Oldest known intact rocks form
The Acasta Gneiss in Canada's Northwest Territories holds fragments of the oldest known crust. Its oldest unit has zircons dated to 4.02 billion years; the USGS gives 4.03 billion.
c. 3.48 billion years ago · Life
Earliest widely accepted fossils
Stromatolites, layered mounds built by microbial mats, in the Dresser Formation of Western Australia are the oldest direct fossil evidence of life. Older traces are claimed: graphite in 3.7-billion-year-old Greenland rocks and in a 4.1-billion-year-old zircon.
Sources: Wikipedia, Earliest known life forms; Wikipedia, Paleoarchean
c. 2.46 billion years ago – c. 2.06 billion years ago · Earth and climate
Great Oxidation Event
Oxygen made by photosynthesizing cyanobacteria built up in the air and shallow seas for the first time. Over about 400 million years it rose to perhaps 10% of today's level, which was toxic to many microbes that had evolved without it.
Sources: Wikipedia, Great Oxidation Event; Wikipedia, Siderian
1.05 billion years ago · Life
First known sexually reproducing organism
Bangiomorpha pubescens, a multicellular red alga from Somerset Island in Arctic Canada, dated to 1,047 million years ago. It closely resembles the living red alga Bangia. Earlier estimates put these fossils at about 1.2 billion years.
Sources: Wikipedia, Bangiomorpha; Wikipedia, Eukaryote
c. 717 million years ago – c. 635 million years ago · Earth and climate
Snowball Earth glaciations
In the Cryogenian, ice sheets may have reached the equator during two long glaciations. Scientists still debate whether the oceans froze almost completely or kept a band of open water near the equator.
Sources: Wikipedia, Snowball Earth; Wikipedia, Cryogenian
c. 717 million years ago – c. 660 million years ago · Earth and climate
Sturtian glaciation
The first and longer Cryogenian glaciation, lasting about 57 million years.
c. 650 million years ago – c. 635 million years ago · Earth and climate
Marinoan glaciation
The second Cryogenian glaciation, about 15 million years long. It ended about 635 million years ago, where the chart places the start of the Ediacaran.
Sources: Wikipedia, Snowball Earth; International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06
c. 575 million years ago · Life
Ediacaran organisms spread
Large, soft-bodied organisms shaped like fronds, tubes and discs spread after the Cryogenian glaciations. They are the earliest known complex multicellular organisms, and most disappeared as the Cambrian explosion began.
Sources: Wikipedia, Ediacaran biota; UC Berkeley Museum of Paleontology, The Cambrian Period
538.8 million years ago – 2026 · Geologic time
Phanerozoic Eon
The current eon, about 539 million years so far. Its name means 'visible life': it begins with the Cambrian, when animals with hard shells became common fossils. It holds the Paleozoic, Mesozoic and Cenozoic eras.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Phanerozoic
538.8 million years ago – 251.9 million years ago · Geologic time
Paleozoic Era
Named from the Greek for 'ancient life'. Its six periods span about 287 million years, from the Cambrian explosion to the end-Permian extinction, the largest in the fossil record.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Paleozoic; UC Berkeley Museum of Paleontology, The Paleozoic Era
538.8 million years ago – 486.85 million years ago · Geologic time
Cambrian Period
About 52 million years, named for Cambria, the Latin name for Wales, where Adam Sedgwick studied its rocks in 1831. Almost every animal phylum with hard parts first appears in its rocks.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Cambrian; UC Berkeley Museum of Paleontology, The Cambrian Period
486.85 million years ago – 443.1 million years ago · Geologic time
Ordovician Period
About 44 million years, named for the Ordovices, a Welsh tribe. Seas held diverse trilobites, brachiopods and graptolites, and spores show plants reaching land. It ended with glaciation and mass extinction.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Ordovician; UC Berkeley Museum of Paleontology, The Ordovician Period
443.1 million years ago – 419.62 million years ago · Geologic time
Silurian Period
The shortest Paleozoic period, about 23.5 million years, named for the Silures, a tribe of Wales. The oldest known coral reefs, the first jawed fish and the earliest vascular plant fossils date from it.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Silurian; UC Berkeley Museum of Paleontology, The Silurian Period
419.62 million years ago – 358.86 million years ago · Geologic time
Devonian Period
About 61 million years, named for Devon in England. Plants spread across the land and formed the first forests, and the first four-limbed vertebrates and land arthropods appeared.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Devonian; UC Berkeley Museum of Paleontology, The Devonian Period
358.86 million years ago – 298.9 million years ago · Geologic time
Carboniferous Period
About 60 million years. The name means 'coal-bearing': swamp forests laid down coal beds worldwide. Oxygen rose to an estimated 25% to 30% of the air. In North America it is split into the Mississippian and Pennsylvanian.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Carboniferous; UC Berkeley Museum of Paleontology, The Carboniferous Period
298.9 million years ago – 251.9 million years ago · Geologic time
Permian Period
About 47 million years, named for the Perm region of Russia. The land was joined in Pangaea, and reptiles and synapsids, the mammals' ancestors, spread through its dry interior. It ended in the largest mass extinction.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Permian; UC Berkeley Museum of Paleontology, The Permian Period
251.9 million years ago – 66 million years ago · Geologic time
Mesozoic Era
'Middle life', often called the Age of Dinosaurs. About 186 million years bounded by two mass extinctions, with a mostly hot climate and the breakup of the supercontinent Pangaea.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Mesozoic; UC Berkeley Museum of Paleontology, The Mesozoic Era
251.9 million years ago – 201.4 million years ago · Geologic time
Triassic Period
About 50.5 million years, named for a set of three rock layers in southern Germany. Survivors of the end-Permian extinction spread out, and the first dinosaurs appeared late in the period. It also ended in mass extinction.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Triassic; UC Berkeley Museum of Paleontology, The Triassic Period
201.4 million years ago – 143.1 million years ago · Geologic time
Jurassic Period
About 58 million years, named for the Jura Mountains. Giant sauropods, pterosaurs and the first birds lived as Pangaea split apart. Its end is the only period boundary still without a formal definition.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Jurassic; UC Berkeley Museum of Paleontology, The Jurassic Period
143.1 million years ago – 66 million years ago · Geologic time
Cretaceous Period
The longest Phanerozoic period, about 77 million years, named from the Latin creta, 'chalk'. Seas were high and warm, flowering plants appeared, and it ended with the Chicxulub impact.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Cretaceous; UC Berkeley Museum of Paleontology, The Cretaceous Period
66 million years ago – 2026 · Geologic time
Cenozoic Era
'New life', often called the Age of Mammals. The last 66 million years, from the Chicxulub impact to today, as mammals and birds diversified and the continents moved into their present positions.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Cenozoic; UC Berkeley Museum of Paleontology, The Cenozoic Era
66 million years ago – 23.04 million years ago · Geologic time
Paleogene Period
About 43 million years. Survivors of the end-Cretaceous extinction, above all mammals and birds, filled the empty niches. With the Neogene it covers the time once called the Tertiary.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Paleogene
66 million years ago – 56 million years ago · Geologic time
Paleocene Epoch
About 10 million years, bracketed by the Chicxulub impact at its start and a sudden global warming, the Paleocene-Eocene Thermal Maximum, at its end.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Paleocene
56 million years ago – 33.9 million years ago · Geologic time
Eocene Epoch
About 22 million years; the name means 'dawn of the new'. Earth's average temperature at its start was about 27 °C. It ended with cooling and extinctions at the Eocene-Oligocene transition.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Eocene
33.9 million years ago – 23.04 million years ago · Geologic time
Oligocene Epoch
About 11 million years, from Greek words for 'few new'. Grasslands expanded and tropical broadleaf forests retreated.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Oligocene
23.04 million years ago – 2.58 million years ago · Geologic time
Neogene Period
About 20.5 million years. The climate cooled toward the ice ages, the Isthmus of Panama joined North and South America late in the period, and the first humans appeared in Africa near its end.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Neogene
23.04 million years ago – 5.33 million years ago · Geologic time
Miocene Epoch
About 17.7 million years, named by Charles Lyell. Late in the epoch the Mediterranean was cut off from the Atlantic and nearly dried up, an episode called the Messinian salinity crisis.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Miocene
5.33 million years ago – 2.58 million years ago · Geologic time
Pliocene Epoch
About 2.75 million years. Before a 2009 revision it also included the Gelasian stage, so older sources end it about 1.8 million years ago.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Pliocene
2.58 million years ago – 2026 · Geologic time
Quaternary Period
The current period, the last 2.58 million years, defined by cycles of glaciation that are still going on. It holds the Pleistocene and Holocene epochs.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Quaternary
2.58 million years ago – 11.7 thousand years ago · Geologic time
Pleistocene Epoch
The Ice Age epoch, about 2.57 million years of repeated glaciations. At peak glaciation, sea level fell by as much as 120 m. Its end matches the end of the last glacial period.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Pleistocene
11.7 thousand years ago – 2026 · Geologic time
Holocene Epoch
The current epoch: the 11,700 years since the last glacial period ended. It is a warm interlude within the Quaternary glacial cycles and holds all of recorded history.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Holocene
11.7 thousand years ago – 6,201 BC · Geologic time
Greenlandian Age
The first age of the Holocene, ratified in 2018. Its start is marked in the NorthGRIP ice core from central Greenland, at the end of the Younger Dryas cold spell.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Greenlandian
6,201 BC – 2,201 BC · Geologic time
Northgrippian Age
Named for the North Greenland Ice Core Project. It begins near the 8.2-kiloyear event, a drop in global temperatures that lasted two to four centuries.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Northgrippian; Wikipedia, 8.2-kiloyear event
2,201 BC – 2026 · Geologic time
Meghalayan Age
The current age, named for Meghalaya in northeast India, where a cave stalagmite marks its start. It began with the 4.2-kiloyear event, a drought that lasted about 200 years.
Sources: International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06; Wikipedia, Meghalayan; Wikipedia, 4.2-kiloyear event
· Geologic time
Geologists reject an Anthropocene epoch
After about 15 years of study, the ICS Subcommission on Quaternary Stratigraphy voted 12 to 4 against an Anthropocene epoch beginning in 1950, and the IUGS upheld the vote. The ICS says the term will stay in informal use.
Sources: International Commission on Stratigraphy, Joint statement by the IUGS and ICS on the Anthropocene; Wikipedia, Anthropocene
c. 538.8 million years ago · Life
Cambrian explosion
Almost every animal phylum with hard parts appears in the fossil record over about 13 to 25 million years. Animals began actively hunting, burrowing deeply and building shells, which fossilize far better than soft bodies.
Sources: Wikipedia, Cambrian explosion; UC Berkeley Museum of Paleontology, The Cambrian Period
c. 505 million years ago · Life
Burgess Shale animals
This fossil bed in the Canadian Rockies, found by Charles Walcott on August 30, 1909, preserves the soft parts of Cambrian animals. Walcott spent the rest of his life, until 1927, describing its fossils.
Sources: Wikipedia, Burgess Shale
c. 470 million years ago · Life
First plants on land
Spores called cryptospores in Middle Ordovician rocks from Saudi Arabia and other parts of Gondwana are the earliest evidence of land plants. Land plants descend from freshwater green algae.
Sources: Wikipedia, Evolution of plants; Wikipedia, Embryophyte; UC Berkeley Museum of Paleontology, The Ordovician Period
c. 444 million years ago · Mass extinctions
End-Ordovician mass extinction
Two pulses, tied to a southern glaciation and the thaw that followed. About 85% to 86% of species died out, making it the second-largest of the Big Five by share of genera lost.
Sources: National Park Service, Mass Extinctions Through Geologic Time; Our World in Data, There have been five mass extinctions in Earth's history; Wikipedia, Extinction event
c. 433 million years ago · Life
Cooksonia, an early vascular plant
A small, leafless plant with the oldest known stem containing vascular tissue for carrying water. Its fossils span about 433 to 393 million years ago and were first found in Britain in 1937.
Sources: Wikipedia, Cooksonia
c. 385 million years ago · Life
Earliest known trees
Fossils from Gilboa, New York, show Wattieza, a fern-like tree at least 8 m tall that reproduced with spores. By the end of the Devonian, ferns, horsetails and seed plants formed the first forests.
Sources: Wikipedia, Wattieza; UC Berkeley Museum of Paleontology, The Devonian Period
c. 375 million years ago · Life
Tiktaalik, a fish with limb-like fins
Found in 2004 on Ellesmere Island in Arctic Canada, this lobe-finned fish had scales and gills but also sturdy fin bones that could prop up its body. It is a transitional form between fish and four-legged animals.
Sources: Wikipedia, Tiktaalik; UC Berkeley Museum of Paleontology, The Devonian Period
c. 372 million years ago – c. 359 million years ago · Mass extinctions
Late Devonian extinctions
A series of crises over about 13 million years. About 75% of species were lost across the interval, by the NPS estimate. Accounts differ on severity: one estimate puts the main Kellwasser pulse at about 40% of marine species.
Sources: National Park Service, Mass Extinctions Through Geologic Time; Our World in Data, There have been five mass extinctions in Earth's history; Wikipedia, Kellwasser event
c. 372 million years ago · Mass extinctions
Kellwasser event
The main Late Devonian extinction, at the boundary between the Frasnian and Famennian ages, about 372 million years ago.
Sources: Wikipedia, Kellwasser event
c. 359 million years ago · Mass extinctions
Hangenberg event
A second extinction about 13 million years after Kellwasser that closed the Devonian. It is named after a shale in Germany's Rhenish Massif.
Sources: Wikipedia, Hangenberg event
c. 335 million years ago · Earth and climate
Pangaea assembles
Gondwana, Euramerica and Siberia merged into the supercontinent Pangaea during the Carboniferous. It was C-shaped, stretched between the poles, and was surrounded by the superocean Panthalassa.
Sources: Wikipedia, Pangaea; UC Berkeley Museum of Paleontology, The Permian Period
318 million years ago · Life
Hylonomus, an early reptile-like animal
Long described as the earliest known reptile, this small animal lived about 318 million years ago in what is now Nova Scotia. A 2025 analysis placed it just outside the group that includes all living reptiles and mammals.
Sources: Wikipedia, Hylonomus
c. 300 million years ago · Life
Meganeura, a giant flying insect
A dragonfly-like insect with a wingspan of about 65 to 75 cm, first found in the coal beds of Commentry, France, in 1880. Carboniferous air held more oxygen than today's.
Sources: Wikipedia, Meganeura; Wikipedia, Carboniferous
c. 252 million years ago · Earth and climate
Siberian Traps erupt
Lava flooded a large part of Siberia in one of the largest volcanic events of the last 500 million years. Eruptions lasted roughly 2 million years across the Permian-Triassic boundary and are thought to be the main cause of the end-Permian extinction.
Sources: Wikipedia, Siberian Traps; Wikipedia, Permian–Triassic extinction event
251.9 million years ago · Mass extinctions
End-Permian extinction, the Great Dying
The largest known mass extinction. Estimates range from about 81% of marine species to 96% of all species. Trilobites vanished, and recovery did not begin until four to six million years later.
Sources: National Park Service, Mass Extinctions Through Geologic Time; Wikipedia, Permian–Triassic extinction event; Wikipedia, Extinction event
c. 233 million years ago · Life
Earliest well-dated dinosaurs
The oldest securely dated dinosaur fossils come from Brazil's Santa Maria Formation, about 233 million years old, and Argentina's Ischigualasto Formation, home of Eoraptor. Nyasasaurus from Tanzania may push their origin back to about 243 million years.
Sources: Wikipedia, Dinosaur; Wikipedia, Eoraptor
c. 205 million years ago · Life
Early mammal relative Morganucodon
Morganucodon, a small mammaliaform first found in Glamorgan, Wales, appeared about 205 million years ago. Its fossils are also known from China, elsewhere in Europe and North America.
Sources: Wikipedia, Morganucodon
201.4 million years ago · Mass extinctions
End-Triassic extinction
About 80% of species were lost, by the NPS estimate, including most therapsids and nearly all large amphibians, which left dinosaurs with little competition on land. It coincides with the Central Atlantic eruptions.
Sources: National Park Service, Mass Extinctions Through Geologic Time; Wikipedia, Extinction event; Wikipedia, Triassic–Jurassic extinction event
c. 201 million years ago · Earth and climate
Central Atlantic volcanic eruptions
Basalt eruptions covering about 11 million km², the largest continental igneous province known, formed as Pangaea began to split. They are linked to the end-Triassic extinction.
Sources: Wikipedia, Central Atlantic magmatic province; Wikipedia, Jurassic
c. 200 million years ago · Earth and climate
Pangaea begins to break apart
Rifting split Pangaea into Laurasia in the north and Gondwana in the south, and later opened the Atlantic. Accounts differ on timing: the USGS gives 225 to 200 million years ago; other sources range from the Middle Triassic to about 175 million years ago.
Sources: USGS, This Dynamic Earth: Historical perspective; Wikipedia, Pangaea; UC Berkeley Museum of Paleontology, The Triassic Period
c. 150 million years ago · Life
Archaeopteryx
A feathered, bird-like dinosaur about the size of a magpie from what is now southern Germany. For over a century it was accepted as the oldest known bird; older candidates have since been found.
Sources: Wikipedia, Archaeopteryx; UC Berkeley Museum of Paleontology, The Jurassic Period
c. 130 million years ago · Life
Earliest known flowering plant fossil
Montsechia vidalii, an aquatic plant from Spain about 130 million years old, is the earliest known flowering plant macrofossil. Flowering plants spread through the Cretaceous.
Sources: Wikipedia, Montsechia; UC Berkeley Museum of Paleontology, The Cretaceous Period
c. 100 million years ago · Life
Titanosaurs reach record size
Argentinosaurus, from Neuquén Province, Argentina, is estimated at 30 to 35 m long and 65 to 80 tonnes, among the largest land animals ever. Accounts of its age differ: its rock unit has been placed both before and after 100 million years ago.
c. 68 million years ago · Life
Tyrannosaurus rex
One of the last non-avian dinosaurs. Its fossils come from rocks of the late Maastrichtian age, 69 to 66 million years ago.
Sources: Wikipedia, Tyrannosaurus
66 million years ago · Earth and climate
Asteroid strikes Chicxulub
An asteroid about 10 km wide hit what is now the Yucatán Peninsula of Mexico. Its crater, about 200 km across, lies buried under about 1 km of younger rock. The impact is tied to the end-Cretaceous mass extinction.
Sources: Wikipedia, Chicxulub crater; Wikipedia, Cretaceous–Paleogene extinction event
66 million years ago · Mass extinctions
End-Cretaceous extinction
About 76% of species disappeared, including all non-avian dinosaurs, plesiosaurs, mosasaurs and ammonites. Mammals and birds became the main land vertebrates afterward.
Sources: National Park Service, Mass Extinctions Through Geologic Time; Our World in Data, There have been five mass extinctions in Earth's history; Wikipedia, Extinction event
56 million years ago · Earth and climate
Paleocene-Eocene Thermal Maximum
A huge release of carbon into the ocean and air raised global average temperature by 5 to 8 °C. The warm spike lasted about 200,000 years and marks the start of the Eocene.
Sources: Wikipedia, Paleocene–Eocene Thermal Maximum; Wikipedia, Paleocene
c. 34 million years ago · Earth and climate
Antarctic ice sheet expands
Ice began to build on Antarctica between 60 and 45.5 million years ago and spread at the Eocene-Oligocene transition. Today the sheet averages over 2 km thick and holds about 61% of Earth's fresh water.
Sources: Wikipedia, Antarctic ice sheet
c. 7 million years ago · Humans
Sahelanthropus, among the earliest hominins
A skull nicknamed Toumai, found in northern Chad in 2001, is dated to between 7 and 6 million years ago. It showed that early human relatives lived beyond East Africa's Rift Valley and South Africa.
Sources: Smithsonian Human Origins, Sahelanthropus tchadensis; Wikipedia, Sahelanthropus
c. 3.3 million years ago · Humans
Oldest known stone tools
Artifacts at Lomekwi, on the west bank of Lake Turkana in Kenya, date to 3.3 million years ago, older than any known fossil of the genus Homo. The Oldowan toolkit appears by 2.6 million years ago.
Sources: Wikipedia, Lomekwi; Smithsonian Human Origins, Early Stone Age Tools
c. 3.2 million years ago · Humans
Lucy
A skeleton about 40% complete of Australopithecus afarensis, found at Hadar, Ethiopia, in 1974. Her species walked upright but had a brain under 500 cubic centimeters, and lived from about 3.85 to 2.95 million years ago.
Sources: Wikipedia, Lucy (Australopithecus); Smithsonian Human Origins, Australopithecus afarensis
c. 2.8 million years ago – 2026 · Humans
Genus Homo
The oldest fossil assigned to Homo is a jaw fragment from the Afar region of Ethiopia, dated to 2.8 million years ago. Homo habilis lived from about 2.4 to 1.4 million years ago. Homo sapiens is the only living species.
Sources: Wikipedia, Homo; Smithsonian Human Origins, Homo habilis
c. 1.89 million years ago · Humans
Homo erectus
Lived from about 1.89 million to 110,000 years ago, with human-like body proportions. Generally considered the first human species to spread beyond Africa, it is linked to the earliest hand axes and hearths.
c. 300 thousand years ago – 2026 · Humans
Homo sapiens evolves in Africa
Our species evolved in Africa during a period of major climate change. Fossils from Jebel Irhoud, Morocco, dated to about 315,000 years ago are the oldest known. 300,000 years is less than 0.01% of Earth's age.
Sources: Smithsonian Human Origins, Homo sapiens; Wikipedia, Jebel Irhoud
c. 12 thousand years ago · Humans
Farming begins
After the last ice age, plants and animals were domesticated in several regions. In the Fertile Crescent it began between about 10,000 and 8,000 BCE, with einkorn and emmer wheat, barley, lentils and peas among the first crops.
Sources: Wikipedia, Neolithic Revolution
c. 3,300 BC · Humans
Writing appears in Mesopotamia
The first undoubted written documents, proto-cuneiform tablets from Uruk in southern Mesopotamia, date from about 3300 BC. Most record accounts. All of recorded history fits within the last 5,300 years.
Sources: Wikipedia, Cuneiform
c. 2,600 BC · Humans
Great Pyramid of Giza built
Built as the tomb of the pharaoh Khufu around 2600 BC, over about 26 years. The Meghalayan, the current age of geologic time, began about four centuries later.
Sources: Wikipedia, Great Pyramid of Giza; International Commission on Stratigraphy, International Chronostratigraphic Chart v2026/06
1815 · Humans
William Smith's geological map
William Smith published the first detailed geological map of a whole country, 'A Delineation of the Strata of England and Wales, with part of Scotland'. He was later called the father of English geology.
Sources: Wikipedia, William Smith (geologist)
1956 · Humans
Earth dated to 4.55 billion years
Clair Patterson of Caltech used lead isotopes from the Canyon Diablo meteorite to calculate an age for Earth of 4.55 billion years. His figure has remained largely unchallenged since.
Sources: Wikipedia, Clair Cameron Patterson; USGS, Age of the Earth
· Humans
Apollo 11 lands on the Moon
Neil Armstrong and Buzz Aldrin collected 21.5 kg of lunar rock and soil. Apollo samples later helped date the Moon's formation to about 60 million years after the solar system began.
c. 40 thousand years ago · Humans
Neanderthals disappear
Our closest extinct relatives lived from about 400,000 years ago. They vanished within a few thousand years of modern humans moving into Europe.
2.58 million years ago · Earth and climate
Quaternary ice age cycles begin
Ice sheets began growing and shrinking in repeated glacial and interglacial cycles linked to changes in Earth's orbit. The cycles continue; Earth is now in an interglacial.
Sources: Wikipedia, Quaternary glaciation; Wikipedia, Quaternary
c. 26 thousand years ago – c. 20 thousand years ago · Earth and climate
Last Glacial Maximum
Ice sheets reached their greatest recent extent, covering much of northern North America, northern Europe and Asia. Sea levels dropped and deserts expanded.
Sources: Wikipedia, Last Glacial Maximum; Wikipedia, Pleistocene