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An Evolutionary Timeline

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Image: Carnegie Museum of Natural History


Archaean, 3.5 billion - 2.5 billion years ago
Single-celled bacteria form in the seas.

Proterozoic, 2.5 billion to 544 million years ago
Multicellular organisms such as algae develop.
Soft-bodied animals follow hundreds of millions of years later.


Cambrian, 544 million to 505 million years ago
Marine invertebrates, such as trilobites, dominate.

Ordovician, 505 million to 440 million years ago
The first vertebrates, such as primitive, jawless fish, form.

Silurian, 440 million to 410 million years ago
Fresh water fish and the first fish with jaws appear.
Animals and plants make the move to land.

Devonian, 410 million to 360 million years ago
The first forests and land-dwelling vertebrates form.

Mississippian, 360 million to 325 million years ago
Coal deposits begin.
Sharks and large primitive trees develop.

Pennsylvanian, 325 million to 286 million years ago
The first reptiles appear.
Insects and fern forests spread.

Permian, 286 million to 245 million years ago
In the largest mass extinction ever recorded, most marine invertebrates die off.


Triassic, 245 million to 208 million years ago
Survivors spread and re-colonize.

Jurassic, 208 million to 146 million years ago
The age of the dinosaurs.
The first mammals appear around 200 million years ago, and the first birds take to the sky.

Cretaceous, 146 million to 65 million years ago
Flowering plants appear.
Mass dinosaur extinctions begin.
The earliest known placental mammal, the mouse-sized Eomaia, appears around 125 million years ago.


Tertiary, 65 million to 1.8 million years ago
The first primates evolve around 55 million years ago, followed by the first human-like creatures.

Quaternary, 1.8 million years ago to today
Modern humans -- Homo sapiens -- appear around 200,000 years ago.

Sources: Universtiy of California, Berkley Museum of Paleontology/ American Geological Institute