Geologic Time Scale

The geologic time scale is a giant timeline that organizes major events such as the evolution of life, climate changes, and mass extinctions.

Life on Earth started with tiny, simple, single-celled organisms. Over billions of years, they evolved into protists, fungi, plants, and animals.

The evidence for this transformation is found in fossils and rocks.

Fossils tell us what kinds of creatures lived in the past. For example, the discovery of fossilized dinosaur bones reveals the existence of these magnificent creatures.

Rock layers also help figure out the order in which different species appeared.

By examining the sequence of rock layers and the fossils they contain within them, scientists can reconstruct the relative timeline of when various species emerged and disappeared throughout Earth's vast geological history.

Using data from fossils, rock formations, and lunar samples brought back by the Apollo missions, scientists estimate that the Earth is at least 4.5 billion years old.