Earth Science 8.5 The Geologic Time Scale – Flashcards

A record of the life forms and geologic events in Earth's history.

The three long units between Precambrian Time and the present

Subdivisions of eras

Animals without backbones

Animals with backbones

Animal that lives part of it's life in water and parts of it's life on land.

Animals with scaly skin that lay eggs with tough, leathery shells

When many types of living things became extinct at the same time

A warm blooded vertebrate that feeds it's young milk

Because the time span of Earth's past is so great, geologists use the geologic time scale to show Earth's history.

But scientists have found fossils of single celled organisms in rocks that formed about 3.5 billion years ago. These earliest life forms were probably similar to present day bacteria.

In the beginning of the Paleozoic Era, many different kinds of organisms involved. Reptiles were so successful during the Mesozoic Era that this is sometimes called the Age of Reptiles. The extinction of dinosaurs created an opportunity for mammals. During the Cenozoic Era, mammals evolved to live in many different environments - on land, in water, and even in the air.