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?