The History of Life on Earth

A mass extinction occurs when a large number of species go extinct during a relatively short amount of time.

The largest division of the geologic time scale is the era.

We currently live in the Cenozoic era.

Fossils show that the first living things were very tiny.

Scientists develop hypotheses about Earth's history based on observable changes in the _.

(a)  

Endangered species are protected by law in an effort to preserve them from _.

(a)  

A _ is a trace or imprint of a living thing that is preserved by geological processes.

(a)  

All of the fossils that have been discovered worldwide make up the _.

(a)  

_ dating determines whether a fossil formed before or after another fossil.

_ dating estimates the age of a fossil in years.