What is the Geologic Time Scale?

The Earth’s crust consists of many layers of rock (strata) and Geologists assume each layer represents a long period of time, typically millions of years. These layers contain billions of fossils, some unique to certain layers. The layers are arranged by Geologists into order that assumes macro-evolution. This theory is not without scientific objection and argument, as is the case with many scientific assumptions. You can find more information here: