Scientists have divided geologic history into 4 main parts:

1. Eras of the Geologic Time ScaleScientists have divided the Earth’s history into 4 major parts: the Geologic Time scale Scientists have divided geologic history into 4 main parts: Precambrian Time Paleozoic Era Mesozoic Era Cenozoic Era

2. Precambrian Time • 4.6 billion – 543 million years ago • Life began during this time • Atmosphere made of water vapor, CO2 & N2 • Volcanic eruptions, meteorites, violent storms & intense solar radiation

3. Origin of Life? • Extraterrestrial • Life came from outside the planet(i.e. meteor) • Creation • Divine forces created life • Non-Living Matter • Spontaneous assembly of molecules

4. 4 billion years ago - Earth began to cool Water condensed and fell as rain

5. Atmosphere of early Earth • Hydrogen (H2) • Volcanic gas (i.e. methane (CH4), ammonia (NH3), CO, SO2, N2, CO2) • No free oxygen or ozone

6. UV • Energy stimulated chemical reactions + = Proteins Nucleic Acids Lipids Carbohydrates

7. How Did Life Begin? • In the oceans • Energy from radiation and storms caused simple chemicals in the oceans & atmosphere to react • More complex molecules were made • Molecules joined to form cells • Prokaryotes: single-celled organisms (without a nucleus) that did not need O2 to survive

8. Photosynthesis & Oxygen • Cyanobacteria (type of prokaryotic organism) appears over 3 bya • Uses sunlight to produce food

9. Photosynthesis & Oxygen • Oxygen gas is released into oceans & air • Oxygen molecules react to form Ozone, which absorbs harmful radiation form the sun • Now possible for life to exist on Earth’s surface

10. Photosynthesis & Oxygen • VOCs • Volatile organic compounds • NOx • Nitrogen-oxygen compounds

11. Multicellular Organisms • Eukaryotes appear in the fossil record • Organism that contain a nucleus • Will evolve into organisms composed of many cells

12. Paleozoic Era (543 – 248 mya) • “Old life” or “Ancient life” • Large fossil record • Sponges, coral, squid, clams, trilobites, fish, sharks • Reptiles, amphibians, fish, worms, & ferns first appear

13. Paleozoic Era – Life on Land • Plants, fungi, & air-breathing animals slowly colonized land • Crawling insects first animals to live on land • Reptiles & winged insects appear near the end of era • LARGEST Mass extinction marks end of era • 90% of species extinct • Oceans completely changed

14. Mesozoic Era (248 – 65 mya) • “Middle Life” or “Age of Reptiles” • Dinosaurs dominate Earth for 150 million yrs • First birds appear • Conifers appear • Flowering plants appear late in era

15. End of Mesozoic Era • Mass Extinction • Dinosaurs • Many other plant & animal species • Meteorite hit Earth • Dust, smoke, fires • Temperatures dropped for many years

16. Cenozoic Era (65 mya – today) • “Recent Life” or “Age of Mammals” • Many mammals, birds, insects & flowering plants • Saber-toothed cats, camels, small horses

17. Cenozoic Era Today • Era we are currently living in • Climate changed many times during era • Periods of ice ages • Animals migrate, adapt, or become extinct