Geologic time periods (eons, eras, periods, epochs)

Using the various techniques of estimating the age of given rock layers and finding particular kinds of fossils in given rock layers, geologists have constructed a “motion picture” of how the Earth itself and life forms on it have changed (evolved) over the billions years of its history.  Key features are described in the following illustrated lecture:

A chart giving geologic time periods and key life forms of those period is given here:

http://www.rocksinmyheadtoo.com/TimeLine.htm