Scroll through the timeline at left to learn about some of the major events in Earth's history -- from present to 4.8 billion years ago.

230 thousand years ago
The first Homo sapiens (upright humans) evolved.

3.5 million years ago
Evidence of the oldest human ancestors date from this time.

20 million years ago
Large mammals increase in importance. Grasslands and deserts form in the middle of continents.

65 million years ago
Dinosaurs go extinct. Pangea has broken up into present day continents. The Rocky mountains form.

100 million years ago
Flowering plants appeared. Tyrannosaurus rex roamed the earth.

160 million years ago
The first mammals evolved. This is the oldest age of the Pacific crust.

200 million years ago
Dinosaurs, including the giant long-necked sauropods, ruled the earth. Sharks, ichthyosaurs, and giant marine scorpions ruled the seas.

245 million years ago
The largest mass extinction ever claimed most of the marine organisms. Most of the land on Earth is contained in the single supercontinent, Pangea.

300 million years ago
Lush swamps known as “coal swamps” covered the land. The Appalachian Mountains formed when the continents Godwanaland and Laurasia collided.

440 million years ago
Fish and coral reefs spread through the oceans. Plants and animals, including relatives of spiders and centipedes, colonized the land.

520 million years ago
A huge number of new animals evolved, including the first animals with hard skeletons. Trilobites were abundant.

560 million years ago
The first animals evolved. These animals had soft bodies and lived in the oceans.

1.8 billion years ago
The first eukaryotic cells (cells with nuclei) appeared.

2.2 billion years ago
Oxygen levels in the atmosphere increased dramatically.

3.5 billion years ago
The first life appeared. Colonies of photosynthetic bacteria formed hard calcium carbonate mounds called stromatolites.

3.8 billion years ago
The oldest rocks date from this time.

4.8 billion years ago
The solar system, including the planet Earth, was born.