Ages of the Earth

The Earth formed 4750 million years ago(mya) but the first animals with shells and bones appeared less than 600 mya. It is mainly with the help of their fossils that geologists have learned about the Earth's history since then. We know very little about the 4000 million years before, known as Precambrian Time.

Just as days are divided into hours and minutes, so geologists divide the Earth's history into time periods. The longest are eons, thousands of millions of years long. The shortest are chrons, a few thousand years long. In between come eras, periods, epochs and ages.

The years since Precambrian Time are split into three eras: Paleozoic, Mesozoic and Cenozoic. Different plants and animals lived at different times, so geologists can tell from the fossils in rocks how long ago the rocks formed. Using fossils, they've divided the Earth's history since Precambrian Time into 11 periods. To see the ages of the Earth click here.

By the beginning of the Permian, the motion of the Earth's crustal plates had brought much of the total land together, fused in a supercontinent known as Pangea. Most of the rest of the surface area of the Earth was occupied by a corresponding single ocean, known as Panthalassa, with a smaller sea to the east of Pangea known as Tethys. Below you can see how the current continents were formed.