The History of Earth
posted: 26-Sep-2026 & updated: 26-Sep-2026
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From the Big Bang to the invention of writing — 13.8 billion years in one sweep. Where this page ends (c. 3000 BC, the Bronze Age and writing), the World History notes begin.
- The Cosmos — from the Big Bang to the Solar System
- The Geologic Time Scale — the big picture
- The Precambrian — birth of Earth and of life
- The Paleozoic — the explosion of life and the move onto land
- The Mesozoic — the age of dinosaurs
- The Cenozoic — mammals and apes
- The Five Mass Extinctions
- When coal, oil and natural gas were made
- Human Evolution — from Australopithecus to Homo sapiens
- Homo sapiens — from the Cognitive Revolution to civilization
Dates are given as years ago. Geologists write Ga (billion years), Ma (million years) and ka (thousand years) — e.g. 2.5 Ga = 2.5 billion years ago, 66 Ma = 66 million years ago, 70 ka = 70,000 years ago.
The Cosmos — from the Big Bang to the Solar System
| When | Event | What happened |
|---|---|---|
| 13.8 billion years ago | The Big Bang | The beginning of space, time, matter and energy. In the first 10⁻³² s, inflation smooths the universe; within 3 minutes, hydrogen and helium nuclei form |
| 13.8 billion years ago + 380,000 years | Cosmic background radiation | The universe cools enough for atoms to form and light travels freely — the cosmic microwave background (CMB) we observe today is this light. Then come the “dark ages”, before any stars. |
| c. 13.7 billion years ago | The first stars | 100–200 million years after the Big Bang. Giant stars of pure hydrogen and helium — inside them, fusion forges the first heavy elements (carbon, oxygen, iron…), which supernovae scatter into space |
| c. 13.6 billion years ago | Our galaxy | The oldest stars of the Milky Way were born around this time. Small galaxies merged and grew into a disk about 100,000 light-years across. |
| 4.6 billion years ago | The Sun and Solar System | A molecular cloud on the galaxy’s outskirts collapses (nudged by a nearby supernova) → the Sun ignites. Planets clump together from the leftover disk. We live around a second- or third-generation star, made of elements that earlier supernovae spread. |
| 4.54 billion years ago | Earth | Formed by collisions and mergers of planetesimals. At first a magma ocean |
| 4.5 billion years ago | The Moon | A Mars-sized body, Theia, strikes Earth (giant-impact hypothesis) → the debris coalesces into the Moon. The Moon stabilizes Earth’s axial tilt and thus its climate |
| 4.4–4.0 billion years ago | Oceans | The crust solidifies (zircon crystals 4.4 billion years old) and water vapour condenses into oceans. Asteroids and comets may have added water |
| 4.1–3.8 billion years ago | Late Heavy Bombardment | Migrating orbits of Jupiter and Saturn send asteroids raining down — most of the Moon’s large craters date from this time. |
- Of the universe’s 13.8 billion years, Earth accounts for 4.5 billion — it appeared in the last third of cosmic history.
- Of the elements in your body, only the hydrogen comes from the Big Bang; all the rest (carbon, oxygen, calcium, iron…) were made inside earlier generations of stars and in supernovae. “We are made of star stuff” (Carl Sagan).
The Geologic Time Scale — the big picture
Earth’s 4.54 billion years are divided into eons → eras → periods → epochs. The boundaries mostly mark mass extinctions or abrupt turnovers in life.
| Eon | Era | Periods | Span | One-line summary |
|---|---|---|---|---|
| Hadean | — | — | 4.54–4.0 billion years ago | Magma ocean, formation of the Moon and the oceans. Almost no rock record |
| Archean | — | — | 4.0–2.5 billion years ago | The first life (prokaryotes), stromatolites, the beginning of photosynthesis |
| Proterozoic | — | — | 2.5 billion–539 million years ago | Great Oxidation Event, eukaryotes, multicellular life, Snowball Earth, Ediacaran biota |
| Phanerozoic | Paleozoic | Cambrian · Ordovician · Silurian · Devonian · Carboniferous · Permian | 539–252 million years ago | Cambrian explosion → fish → land plants and amphibians → coal forests → reptiles. Ends with the end-Permian extinction |
| Phanerozoic | Mesozoic | Triassic · Jurassic · Cretaceous | 252–66 million years ago | The age of dinosaurs. Mammals, birds and flowering plants appear. Ends with an asteroid impact |
| Phanerozoic | Cenozoic | Paleogene · Neogene · Quaternary | 66 million years ago–present | The age of mammals. Primates → apes → humans. Ice ages |
- The Precambrian (Hadean, Archean, Proterozoic) is 88% of Earth’s history; the history of visible life (the Phanerozoic) is only the last 12%.
- Each era ends with a mass extinction: end of the Paleozoic (end-Permian) = the largest ever; end of the Mesozoic (end-Cretaceous) = the dinosaurs. See the Five Mass Extinctions.
The Precambrian — birth of Earth and of life
| When | Event | What happened |
|---|---|---|
| 4.0 billion years ago | Archean begins | The first continental crust. Earth’s magnetic field forms (shielding against the solar wind) |
| 3.8–3.5 billion years ago | The first life | Prokaryotes (bacteria and archaea) appear at deep-sea vents or in shallow seas. Fossils: Isua, Greenland (3.8 billion) and stromatolites in Western Australia (3.5 billion). LUCA, the last universal common ancestor of all life |
| 3.0–2.7 billion years ago | Photosynthesis begins | Cyanobacteria split water and release oxygen. Iron in the oceans absorbs it first, forming banded iron formations — most of today’s iron ore |
| 2.4–2.1 billion years ago | Great Oxidation Event | Oxygen accumulates in the atmosphere → poison to most anaerobic life of the time. Methane breaks down and the greenhouse collapses → the Huronian glaciation, the first Snowball Earth |
| 2.0–1.8 billion years ago | Eukaryotes | Cells with a nucleus and mitochondria (a swallowed bacterium turned partner — endosymbiosis). Chloroplasts arise the same way later |
| 1.8–0.8 billion years ago | The “Boring Billion” | The supercontinent Rodinia forms (1.1 billion). A stable stretch with slow evolutionary change |
| 1.2 billion years ago | Sexual reproduction | Red algae fossils. Genetic recombination speeds up evolution |
| 720–635 million years ago | Snowball Earth (Cryogenian) | Ice reaches the equator. Volcanic CO₂ builds up and thaws it → a surge of nutrients |
| 635–539 million years ago | Ediacaran | The first large multicellular organisms (the Ediacaran biota) — soft-bodied, strange forms without mouths or guts. Most vanish before the Cambrian |
- Life appeared within a billion years of Earth’s formation, but stayed single-celled for the next 3 billion years. Complex life exists only in the last 600 million years of Earth’s history.
- Oxygen is a product of life — the 21% oxygen in the atmosphere is a by-product of photosynthesis, and most of what we breathe is made by phytoplankton in the oceans.
The Paleozoic — the explosion of life and the move onto land
539–252 million years ago. The era that begins in the sea and climbs onto land.
| Period | Span (years ago) | Representative life | Events |
|---|---|---|---|
| Cambrian | 539–485 million | Trilobites, Anomalocaris, Pikaia (the first chordate) | The Cambrian explosion — most modern animal phyla appear within 20 million years. Eyes, shells and predation arrive. Burgess Shale (Canada), Chengjiang (China) |
| Ordovician | 485–444 million | Graptolites, nautiloids, the first fish (jawless) | Marine life diversifies. First traces of land plants (mosses). Mass extinction ① at the end (glaciation; 85% of species lost) |
| Silurian | 444–419 million | Sea scorpions, jawed fish | Vascular plants colonize land (Cooksonia). The first land animals (millipedes, scorpion-like arthropods) |
| Devonian | 419–359 million | Placoderms (Dunkleosteus), lungfish, Tiktaalik | “The age of fishes”. The first forests (Archaeopteris). Fish → tetrapods (Tiktaalik 375 million, Ichthyostega). Mass extinction ② in the late Devonian |
| Carboniferous | 359–299 million | Giant ferns, Lepidodendron, Sigillaria; Meganeura (a dragonfly with a 70 cm wingspan); the first reptiles (amniotes) | Vast swamp forests → coal (Coal · oil). Oxygen at 35% (21% today) lets insects grow huge. The amniotic egg lets reptiles breed away from water |
| Permian | 299–252 million | Dimetrodon (a synapsid — the lineage leading to mammals), Lystrosaurus | The supercontinent Pangaea is complete; interiors dry out. Mass extinction ③ at the end — the largest ever (Siberian Traps volcanism; 96% of marine species). “The Great Dying” |
- Order of colonizing land: plants (440 million) → arthropods (420 million) → vertebrates (370 million). Plants had to go first to provide food and oxygen before animals could follow.
- Mammals descend not from dinosaurs but from the Permian synapsids, which ruled the land before the dinosaurs, were pushed aside after the extinction, and survived 200 million years in small bodies.
The Mesozoic — the age of dinosaurs
252–66 million years ago. Begins in the wreckage of the end-Permian extinction and ends with an asteroid.
| Period | Span (years ago) | Representative life | Events |
|---|---|---|---|
| Triassic | 252–201 million | The first dinosaurs (Eoraptor, 230 million), the first mammals (225 million, shrew-sized), pterosaurs, ichthyosaurs | Recovery after the extinction. Pangaea begins to break up. Mass extinction ④ at the end (volcanism as the Atlantic opens) — with their rivals gone, dinosaurs take over the land |
| Jurassic | 201–145 million | Brachiosaurus and Diplodocus (sauropods), Allosaurus, Stegosaurus, Archaeopteryx (150 million) | The dinosaur heyday begins. Pangaea → Laurasia and Gondwana. Warm and humid; conifers and cycads. Dinosaurs → birds branch off. In the sea: plesiosaurs, ammonites |
| Cretaceous | 145–66 million | Tyrannosaurus, Triceratops, Velociraptor, Mosasaurus, the first snakes | Flowering plants (angiosperms) appear and spread (130 million) → co-evolution with insects, bees. Continents approach their modern positions. Marsupials and placentals diverge. Mass extinction ⑤ at the end — asteroid impact (Chicxulub, Mexico, 10 km across) + Deccan Traps volcanism in India → all non-avian dinosaurs die out |
- Dinosaurs ruled for 165 million years — 66 times the 2.5 million years of the genus Homo. Tyrannosaurus is further in time from Stegosaurus (80 million years) than from us (66 million).
- Dinosaurs did not go extinct — birds are dinosaurs (descendants of theropods). Today’s 10,000 bird species outnumber the 6,000 mammal species.
- Plankton of the Jurassic and Cretaceous seas is the main source of today’s oil (Coal · oil).
The Cenozoic — mammals and apes
66 million years ago to the present. Mammals fill the space the dinosaurs left, and primates emerge at the end.
| Period · epoch | Span (years ago) | Events |
|---|---|---|
| Paleogene — Paleocene | 66–56 million | After the dinosaurs, mammals diversify rapidly and grow large. The first primates (plesiadapiforms) |
| Paleogene — Eocene | 56–33.9 million | PETM (55.6 million) — abrupt warming; crocodiles and palms at the poles. The ancestors of whales (Pakicetus) return to the sea. Ancestors of horses and elephants. India collides with Asia → the Himalayas begin to rise |
| Paleogene — Oligocene | 33.9–23 million | Antarctica isolated and glaciated → global cooling. Grasslands spread. Monkeys and apes diverge |
| Neogene — Miocene | 23–5.3 million | The heyday of apes (Proconsul, Sivapithecus). Grasslands expand; horses, cattle and antelope evolve. Human and chimpanzee lineages split (c. 7 million) |
| Neogene — Pliocene | 5.3–2.58 million | The Isthmus of Panama forms (2.8 million) → animals cross between the Americas; Atlantic currents shift → northern glaciation begins. Australopithecus (Human evolution) |
| Quaternary — Pleistocene | 2.58 million–11,700 years | The ice ages. Glacials and interglacials alternate on a ~100,000-year cycle (Milankovitch cycles). Mammoths, sabre-toothed cats, woolly rhinos. The genus Homo appears and spreads; Homo sapiens emerges |
| Quaternary — Holocene | 11,700 years ago–present | Warm, stable climate after the last glacial. Agriculture, civilization and all of recorded history fall within it. Megafauna extinctions (human impact). The “Anthropocene” proposed |
- Throughout the Cenozoic the planet has been cooling — from the Eocene hothouse to the Quaternary ice ages. Main causes: the rise of the Himalayas (rock weathering draws down CO₂) and the isolation of Antarctica.
- We live in an interglacial (the Holocene) of an ice age. Geologically, the Quaternary ice age has not ended.
The Five Mass Extinctions
Five events in the 540 million years of the Phanerozoic in which 75% or more of species disappeared. The usual cause is massive volcanism (CO₂ and sulphur → abrupt climate change and ocean acidification); an asteroid did it only once, the last time.
| # | When (years ago) | Name | Cause | Result |
|---|---|---|---|---|
| ① | 445 million | End-Ordovician | Gondwana drifts over the South Pole → glaciation, sea level plunges | 85% of species lost. Mostly marine life |
| ② | 372 million | Late Devonian | Spread of land plants → eutrophication and anoxia of the seas / volcanism proposed | 75% of species. Reefs and placoderms vanish |
| ③ | 252 million | End-Permian (“The Great Dying”) | Siberian Traps — 2 million years of lava, 10 °C warming, ocean acidification and anoxia | 96% of marine species, 70% of land vertebrates — the largest ever. Trilobites gone for good. Recovery takes 10 million years |
| ④ | 201 million | End-Triassic | Volcanism of the Central Atlantic Magmatic Province (Pangaea breaking up) | 80% of species. Dinosaurs’ rivals (crocodile relatives etc.) removed → the dinosaur heyday |
| ⑤ | 66 million | End-Cretaceous (K-Pg) | Asteroid impact (Chicxulub) — impact winter, wildfires, acid rain + Deccan Traps volcanism | 75% of species. Non-avian dinosaurs, pterosaurs and ammonites vanish. The age of mammals opens |
| (⑥) | Now | Holocene (ongoing) | Humans — habitat destruction, overhunting, climate change | Extinction rates 100–1,000 times the background rate. The “sixth mass extinction” debate |
- Mass extinctions were destruction and opportunity at once. Without ③ there might have been no dinosaurs; without ⑤, no age of mammals — and no us.
- Evidence for the K-Pg boundary: a worldwide iridium layer (an element abundant in asteroids; the Alvarezes, 1980) → the Chicxulub crater identified beneath Yucatán in 1991.
When coal, oil and natural gas were made
All three are the remains of ancient life, buried away from oxygen and subjected to heat and pressure for tens to hundreds of millions of years. The raw material and the timing differ.
| Fuel | Raw material | Main period of formation | Why then |
|---|---|---|---|
| Coal | Land plants — trees and ferns of swamp forests | Concentrated in the Carboniferous–Permian (360–250 million years ago); also Jurassic, Cretaceous and Paleogene coalfields | In the vast tropical swamps of the Carboniferous, dead trees piled up without rotting. The leading idea: trees had only just evolved lignin (wood), and fungi able to digest it did not yet exist, so the wood was buried intact for tens of millions of years → peat → lignite → bituminous coal → anthracite. With so much CO₂ locked in the ground, oxygen rose to 35% and an ice age set in. |
| Oil | Marine plankton (algae and microbes) — not dinosaurs | About 70% of world reserves formed in the Jurassic–Cretaceous (200–66 million years ago); also Permian and Devonian fields | Plankton flourished in warm, shallow seas (the Tethys — today’s Middle East); organic matter settled on anoxic seabeds and became shale (source rock). Buried 2–4 km deep, at 60–120 °C (the “oil window”), the kerogen turns into oil. Hotter, and it becomes gas |
| Natural gas | The same material as oil, or coal | Same periods as oil; deeper and hotter | Above 120 °C organic matter breaks down into methane. Shale gas is what stayed trapped in the source rock |
- Fossil fuels are a record of carbon buried over geologic time. Carbon that the Carboniferous took 300 million years to bury, humanity is returning to the atmosphere in about 200 years — that is the essence of climate change.
- Why the Middle East has so much oil: in the Mesozoic it was the warm, shallow continental shelf of the Tethys Sea, and later continental collisions folded the rocks into anticlines that trap oil.
- The “lignin hypothesis” — that coal formation dropped off once fungi evolved — is debated (tectonics and climate are also emphasized), but the Carboniferous is nonetheless the age of coal.
Human Evolution — from Australopithecus to Homo sapiens
The lineage after the split from chimpanzees in Africa about 7 million years ago. It is a bush, not a line — many species lived at the same time, and most are our cousins rather than our direct ancestors. As recently as 20–30,000 years ago there were several human species on Earth.
| Species | Lived (years ago) | Region | Traits · significance |
|---|---|---|---|
| Sahelanthropus tchadensis | 7 million | Chad | A candidate from just after the split from chimpanzees. Foramen magnum beneath the skull → possibly upright |
| Ardipithecus ramidus | 4.4 million | Ethiopia | “Ardi”. Walked on two legs in woodland and still climbed — bipedalism came before the savanna |
| Australopithecus afarensis | 3.9–2.9 million | East Africa | “Lucy” (3.2 million, found 1974), the Laetoli footprints (3.66 million). Brain 400 cc (chimpanzee-sized), 1 m tall, fully bipedal. A candidate ancestor of the genus Homo — an upright “ape-man” stage rather than “the first human ancestor” |
| Australopithecus africanus | 3.3–2.1 million | Southern Africa | The Taung Child (1924, Dart) — the first evidence that humans originated in Africa |
| Paranthropus | 2.7–1.2 million | East and South Africa | Massive molars and jaws for tough plant food. A side branch — died out without descendants |
| Homo habilis | 2.4–1.4 million | East Africa | “Handy man”. Brain 600–700 cc. Oldowan stone tools (the oldest tools, 3.3 million years old at Lomekwi, are of unknown maker). The genus Homo begins |
| Homo erectus | 1.9 million–110,000 | Africa → Eurasia | “Upright man”. Brain 900–1,100 cc, modern body proportions, long-distance running. Acheulean hand axes (1.7 million). Use of fire (1 million–400,000). The first to leave Africa (1.8 million) — Java Man, Peking Man (700,000–400,000). Lasted 1.7 million years — the longest-lived human species |
| Homo heidelbergensis | 700,000–200,000 | Africa · Europe | Brain 1,200 cc. Big-game hunting with wooden spears (Schöningen, 300,000). The likely common ancestor of Neanderthals and sapiens |
| Homo neanderthalensis | 400,000–40,000 | Europe · western Asia | Brain 1,500 cc (larger than ours), stocky cold-adapted build. Burials, ornaments, fire, composite tools. Interbred with sapiens — 1–2% of the DNA of people outside Africa. Gone by 40,000 years ago |
| Denisovans | 300,000–50,000 | Siberia · East Asia | A species known in 2010 only from the DNA of a finger bone. Tibetans’ high-altitude gene and about 5% of Melanesian DNA are Denisovan |
| Homo floresiensis | 100,000–50,000 | Flores, Indonesia | The “hobbit”. 1 m tall, brain 400 cc. Island dwarfism |
| Homo naledi | 335,000–236,000 | South Africa | Found in 2015. Small brain (500 cc) yet contemporary with sapiens. Debated evidence of placing the dead in a cave |
| Homo sapiens | 300,000–present | Africa → worldwide | Jebel Irhoud, Morocco (300,000); Omo, Ethiopia (195,000). Brain 1,350 cc, rounded skull, a chin. The only surviving human species |
- Is Australopithecus the first ancestor of sapiens? The usual reading of the direct line is: some African australopith (afarensis is the favourite) → Homo habilis → erectus → heidelbergensis → sapiens, but every arrow is debated. What is certain is that every step happened in Africa.
- Were the Neanderthals killed off by sapiens? There is no evidence of massacre. The likely explanations: (1) competition with sapiens’ greater numbers, technology and social networks, (2) climate swings, (3) absorption of a minority into sapiens groups (interbreeding). Since they survive in our genes, “completely gone” is not quite right.
- The order of evolution: bipedalism (7–4 million) → stone tools (3.3–2.5 million) → brain expansion (2 million–) → fire (1 million) → language and symbols (300,000–70,000). We walked first; the big brain came much later.
Homo sapiens — from the Cognitive Revolution to civilization
Sapiens appeared 300,000 years ago and lived for more than 200,000 years without leaving much of a mark — then, from about 70,000 years ago, something changed. The end of this table is the beginning of the World History notes.
| When (years ago) | Event | What happened |
|---|---|---|
| 300,000 | Sapiens appears | The “pan-African” view — evolving in several parts of Africa at once — is now favoured |
| 120,000–100,000 | First exit from Africa (failed) | Reached the Levant (Skhul and Qafzeh, Israel), then died out or withdrew |
| 70,000 | The Cognitive Revolution | Yuval Harari’s term. A qualitative leap in language — the ability to speak of and believe in things that do not exist (myths, gods, tribes, rules) → cooperation among hundreds or thousands of strangers. Archaeologically, “behavioural modernity”: engraved ochre and beads at Blombos Cave (75,000), refined tools, long-distance trade. The cause — a genetic mutation, population density — is unsettled |
| 74,000 | Toba eruption | A supervolcano in Sumatra — the “volcanic winter” may have cut humanity to a few thousand (the bottleneck hypothesis, debated) |
| 70,000–60,000 | Out of Africa (successful) | Via the southern Red Sea or Sinai into Arabia → the whole world. Everyone outside Africa descends from this small group |
| 65,000 | Reaching Australia | They crossed open sea — the first evidence of boats. Giant marsupials go extinct |
| 50,000–45,000 | Entering Europe | Coexistence and interbreeding with Neanderthals → Neanderthals vanish (40,000) |
| 40,000–17,000 | Upper Paleolithic art | Chauvet (36,000), Lascaux (17,000), Altamira. Venus figurines, bone flutes, the Lion Man (40,000) — they carved beings that exist only in the imagination. |
| 30,000–15,000 | Domestication of the dog | From the wolf. The first domestic animal |
| 26,000–19,000 | Last Glacial Maximum | Sea level 120 m lower. The Bering land bridge exposed |
| 20,000–15,000 | Entering the Americas | Across Beringia → the Clovis culture (13,000). Mammoths, mastodons and other megafauna go extinct |
| 11,700 | The Holocene begins | The last glacial ends; the climate stabilizes — the precondition for farming |
| 11,500 | Göbekli Tepe | Turkey. A monumental temple built before agriculture — the idea that religion and communal ritual drew people into settlement and farming |
| 12,000–10,000 | The Agricultural (Neolithic) Revolution | The Fertile Crescent (wheat, barley, goats, sheep; c. 10,000 BC) → the Yangtze (rice, 8000 BC) and Yellow River (millet) → Mesoamerica (maize, 7000 BC) → the Andes (potato) → New Guinea (taro). Invented independently in at least 7–10 places. Settlement, population growth, private property, class, epidemic disease, longer working hours — Harari calls it “history’s biggest fraud” |
| 9000–7000 BC | The first towns | Jericho (9000 BC, walled), Çatalhöyük (7000 BC, 5–8,000 people). Pottery came earlier — Jōmon Japan (14,000 BC) and China. |
| 5000–3500 BC | Copper Age · the wheel · irrigation | Copper smelting (5000 BC); the wheel, the plough and the sailing ship (3500 BC); irrigation farming in Mesopotamia → surplus → city-states |
| 3300 BC | The Bronze Age | Copper + tin = bronze. Begins in the Near East → Europe, the Indus, China (c. 2000 BC), Korea (1500–1000 BC). Bronze is scarce, so it goes to weapons and ritual vessels → a ruling class forms |
| 3200 BC | Writing — from prehistory to history | Sumerian cuneiform; Egyptian hieroglyphs (3100 BC). Here the World History notes take over. |
| 1200 BC | The Iron Age | The Hittites first (1500 BC–), then widespread after the Bronze Age collapse (1200 BC). Iron is plentiful, so tools and weapons reach everyone → social upheaval. China c. 600 BC, Korea c. 300 BC |
- Paleolithic → Neolithic → Bronze Age → Iron Age is a division by tool material (Thomsen, 1836). Paleolithic = chipped stone (3.3 million–12,000 years ago, 99% of human history); Neolithic = polished stone + farming + pottery; then metals. The dates differ by region — Korea: Paleolithic from 700,000 years ago (Jeongok-ri, Yeoncheon), Neolithic 8000 BC (comb-pattern pottery), Bronze Age 1500–1000 BC (Gojoseon), Iron Age 300 BC.
- Harari’s three revolutions: the Cognitive Revolution (70,000 years ago) → the Agricultural Revolution (12,000 years ago) → the Scientific Revolution (500 years ago). The first set sapiens apart from the other human species, the second made civilization, the third made the modern world.
- The Cosmic Calendar (Carl Sagan): compress 13.8 billion years into one year and the Solar System forms on August 31, life appears on September 21, the Cambrian explosion is December 17, the dinosaurs December 25–30, the genus Homo arrives at 10:30 p.m. on December 31, agriculture at 11:59:32 p.m., and all of recorded history fills the last 14 seconds.