A series working through the 4.6 billion years of Earth’s history, one interval at a time. Each article follows what happened in that age, and what remains unknown about it.
Laying them out side by side makes one thing plain: how unevenly the time is distributed. The Phanerozoic, in which life can be traced through fossils (from the Cambrian onward), covers about 540 million years — while the Precambrian before it covers about 4 billion. Nearly 90 percent of Earth’s history falls within the first three eons. In the list below, too, the entries near the top handle overwhelmingly longer spans of time.
Precambrian (about 4,567 to 539 million years ago)
The Hadean (about 4,567 to 4,031 million years ago)
A surface covered in magma, and the giant impact that made the Moon. An age from which not a single rock survives.
【Earth Timeline 01】The Hadean Eon – An Age With No Surviving Rock
The Archean (about 4,031 to 2,500 million years ago)
The earliest traces of life, and how far back they can be pushed.
【Earth Timeline 02】The Archean Eon – When Traces of Life Began to Appear
The Proterozoic (about 2,500 to 539 million years ago)
Oxygen accumulates in the atmosphere, the whole planet freezes over, and the first large organisms appear in the sea.
【Earth Timeline 03-1】The Proterozoic Eon – How the Atmosphere Filled With Oxygen
【Earth Timeline 03-2】The Proterozoic Eon – A Planet Frozen to the Equator, and the First Large Life
Paleozoic (about 539 to 252 million years ago)
The Cambrian (about 539 to 487 million years ago)
The basic designs of animal bodies come together within a short span.
【Earth Timeline 04】The Cambrian Period – When the Blueprints of Animal Bodies Came Together
The Ordovician (about 487 to 443 million years ago)
Seas full of reefs, and abrupt cooling at the end.
【Earth Timeline 05】The Ordovician Period – Reef-Filled Seas and an Ending Locked in Ice
The Silurian (about 443 to 419 million years ago)
What plants had to solve in order to come ashore.
【Earth Timeline 06】The Silurian Period – When Plants Came Ashore
The Devonian (about 419 to 359 million years ago)
How the fins of fish turned into legs for walking on land.
【Earth Timeline 07】The Devonian Period – How Fins Became Legs
The Carboniferous (about 359 to 299 million years ago)
Forests of giant ferns, and dragonflies with wingspans near 70 cm. Why could insects grow so large?
【Earth Timeline 08】The Carboniferous Period – Giant Insects and Oxygen-Rich Forests
The Permian (about 299 to 252 million years ago)
The continents gather into one, and then the largest extinction in Earth’s history occurs.
【Earth Timeline 09-1】The Permian Period – When the Continents Became One
【Earth Timeline 09-2】The Permian Period – The Greatest Extinction in History
Mesozoic (about 252 to 66 million years ago)
The Triassic (about 252 to 201 million years ago)
The new cast that moved into an emptied world. Dinosaurs were still bit players.
【Earth Timeline 10】The Triassic Period – Filling the Seats Left Empty by Extinction
The Jurassic (about 201 to 143 million years ago)
The age when dinosaurs grew large and took the lead on land.
【Earth Timeline 11】The Jurassic Period – When Dinosaurs Took the Lead on Land
The Cretaceous (about 143 to 66 million years ago)
The spread of flowering plants and feathered dinosaurs. And the day the asteroid fell.
【Earth Timeline 12-1】The Cretaceous Period – When Flowers Bloomed and Feathers Spread
【Earth Timeline 12-2】The Cretaceous Period – The Day the Asteroid Hit
Cenozoic (66 million years ago to the present)
The Paleogene (66 to about 23 million years ago)
The age when mammals filled the empty seats. Abrupt warming, and the ancestors of whales returning to the sea.
【Earth Timeline 13-1】The Paleogene Period – A World Where Mammals Filled the Empty Seats
【Earth Timeline 13-2】The Paleogene Period – Abrupt Warming and the Whales That Returned to the Sea
The Neogene (about 23 to 2.58 million years ago)
Grasslands spread, and the Mediterranean dries out for a time.
【Earth Timeline 14】The Neogene Period – When the Mediterranean Dried Up
The Quaternary (about 2.58 million years ago to the present)
Glacials and interglacials in repetition. This is the period in which Homo sapiens appeared.
【Earth Timeline 15-1】The Quaternary Period – Why Mammoths Vanished in the Last Ice Age
【Earth Timeline 15-2】The Quaternary Period – When Earth Had Many Human Species
On reading order
Every article is written to stand on its own, so you can start anywhere. The idea is to enter at whichever age interests you and come back to this index when you want to know what came before or after.
Dates in each article follow the International Chronostratigraphic Chart published by the International Commission on Stratigraphy (ICS): International Chronostratigraphic Chart (ICS)
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