Geology Reference
In-Depth Information
the events that have occurred and life forms that have existed (and faded from existen-
ce) in the history of the earth.
First I explain how scientists determine the age of rocks using radioactivity and strati-
graphic relationships (the relationships among various layers of rock). Then I describe
how earth's history is organized into eons, eras, and periods using the geologic time
scale. And finally, I take you layer by layer through the story of earth, describing the
geologic events and the evolution of organisms from single cells, to dinosaurs, to you
and me.
