1. Earth’s History
According to science, Earth formed 4.6 billion years ago.
About the same time that our Solar System formed.
Geologic Time: The time of the physical formation and development of Earth.

2. Geologic Timeline What would this timeline look like?
Geologic Timeline: a tool used by geologists to organize events that have occurred on Earth.
The timeline is commonly split up into Eras, Periods and Major Events.

3. Telling Time
Absolute Time: the actual date of an event or age of an animal.
A fossil of an organism can be aged to a specific year(s).
Example: First trilobites existed 521 MYA
Relative Time: the sequencing of events, the order in which things happened.
What came first, second, third, fourth, etc.
Example: Cyan Bacteria, Trilobite, Ratfish, Raptor, Woolly Mammoth

4. Fossils Trilobite is Wisconsin’s state fossil.
What does this tell you about the environment of Wisconsin 521 MYA?
Fossils: the preserved remains or traces of plants, animals, and other organisms
They give us clues on how the environment conditions and organisms have changed over time.

5. Paleontologist: A scientist that specializes in studying fossils.
Examples: Bones, Footprints, Shells

6. Fossil Records
Fossil Record: a set of fossils that have been discovered, that provide clues about Earth’s history.

7. Law of Superposition
Law of Superposition: layers of rock near the surface are younger, layers farther from the surface are older.
How is this related to the age of fossils?

8. Uniformitarianism
Theory of Uniformitarianism: Earth has always been changing and will continue to change over time due to natural events like, weathering and other natural disasters.
What is the evidence?

9. Eras of Time
Very large units of time that begin and end with specific major events.
4 Eras
Precambrian Era (OLDEST)
Paleozoic Era
Mesozoic Era
Cenozoic Era (PRESENT DAY

10. Precambrian Era
Represents 4 billion years of Earth’s history. (Largest Era)
Started with Origin of Earth
Ended with Marine Invertebrates (Boneless water creatures) appearing on Earth

11. Precambrian Era (continued)
Major Events Include
- Beginning of Earth
- First Cells Appear (no nucleus)
- No Free Oxygen in Air
- Cyan Bacteria Produces Oxygen (poisonous)
- Oxygen accumulate and cells start using it.
- Complex cells appear (with nucleus)
- Multi-cellular plants and animals appear
- Marine invertebrates appear

12. Paleozoic Era Represents about 300,000,000 years of Earth’s history.
Started with Earliest Fish Appear
Ended with First Reptiles Appear

13. Paleozoic Era (continued)
Major Events Include
-Earliest Fish Appear
-Oxygen reaches 20% (current level)
-First Amphibians appear
-Trees Appear
-First reptiles appear

14. Mesozoic Era “Age of Reptiles”
Represents about 200,000,000 years.
Started with First Dinosaurs Appear
Ended with Extinction of Dinosaurs

15. Mesozoic Era (continued)
Major Events Include
- First Dinosaurs Appear
- First Mammals Appear
- Extinction of dinosaurs

16. Cenozoic Era “Age of Mammals”
Represents about 65,000,000 years
Started with Birds Appearing
Has not ended because we are part of this Era.
What could possibly end our Era we are living in?

17. Cenozoic Era (continued)
Major Events Include
- Birds Appear
- Flowering Plants Appear
- Human Like Forms Appear
- Homo Sapiens appear

18. A Snapshot of Earth’s History

19. Very Slow Changes
Evolution: the adaptations of living things to change overtime so they can survive. This happens very slowly.
Example: Wooly Mammoth and an Elephant.
Any other animals you can think of?

20. Charles Darwin
Charles Darwin: Developed the theory of natural selection when he visited the Galapagos Islands.
How might an iguana adapt to living on an island?
He found iguana like lizards that have adapted to living on the island. Because of this adaptation, these creatures were able to reproduce and pass on their genes.

21. Why would animals change?
Theory of Natural Selection: species that are best adapted to their environment are more likely to survive and pass on their traits.
Adaptation: a change that an animals makes in order for them to survive in their current environment.

22. Extinction of Animals Two Reasons Endangered Animals
Competition between species. (meat eating dinosaurs)
Catastrophic Events (Natural Disasters)
Endangered Animals