What is geologic Time Scale? How we describe the history of the Earth.

What are the two ways we decide how old something is (dating)? Relative&Absolute

How do we know there was life in the past? Fossils

What does extinction mean? A species stops existing.

Four time scale periods Eon (largest) EraPeriodEpoch

There are four EONs HadeanArcheanProterozoicPhanerozoic

Major events cause breaks in these units Growth of life end of life.

The first three Hadean, Archean, &Proterozoic Called the Precambrian time Life is only in the ocean. From the beginning to 540 million years ago

The Phanerozoic EON This is the EON now. Began about 540 millions years ago. Has three ERAs (paleozoic, mesozoic, & cenozoic)

#1: Paleozoic Era Complex life began to exist. 540 to 250 million years ago. Began with the Cambrian explosion. Ended with the Permian extinction.

#A: Cambrian Explosion Many many new life forms developed. They were more complex.

#B: Permian Extinction Most species on earth went extinct. 70 to 90% of the species.

#2: Mesozoic Era 250 to 65 million years ago Called the Time of the lizards. This is when Dinosaurs ruled. Began with the Permian extinction Ended with the K-T extinction

#3: Cenozoic Era 65 millions years ago to today Called the Time of the Mammals. Began with K-T extinction.

Home work Homework page 297 #5.a.b. & Vocab Prepare for the quiz Tomorrow