1. GEOLOGIC TIME
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2. Geologic Time Scale
Paleontologists have divided Earth’s history into time units based on life forms that lived only during certain periods.
If no fossils were present, divisions were based on other criteria.

3. Major Subdivisions of Geologic Time
Oldest rocks have no fossils but later they appeared sparsely. Even later there was a huge explosion of life and diversity.
From Largest to smallest- 1) Eons- longest subdivisions; based on certain fossils
2) Era- marked by major, worldwide changes in fossils
3) Periods- characterized by types of life existing worldwide at that time
4) Epoch- characterized by life forms but vary from continent to continent. Instead of names, some are called early, middle, late.

5. Important Events in Geologic Time
Hadean Eon- 1) 4.5 million years ago-Origin of Earth 2) first life form
Ordovician Period-1st fish
Silurian Period- 1st land plants
Devonian Period- 1st amphibians
Mississippian Period- 1st reptiles
Triassic period- mass extinction and Pangaea breaks apart
Jurassic Period- 1st birds

6. Events Continued
Cretaceous Period- 1st flower plants- ends with mass extinction
Pliocene Epoch- begins with rise of Himalayas
Currently we are in the Phanerozoic Eon, Cenozoic Era, Quaternary Period and Holocene Epoch

7. Early Life- Precambrian
Cyanobacteria or Blue-green algae- Through photosynthesis, their oxygen changed the Earth’s atmosphere and created an ozone layer.
This paved the way for invertebrates-organisms with no backbone- left trace fossils only

8. Paleozoic Life
Vertebrates appeared and some moved to land. Some of them had both gills and lungs. Todays lungfish still has both. They are thought to be ancestors of amphibians.

9. Theories of Mass Extinction
Mountains formed creating desert areas and animals could not adapt
Volcanic Activity changed atmosphere
Asteroid collided with Earth

10. Evolution- idea that species have changed over time.
Organic Evolution
Charles Darwin
Evolution- idea that species have changed over time.
Natural Selection- organisms suited to an environment have a better chance of survival and reproduction.
Survival of the Fittest- organisms reproduce more than can survive so they compete for resources. Only the strongest survive and reproduce

11. EVOLUTION of Humans (1 theory)
The 3.2-million-year-old ape "Lucy" was the first Australopithecus afarensis skeleton ever found, though her remains are only about 40 percent complete
With a mixture of ape and human features— including long dangling arms but pelvic, spine, foot, and leg bones suited to walking upright— slender Lucy stood three and a half feet (107 centimeters) tall.

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