Geologic Time (Part 4)
Geologic Time Scale
• The first geologic time scale was based on the relative ages of sedimentary rock units recognized in Europe. For example, Cambrian and Devonian rocks were named for places in Great Britain. Newer geologic time scales use absolute age dates to put ages in years on time scale units.
• The present geologic time scale divides the history of the earth into eons, eras, periods, and epochs.
• The oldest rocks in Virginia are 1.1 billion years old. They are metamorphic rocks in the Blue Ridge and Piedmont. The youngest rocks in Virginia are forming today as soils, river sediments, and shoreline deposits.
Click on each part of the geologic time scale.
(Color scheme based on that of the U.S. Geological Survey; diagrams by Phyllis Newbill, modified by Jon Tso)