1. GEOLOGIC TIME “History of the Earth”

2. Learning Targets
2a) I can distinguish between eons, eras, periods, and epochs (DOK 1). 2b) I can identify the order of the eras and the relative length of the eras (DOK 1). 2c) I can identify key geological and biological features of the 4 different eras (DOK 1).

3. Essential Question
How is Earth’s history organized?

4. How Old is the Earth?
About 4.6 billion years old

5. 4.5 bya-Solar System Forms (Nebular Hypothesis)
How was Earth formed?
13.7 bya-BIG Bang
Explosion of atomic particles
Cooling to form clouds of H and He
Star formation Galaxies Clusters
4.5 bya-Solar System Forms (Nebular Hypothesis)
Solar nebula (rotating cloud dust/gas)
Planetesimals (clumps formed in spinning disk of matter)
8 Protoplanets & moons
Early Earth impact moon

6. How is Earth’s History organized?
Scientist use fossils and other clues to organize the events in Earth’s history into a timeline.
Geologic time is organized into lengths of time based on life forms present and events such as extinctions.
There are 5 mass extinctions that scientist know about throughout history.
-Cretaceous-Tertiary (KT) extinction, 65 mya- Killed the dinosaurs.
- Permian-Triassic (PT) extinction, 251 mya– Killed about 95 % of all species.

7. When were the mass extinction events?
Time Frame (mya)
Types of Life Effected
Late/End Ordovician
443 mya
Many species of Trilobites, Brachiopods, Graptolites, Echinoderms and Corals
Late/End Devonian
354 mya
Many marine families on tropical reefs, Corals, Brachiopods, Bivalves, Sponges
Late/End Permian
248 mya
57% of all marine families, Trilobites, Eurypterids, Mollusca devastated along with Brachiopods. Many vertebrates
Late/End Triassic
206 mya
Mollusca phyla, Sponges, marine vertebrates, large amphibians, many mammal-like reptiles
Late/End Cretaceous
65 mya
Ammonites, Marine reptiles, dinosaurs, pterosaurs, microscopic marine plankton, Brachiopods, bivalves, and echinoderms

8. What are the Divisions of Geologic Time?
Geologic time is divided into:
Eons
Eras
Periods
Epochs

11. What are the Four Eras?
Precambrian Era ( mya) Longest era, bacteria-like life forms present.

12. What are the Four Eras?
2. Paleozoic Era ( mya) Broken down into 7 periods. 1st plants, fish, reptiles, amphibians, and insects.

13. What are the Four Eras?
3. Mesozoic Era ( mya) Broken down into 3 periods. Era of the dinosaurs and first mammals and birds.

14. What are the Four Eras?
4. Cenozoic Era (65 mya – present) 2 periods, mammals are abundant. Homo sapiens evolve.

15. Check for Understanding
Write a paragraph that covers the following:
How Earth was formed
How Earth’s history is organized
The divisions of time that is used for Earth’s history
A summary of the four eras