Geologic Time Scale

• Geologic time scale is a record of the life forms and geologic events in Earth’s History

• Written from present to past– Opposite of many of

our timelines that we are used to

Precambrian Time•Geologic time begins with

Precambrian time•Covers about 88% of Earth’s history•Ended 544 million years ago (mya)•After Precambrian time, the basic

units of geologic time scale are eras, periods and epochs

Paleozoic Era•Began about 544 mya•Lasted for 300 million years•Paleo means ancient or early, zoic means life

•Most animals were invertebrates

Mesozoic Era•Began about 245 million years ago•Lasted about 180 million years•Meso means middle•Often called the Age of Dinosaurs•Mammals began evolving in this

era

Cenozoic Era

•Began about 65 million years ago

•Continues today•Ceno means recent•Called the age of mammals

Periods• Eras are

subdivided into periods

• Range in length from tens of millions of years to less than 2 million years

Epoch• Periods of the

Cenozoic Era are divided into epochs– The fossil record

of the Cenozoic Era is more complete so it makes it easier to divide it further

Reflection page 46•Compare your personal

timeline (“This is Your Life” Activity) with Earth’s timeline. What similarities and differences do you see?