OneofthefirstscientiststounderstandgeologictimewasJamesHutton. Inthelate1700s, he
traveled around Great Britain and studied sedimentary rocks and their fossils. He believed
that the same processes that work on Earth today formed the rocks and fossils from the
past. He knew that these processes take a very long time, so the rocks must have formed
over millions of years. Before Hutton, most people believed the Earth was only several
thousand years old. His work helped us understand that the laws of nature never change
and that the Earth is very old. He is sometimes called the “father of geology.”
The geologic time scale is often shown with illustrations of how life on Earth has changed. It
sometimesincludesmajoreventsonEarth, too, suchastheformationofthemajormountains
or the extinction of the dinosaurs.Figure12.2shows you a different way of looking at the
geologic time scale. It shows how Earth’s environment and life forms have changed.
Figure 12.2: A different way of looking at the Geologic Time Scale. ( 1 )Lesson Summary
- The Earth is very old, and the study of Earth’s past requires us to think about times
that were millions or even billions of years ago. Scientists use the geologic time scale
to illustrate the order in which events on Earth have happened. - The geologic time scale was developed after scientists observed changes in the fossils
going from oldest to youngest sedimentary rocks. They used relative dating to divide
Earth’s past in several chunks of time when similar organisms were on Earth. - Later, scientists used absolute dating to determine the actual number of years ago
that events happened. The geologic time scale is divided into eons, eras, periods, and
epochs.