Geologic maps are an important part in discovering the world's age and the history behind rock structures created on Earth.  Hopefully this page will help you understand some basic concepts of geologic maps.  This web page was created for Earth Science Lab ES111DA, at Emporia State University with reference from Susan Aber and Introduction To Earth Science Lab.

What are Geologic maps?  Geologic maps are a symbolic representation of the absolute age of different rock formations that are outcropping on the surface of the Earth.  Geologic maps reveal the subsurface geology by using the rules of tectonic features, relative position in sequence, and the absolute age of rock formations. (45)

How is the age of rock classified?  Every rock is classified into four major time units called Eras: Cenozoic, Mesozoic, Paleozoic, and Precambrian, from youngest to oldest.  An era is subdivided into rock systems or periods; systems can be divided into series or epochs; series can be subdivided into groups and groups into formations.  Rock units are named for the area they were first describe in and mapped as formations and groups of formations based on the fossil content or by absolute dating methods. These rock units can be identified in widely separated places around the world, correlating the age and fossil contents.  Any one geologic map will only list the time periods found in the area covered by the map, not all possible units in the world. (45) The Geologic Time Scale is shown to the right. The classifications, associated ages, and occurrences of flora and fauna are shown. Geologic maps are difficult to read for some who have never seen one. Therefore, a set of rules was made to guide you in this process: rules for interpreting features on geologic maps.

This figure was taken from: http://www.clearlight.com/~mhieb/WVFossils/GeolTimeScale.html.

Aber, S. W., Johnston, P., Morales M., & Sleezer, R. Introduction To Earth Science Lab (5th Ed.)   Edina, Minnesota:  Burgess International Group, Inc., 2000: 45

Geologic Time Scale.  Hieb, Monte & Hieb, Harrison. September 1999.  28 March 2000, http://www.clearlight.com/~mhieb/WVFossils/GeolTimeScale.html.