GEOLOGIC TIME The Earth is about 4.6 billion years old. Earth’s history is divided into time units that make up a geologic time scale. These sections of time are divided according to major events geologists believed occurred according to the rock and fossil record.

Some of these major events include: 1. Mass extinctions 2. Ice Ages 3. Domination of different types of animals like dinosaurs and mammals 4. Mountain building events due to plate movement

DIVIDING UP GEOLOGIC TIME There are four major divisions of time 1. Eon: longest division of time 2. Era: Eons are subdivided into Eras 3. Periods: Eras are subdivided into Periods 4. Epoch: Periods are subdivided into Epochs (shortest time division)

NOW Eon: Two major eons: Precambrian: takes up 88% of Earth’s 4.6 billion years Phanerozoic: the eon we live in LONG AGO

This is today Geologic Time Line 3 Major Eras PreCambrian Makes Up 88% Of Earth’s History Earth is formed 4.6 bya

NOW Era: three major eras: Paleozoic (“ancient life”) Mesozoic (“middle life”)—dinosaurs dominated this era Cenozoic (“recent life”)--we live in this Era LONG AGO

NOW 3. Period: we live in the Quaternary Period LONG AGO

4. Epoch: The Cenozoic is the only era subdivided because of knowing a lot about this era since we live in it We live in the Recent or Holocene Epoch

Human history is extremely brief Human history is extremely brief. If you think of the entire history of Earth as one year, the first multicellular organisms would have appeared in September. The dinosaurs would have disappeared at 8 PM on December 26th. Modern humans (like us) would not have appeared until 11:48 PM on December 31st.

AMAZING EARTH SCIENCE FACTS: 1. The shortest time division is the __________. 2. The longest time division is the ___________. 3. We live in the _________________ era. 4. We live in the _________________ epoch. 5. We live in the _________________ period. 6. Precambrian time makes up _____ of Earth’s history. epoch eon Cenozoic Recent Quaternary 88%

A B