The story before people: from the Big Bang 13.8 billion years ago to the end of the last Ice Age, when the Inventions timeline takes over.
The whole universe we can see was once squeezed into something hotter and denser than anything today, and it has been expanding ever since. In the first few minutes, the first atoms’ centers formed: hydrogen and helium. What came before the Big Bang, if anything, is still unknown.
For about 100 million years the universe was dark. Then gravity pulled clouds of hydrogen and helium together until they grew hot enough to shine: the first stars. They were huge and short-lived, and when they exploded, they made the first heavier elements, like carbon and oxygen.
Stars gathered into galaxies, including ours. The Milky Way has grown since by swallowing smaller galaxies, and now holds 100 to 400 billion stars. From a dark place, like the hills of Nepal on a moonless night, you can see it as a glowing band across the sky.
A cloud of gas and dust, with elements made in earlier stars, collapsed and began to spin. Most of it became the Sun; the rest formed a flat disk around it, where dust clumped into rocks and rocks into planets. The iron in your blood and the calcium in your bones were made in stars before the Sun.
The Earth grew from rocks crashing together around the young Sun. At first it was a ball of molten rock, too hot for oceans. Heavy iron sank to the center to make the core, and lighter rock floated on top.
A body about the size of Mars probably crashed into the young Earth, and the debris thrown into space came together as the Moon. Rocks brought back by the Apollo astronauts are very like the Earth’s, which supports the idea. The Moon was much closer then and looked far bigger in the sky.
Tiny crystals of zircon from the Jack Hills in Australia, the oldest bits of Earth ever found, formed about 4.4 billion years ago. Their chemistry shows that there was already liquid water on the surface. The Earth had cooled enough for oceans surprisingly early.
Rocks in Australia hold stromatolites, layered mounds built by mats of microbes, at least 3.5 billion years old; some scientists think life began even earlier. How life started is one of the great unanswered questions. Living stromatolites, like these at Shark Bay, still grow in a few salty bays.
Tiny blue-green microbes, cyanobacteria, had learned to use sunlight to make food, giving off oxygen. At first rocks soaked it up, but about 2.4 billion years ago oxygen began to build up in the air. For many microbes it was a poison; for later life, it made breathing and big bodies possible.
A new kind of cell appeared, bigger and with its DNA kept in a nucleus. Its power stations, mitochondria, were once separate bacteria that came to live inside it. Every plant, animal and fungus, including you, is made of this kind of cell.
Living things made of many cells working together, such as a red seaweed found in Canada called Bangiomorpha, appeared by about a billion years ago. Cells began to take on different jobs. This happened several separate times, in seaweeds, fungi, plants and animals.
Ice spread from the poles almost to the equator, perhaps covering the whole planet, for millions of years. Volcanoes slowly filled the air with carbon dioxide until the Earth warmed and the ice melted. Soon after, the first large animals appeared.
Soft, flat creatures lived on the sea floor, some shaped like quilted mats or fronds, up to more than a meter long. Many are unlike any animal alive today. One, Dickinsonia, was shown to be an animal by traces of fat-like molecules in its fossils.
Within a few tens of millions of years, a short time in Earth’s history, the seas filled with animals with shells, eyes, legs and jaws. Most of the main body plans of animals alive today, from worms to the ancestors of fish, appear in the fossils of this time.
Small, fish-like animals such as Haikouichthys, found in China, had a skull and the beginnings of a backbone. They were only a few centimeters long and had no jaws. Every fish, frog, bird and mammal, including us, descends from animals like them.
The first land plants were small and low, like today’s mosses and liverworts, growing near water. They broke rock into soil and changed the air. Insects, spiders and other small animals soon followed them out of the water.
An ice age suddenly lowered the seas and changed the oceans, and about 85% of the kinds of sea life died out. It was the first of five great mass extinctions. Some scientists think the way people are changing the Earth today is causing a sixth.
Trees appeared, some like giant ferns, up to about 8 meters tall. Their roots broke up rock and made deep soil, and the forests pulled carbon dioxide from the air. The oldest fossil forest found is in New York State, USA.
Tiktaalik, found in the Canadian Arctic in 2004, was a fish with a neck, lungs and strong front fins with wrist-like bones. It could prop itself up in shallow water. Animals like it led to the first four-legged animals on land, the ancestors of frogs, reptiles, birds and mammals.
The moving plates of the Earth’s crust pushed all the main continents together into one supercontinent, Pangaea, surrounded by one ocean. It began to break apart about 200 million years ago, and the pieces are still moving, about as fast as your fingernails grow.
Small lizard-like animals such as Hylonomus, found inside fossil tree stumps in Canada, laid eggs with tough shells that would not dry out. Unlike frogs, they no longer needed water to breed. Reptiles, birds and mammals all come from such animals.
Huge swampy forests covered much of the land, and the air had more oxygen than today. Insects grew bigger than any alive now: Meganeura, a dragonfly-like hunter, had wings about 70 cm across. The coal burned today is mostly the remains of these forests.
Enormous volcanic eruptions in Siberia poured out lava and gases for hundreds of thousands of years, heating the planet and making the oceans acidic. About 90% of sea life and most life on land died out, the worst extinction in Earth’s history. It took millions of years to recover, and the survivors included the ancestors of dinosaurs and mammals.
The first dinosaurs, found in Argentina and Brazil, were small, fast animals that ran on two legs, about the size of a dog. Over the next 30 million years they spread across the world and grew into the biggest animals that ever walked on land.
Small, furry animals the size of a shrew appeared, probably active at night to stay away from dinosaurs. They fed their young on milk, like all mammals today. For more than 150 million years, mammals stayed small while dinosaurs ruled.
Small feathered dinosaurs related to Velociraptor, such as Archaeopteryx, could flap or glide. Birds come from dinosaurs like these, so birds are living dinosaurs. Many dinosaurs had feathers, not for flying at first, but probably for warmth and display.
Flowering plants appeared and spread quickly, along with the bees, butterflies and other insects that carry their pollen. Today almost 90% of the kinds of plants on land have flowers, including the rice, wheat and maize that feed most people.
India had once been joined to Africa, Antarctica and Australia. After it split away, it raced north across the ocean, up to about 15 cm a year, faster than any continent moves today. In between, it passed over a hot spot that poured out huge lava flows, the Deccan Traps.
An asteroid about 10 km wide hit what is now Mexico, throwing so much dust and soot into the air that the Sun was dimmed for years. About three-quarters of all kinds of plants and animals died out, including all the dinosaurs except birds. With them gone, mammals spread into every kind of life.
A huge release of carbon into the air warmed the Earth by 5 to 8 °C over a few thousand years, and it took about 200,000 years to cool down. Scientists study it to understand today’s warming, which is adding carbon to the air about ten times faster.
India crashed into Asia and kept pushing, crumpling and lifting the rock between them. That is how the Himalaya, and Nepal’s landscape, were made, and India is still pushing north about 4 to 5 cm a year, which is why Nepal has earthquakes. The summit of Mount Everest is made of limestone that formed at the bottom of a sea, full of fossils of sea creatures.
Pakicetus, found in Pakistan, looked like a wolf-sized animal with hooves and a long tail, but its ears had the special bones of a whale. Whales and dolphins come from land animals like it, which moved back into the water over about 10 million years. Their closest living relatives are hippos.
As carbon dioxide in the air fell and Antarctica became surrounded by a cold ocean current, ice began to cover it. Today its ice sheet is up to almost 5 km thick and holds about 60% of the world’s fresh water. If it all melted, the seas would rise about 58 m.
Our lineage split from that of chimpanzees, our closest living relatives. Sahelanthropus, found in Chad, may be one of the first in our line; its skull suggests it held its head over its body, as animals that walk upright do. Walking on two legs came long before big brains.
The Mediterranean Sea had been cut off from the Atlantic and had nearly dried up, leaving thick layers of salt. Then the Atlantic broke through at Gibraltar, and, in one idea of how it happened, refilled the whole sea in a few months to two years, in a flood far bigger than any river.
The Earth entered a time of repeating ice ages, with ice sheets spreading over North America and Europe and then melting back, again and again, about every 100,000 years in the last million. Himalayan glaciers grew far longer than today. We are living in a warm spell between ice ages.
Homo erectus, a human species with long legs and a body much like ours, was the first to spread out of Africa, as far as Georgia, China and Java. It survived for almost two million years, longer than our own species has existed so far.
Neanderthals lived in Europe and western Asia through the ice ages. They had big brains, buried their dead, made tools and jewelry, and cared for injured people. They died out about 40,000 years ago, but not completely: most people today carry a little of their DNA.
The oldest known fossils of our species, from Jebel Irhoud in Morocco, are about 300,000 years old. Early Homo sapiens lived in many parts of Africa. For most of our history, we shared the Earth with other kinds of humans.
A volcano on Sumatra, in Indonesia, had one of the biggest eruptions of the last few million years. It left a lake 100 km long, and its ash fell as far away as India. How much it cooled the world and harmed people is still argued about.
Groups of modern humans left Africa and, within about 15,000 years, reached South Asia, Southeast Asia and Australia, crossing the sea by boat. Everyone outside Africa today descends mostly from these travelers.
The Denisovans were a human species known mostly from a finger bone, teeth and DNA, found in a cave in Siberia and on the Tibetan Plateau. Modern humans met and had children with them. A gene from the Denisovans helps many Tibetans and Sherpas live well high in the Himalaya, where there is less oxygen.
Ice sheets up to 3 km thick covered Canada and northern Europe, and so much water was locked in ice that the sea was about 120 m lower than today. People could walk from Asia to North America, and from Britain to Europe.
The Earth warmed, the great ice sheets melted, and the sea rose. The climate became steadier than it had been for a long time, and soon after, people in several parts of the world began to farm. The Inventions timeline carries on from here.
Dates this old are worked out from rocks, fossils, and the light of distant stars, so they are rounded and change a little as scientists learn more. Each entry links to where you can read more, and some to the discovery that told us about it.
The Big Bang: NASA/WMAP Science Team, Public domain · Our galaxy, the Milky Way, begins: ESO/Yuri Beletsky, CC BY 4.0 · The Sun is born: NASA/JPL-Caltech, Public domain · The Moon forms: NASA/JPL-Caltech, Public domain · The first oceans: Wikimedia Commons, CC BY-SA 3.0 · The first life: Paul Harrison, CC BY-SA 3.0 · Snowball Earth: Oleg Kuznetsov - 3depix - http://3depix.com/, CC BY-SA 4.0 · The first large animals: Verisimilus at English Wikipedia, CC BY 2.5 · The first forests: Eduard Solà, CC BY-SA 3.0 · Fish with legs: Zina Deretsky , National Science Foundation, Public domain · Pangaea, one giant continent: Scotese, Christopher R.; Vérard, Christian; Burgener, Landon; Elling, Reece P.;…, CC BY 4.0 · Eggs with shells: Natural History Museum, London, modified by Jason D. Pardo, Kendra Lennie & Jason S.…, CC BY 4.0 · Giant insects: Gaëlle Doitteau & Sandra DAILLIE, CC BY 4.0 · India sets off for Asia: Alataristarion, CC BY-SA 4.0 · The asteroid that ended the dinosaurs: NASA/Don Davis, Public domain · Whales walk: Kevin Guertin from Ottawa, Ontario, Canada, CC BY-SA 2.0 · Walking on two legs: Didier Descouens, CC BY-SA 4.0 · The Mediterranean refills: Paubahi, CC BY-SA 3.0 · The Ice Ages begin: Hannes Grobe /AWI, CC BY 3.0 · Leaving Africa: Eduard Pop et al., CC BY 4.0 · The Neanderthals: Ryan Schwark, CC0 · The Toba supereruption: Anynobody, CC BY-SA 4.0 · People spread around the world: NordNordWest, Public domain · The Denisovans, and the gift of high altitude: Fu et al. (2025), CC BY 4.0
