Earth is approximately 4.5 billion years old. That is a really big number, written like this: 4,500,000,000.

How long do you think it would it take to count to one billion? If you start counting one number a second without stopping until you reach a billion, it will take you 31 years, 259 days, 1 hour, 46 minutes, and 40 seconds!

It might seem like the earth stays still, and we are the ones dancing on top of it. While we do grow, change, and move much faster than our planet does, the earth dances too! But you have never seen a dance so slow, to music we cannot hear!

The earth moves and changes very slowly, slower than we can ever imagine. Geological time (or earth time) is measured by time periods of varying lengths. From the longest to the shortest, these are called eons, eras, periods, and epochs. The "Precambrian Eon" which ended when complex life began, lasted 4 of the 4.5 billion years of the earth's history!

Here is a definition of those geological time words:

Eon - A division of time made up of two or more eras
Era - A division of time composed of several periods.
Period - A division of time shorter than an era and longer than an epoch.
Epoch - A unit of geological time that is a division of a period and is characterized by rock formations.

Each of these measuring units does not have an exact number of years, but are measured by changes in the rock formations that tell scientists when certain events happened in the earth's history. Radiological dating methods help scientists to figure out the approximate number of years that passed between each change.

Take a look at our geological clock below, and see what the earth may have looked like at different points in its history. Notice that modern man has only been around for 10,000 years, less than a second on the geological clock! ROLLOVER TEXT on diagram below with your mouse and see more information. You can also click on underlined text to launch a map on 6 out of 10 of these links!

For more information, see Plate Tectonics related topic!