Putting Time into Proportion

These time scales are drawn to scale so you can compare the relative lengths of geologic time divisions.

4,550,000,000 years of geologic time

All of Earth history is represented in this time scale. Notice the immense amount of time that passed prior to the explosion of life that took place at the beginning of the Phanerozoic Eon, about 570 million years ago.

Click on time periods to see reconstructions of ancient Earth.

Close-up: The Phanerozoic Eon

Now we've narrowed our view down to just the last 570 million years. The Phanerozoic Eon
is subdivided into three Eras, the Paleozoic, Mesozoic, and Cenozoic. The Eras are further
broken up into Periods. Notice that even at this scale, the Cenozoic Era, also known as the
" Age of the Mammals", is only a tiny portion of Earth history.

Click on time periods to see reconstructions of ancient Earth.

Close-up: The Cenozoic Era

Here's a close-up look at the last 66.4 million years. If you are wondering where us humans are,
take a look at the Holocene Epoch. The Holocene Epoch began about 10,000 years ago and
continues to the present. Virtually all written human history occurred in the Holocene, yet, at this
scale, 10,000 years is such a brief period that it too small to draw! The entire record of human
history would be narrower than a single pixel on your computer screen!

Click on time periods to see reconstructions of ancient Earth.

Close-up: The Pleistocene and Holocene Periods

This time scale shows the Pleistocene and Holocene Epochs. The Pleistocene is commonly
known as "The Ice Age". The Holocene Epoch includes all recorded human history. These two
Epochs span just the last 1.6 million years.

Click on time periods to see reconstructions of ancient Earth.

More geologic time resources

More information on how we know the age of the Earth and how rocks are dated.
Click here to download a PDF version of this geologic time scale and other resources.

For more information on geologic time, why not visit one of these USGS sites?

Geologic Time on-line
Fossils, Rocks, and Time

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This page was last updated on 01/13/04