Article

Introduction
The Two maps
Zoom In
Features
Legend and Rock Ages
Rock Types
Political Boundaries
Credits

Ages in Millions of Years

Here, we've divided the time scale into its four major components: the Cenozoic era, the Mesozoic era, the Paleozoic era and the Precambrian. Since Cenozoic is the most recent of these it is at the top-left. Precambrian, being the oldest, is at the bottom.

The time scale is further divided. For example, the Mesozoic, the age of the dinosaurs, is made up of the Cretaceous, Jurassic, and Triassic periods.

The numbers on the scale indicate commonly accepted age boundaries of these eras. The Precambrian stretches from the origin of the earth, more than 4 billion years ago, to 540 million years ago (or mega anna, MA). The Paleozoic from 540 MA to 248 MA. Mesozoic covers the interval between 248 and 66 MA. Cenozoic covers the span from 66 MA to the present.

As you can see, the time scale is not drawn linearly, which is why the Precambrian, which lasts over 3.5 billion years, appears shorter than the Paleozoic, which lasted a little more than 290 million years.