2. Warm up
Draw a picture or describe what you think earth looked like 4 billion years ago

3. Change through Time: The History of Life

4. Earth’s Early Conditions
Inhospitable living Conditions
Volcanic Activity
Lots of molten lava
Earth was VERY hot (How hot was it?)
No atmosphere initially
No water
Lots of ultraviolet radiation (no ozone layer)

5. Earth’s Early Conditions
Volcanic gasses given off:
H2 -- hydrogen
N2 -- nitrogen
H2 O vapor
CO and C02
NH 4 -- ammonia
CH4 -- methane

6. Changes in Earth’s History
Weather began after the atmosphere built up from volcanic gasses.
Torrential rains from water vapor built up
Filled up Earths basins to become bodies of water
Caused erosion

7. Changes in Earths History
Plate tectonics
(Pangaea – all continents)
Supercontinent began to break apart and move around Earth
Mountain formation
Earth cooled down
Several Ice ages occurred

8. Earths Present Conditions
Atmosphere
N2 ≈ 70%
O2 ≈ 21%
Misc. ≈ 9%
Water 70% of surface
Land 30% of surface

9. Earths Present Conditions
Weather and climate varies around the world according to latitude.
Earthquakes and volcanoes occur occasionally
Lots of Life (great biodiversity)

10. Important Dates 15 Billion years ago (BYA) – Universe formed
4.6 BYA – Earth formed
3.9 BYA Earth cooled and oceans formed
3.5 BYA – first life appeared

11. Eras of Earths History Precambrian ( 3.4 BYA) - 87% of Earths history
- oldest evidence of life found in Precambrian rock
Prokaryotic → no nucleus
Eukaryotic → have a nucleus
By the end of this era, the oceans were filled with multicellular organisms like algae, sponges and jellyfish.

12. Paleozoic - Lasted until 248 million years ago (MYA)
During the Cambrian Period there was a great increase in biodiversity
(E.g. - worms, echinoderms, arthropods, fish, ferns, reptiles, amphibians)
Mass extinction at the end of the Paleozoic.
90% of marine spp. And 70% of land spp. gone forever.

13. Mesozoic Era Divided into 3 periods:
Triassic – 1st mammals (they were tiny then) and 1st dinosaurs
Jurassic – the “age of dinosaurs”
Cretaceous – more mammals and flowering plants (E.g. – oak, fig, and elm trees)

14. Cenozoic Era Began 66 MYA This is the era in which we live
Primates evolved → we belong to this group of mammals
Modern human spp. Evolved about 200,000 YA

15. Over 90% of the species that have lived on Earth are now extinct → consider how biodiverse the Earth would be had they not died off…

16. Answer the following questions
Describe what Earth was like before life arose.
Make a table listing the four major divisions of the geologic time scale, their time spans, and the major life forms that appearing during each interval.