The Geological History of Earth

4.5 billion years in a single story

A Planet Is Born (4.5–4.0 Billion Years Ago)

Earth formed around 4.5 billion years ago from a swirling cloud of gas and dust orbiting our young Sun. Early Earth was a molten, cratered world, constantly bombarded by asteroids and so hot that rock existed as liquid. The Moon formed during this period, likely from the debris of a Mars-sized body that collided with the young Earth.

Gradually, Earth cooled. A solid crust formed. Water vapor released from volcanic eruptions condensed to form the first oceans. The Hadean Eon, named for its hellish conditions, slowly gave way to something more habitable.

The First Life and the First Continents (4.0–1.0 Billion Years Ago)

By around 3.5 billion years ago, microbial life had appeared, the oldest fossils we have found are stromatolites, layered mounds built by ancient cyanobacteria. These early organisms would transform the planet: over hundreds of millions of years, they pumped oxygen into the atmosphere, causing the Great Oxidation Event around 2.4 billion years ago.

During this vast span, the first tectonic plates formed and began their endless shuffling. The supercontinent Columbia (or Nuna) assembled around 1.8 billion years ago, then broke apart. Rodinia followed, assembling roughly 1.1 billion years ago.

Snowball Earth and the Cambrian Explosion (750–485 Ma)

Around 700–635 million years ago, Earth may have frozen almost entirely, a dramatic hypothesis called Snowball Earth. Ice reached to the tropics. Eventually, volcanic CO₂ accumulated enough to warm the planet back, and the ice melted in a geologically sudden thaw.

The aftermath set the stage for the Cambrian explosion, beginning around 541 million years ago. In a geological blink, nearly all major animal body plans appeared, trilobites, mollusks, echinoderms, the earliest vertebrates. Complex, multicellular, mobile life had arrived.

The Road to Pangea (480–250 Ma)

For the first 300 million years of the Phanerozoic, Earth's continents slowly converged. Gondwana, comprising what would become Africa, South America, Antarctica, Australia, and India, was the dominant landmass. To the north, smaller continents like Laurentia and Baltica collided to form Laurussia.

The Devonian period saw forests colonize the land and tetrapods begin their conquest of dry ground. The Carboniferous was an age of vast coal swamp forests. By the Permian, Gondwana and Laurussia had merged into a single landmass: Pangea, stretching from pole to pole.

Pangea and the Great Dying (300–200 Ma)

Pangea was a world of extremes. The vast interior of the supercontinent, far from any ocean, was a scorching desert. Life adapted to this harsh geography: the first true reptiles evolved, able to lay eggs and live entirely away from water.

The Permian period ended in catastrophe around 252 million years ago. A massive volcanic event, the Siberian Traps, poured millions of cubic kilometers of lava over Siberia and pumped enormous quantities of CO₂ and sulfur dioxide into the atmosphere. Up to 96% of marine species and 70% of land vertebrates went extinct.

The Breakup of Pangea (200–66 Ma)

Life recovered, slowly. The Triassic period saw the rise of dinosaurs and the first mammals. And Pangea began to tear apart. By the Jurassic, a rift had split Pangea into Laurasia in the north and Gondwana in the south. The Atlantic Ocean began to open as North America pulled away from Africa and Europe.

By the Cretaceous, the southern continents were separating too. Then, 66 million years ago, an asteroid roughly 10 kilometers across struck near Chicxulub, Mexico. The impact triggered wildfires, tsunamis, and a global winter. Three-quarters of all species perished, including all non-avian dinosaurs.

The Modern World Takes Shape (66 Ma – Present)

In the aftermath, mammals flourished and diversified explosively into whales, bats, horses, elephants, and primates. India collided with Asia around 50 million years ago, crumpling the crust into the Himalayas. The Americas connected across the Isthmus of Panama around 3 million years ago.

In this cold, fragmented world, a particular primate lineage in Africa evolved language, fire, and tools. Modern humans spread out of Africa roughly 70,000 years ago and reached every continent within tens of thousands of years.

What Comes Next?

The continents are not done moving. The Atlantic Ocean is still widening. The Pacific is slowly closing. In roughly 50 million years, Africa will collide with Europe, closing the Mediterranean. In 250 million years or so, the continents may reassemble into a new supercontinent, sometimes called Pangea Proxima or Amasia, completing another cycle in the endless rearrangement of Earth's surface.