Geologic Time

Geologic time is used by paleontologists and geologists to make sense of the vast expanse of time in the history of the earth. We are talking about 4.5 billion years! In order to put this all in perspective geologic time uses divisions and sub-divisions. The major divisions are called Eons. On the charts below there are 4 eons, The Hadean, Archaean, Proterozoic, and Phanerozoic. Each eon is divided into Eras, the eras are divided into Periods, and the Periods are divided into Epochs. 

Everyone of these time divisions has characteristics that are unique and identify a stage in the earth's long history. 

We have 2 charts below to help you visualize some if the relationships of geologic time. To read the charts remember that the oldest times are at the bottom of the charts. More recents times show up closer to the top. 

Learning the age of your fossils is part of the fun of being a collector. The age of fossils is given as a number of million years ago or as a Period in the history of the earth such as the Jurassic Period. A paleontologist tries to visualize an environment to help understand a fossil. You can learn a lot about the geography, climate, and other plants and animals that existed at the time a fossil was a living thing.

The first Geologic Time Chart below has 3 sections. In the center are the names of the eons, eras, and periods paleontologists and geologists use to talk about geologic history. The most recent times are near the top of the chart. As we go toward the bottom of the chart we are going back farther and farther into the earth's history.

The left side is a simplied look at the evolution of life. It follows the center section starting at the bottom and moving forward in time toward the top. The lines represent groups of related animals.  The right side of the chart lists some of the major events in earth's history, again starting at the bottom.

Chart 2

In this chart the names of each Eon, Era or Period are linked to pages that contain information on the geology, biology, and climate of that particular time. Simply click on the name of the time division for more detailed information about it.

Note: At the upper right of the chart is a section labled Old Periods. Like all of the sciences our understanding changes as we learn more. The names and times of these divisions are modified as we learn more about the history of the earth. Not too long ago the names of the periods of the Cenozoic Era were changed as noted on the chart.