1. Early Earth:

2. I. Ch 12, Sec 1 - Is Earth Unique?

3. I. Ch 12, Sec 1 - Is Earth Unique?
The Right Planet
If Earth was much larger, it would have more gravity and a thick, nasty atmosphere of lighter gases such as Ammonia, Methane, Hydrogen and Helium.

4. I. Ch 12, Sec 1 - Is Earth Unique?
The Right Planet
If Earth was much smaller, it would have less gravity – Oxygen and water vapor would escape into space and there would be no life on Earth!

5. I. Ch 12, Sec 1 - Is Earth Unique?
The Right Planet
3) If Earth didn’t have a plastic (“gooey”) layer of mantle below its rigid crust, there would be no plate tectonics, no continental crust and mountains. Earth’s entire surface would be fairly flat and completely covered by a shallow ocean.

6. I. Ch 12, Sec 1 - Is Earth Unique?
The Right Location
1) If Earth was 10 % closer to the Sun, the extra heat would drive oxygen and nitrogen into space, leaving behind mostly heavier carbon dioxide. Earth would be too hot and oxygen-poor for higher life forms to thrive.

7. I. Ch 12, Sec 1 - Is Earth Unique?
The Right Location
If Earth was 10% farther away from the sun, it would be so cold that the ocean would freeze over.
(No liquid water = no life.).

8. I. Ch 12, Sec 1 - Is Earth Unique?
The Right Location
3) Our medium-sized sun has a nice long 10 billion year life span. If the Sun was a giant star, it would burn hotter and “burn out” in just a few 100 million years. There would not have been enough time for any significant evolution to occur.

9. I. Ch 12, Sec 1 - Is Earth Unique?
The Right Time
1) There has been enough time for the atmosphere to develop. The early atmosphere contained methane, ammonia, water vapor and carbon dioxide. There was no free oxygen (O2).

10. I. Ch 12, Sec 1 - Is Earth Unique?
The Right Time
2) Photosynthetic bacteria released O2 into the atmosphere. The appearance of O2 in the atmosphere made possible the evolution of higher organisms.

11. I. Ch 12, Sec 1 - Is Earth Unique?
The Right Time
3) 65 mya – Earth was struck be a 6 mile diameter asteroid, causing a mass extinction which killed off 75 % of all plant and animal life.

12. I. Ch 12, Sec 1 - Is Earth Unique?
The Right Time
4) The extinction of the dinosaurs made possible the rise and diversification of mammals.

13. Proto-Earth:

14. II. Ch 12, Sec 2 – Birth of a Planet
B. Earth’s Early Evolution. The first ¾ of a billion years of Earth’s history (from 4.6 – 3.8 bya) is called the Hadean Eon:

15. II. Ch 12, Sec 2 – Birth of a Planet
Proto-Earth was a chunky dust ball which weighed much less than its present mass, but was much bigger across.

16. II. Ch 12, Sec 2 – Birth of a Planet
B. The sun was just warming up then, so proto-Earth was very chilly: - 347o F
( 347o below zero F )
( 40o above absolute zero )

17. II. Ch 12, Sec 2 – Birth of a Planet
C. Proto-Earth was heated up very quickly by:
1) Gravitational Compression
2) Intense Radioactivity (from minerals and elements inside the earth

18. II. Ch 12, Sec 2 – Birth of a Planet
C. Proto-Earth was heated up very quickly by:
3) Millions of Meteorite Impacts which terrorized the early solar system until about 3.9 billion years ago (bya)

19. Meteorite Bombardment

20. Proto-Earth

21. II. Ch 12, Sec 2 – Birth of a Planet
4.6 bya – 3.8 bya
D. The intense meteorite bombardment and radioactive decay caused Earth’s crust to heat up and completely melt, resulting in a magma ocean (about 4.5 bya).

22. II. Ch 12, Sec 2 – Birth of a Planet
bya
E. During this molten phase, the heavier metals Iron and Nickel sank to form an Iron-rich core and a thick mantle of iron-rich silicate rocks…

23. II. Ch 12, Sec 2 – Birth of a Planet
E. …while the lower density (“lighter”) silicate rocks rose closer to the surface to form a thin primitive crust. This major sorting-out event is known as the Iron Catastrophe.

25. II. Ch 12, Sec 2 – Birth of a Planet
F. Although it was hotter, the inner core solidified first, because the tremendously high pressures at the center allowed iron to crystallize and harden at 5000o C. That is hotter than the surface of the Sun!
Crystalline Iron Meteorite
Similar to Crystalline Iron Found in Earth’s Core

26. II. Ch 12, Sec 2 – Birth of a Planet
G. 50 million years later, the outer 500 miles of the earth cooled and hardened into the crust and upper mantle.
Earth’s layering was completed 4.4 billion years ago (b.y.a.)

27. 4 Layers of the Earth
Crust
Mantle
Liquid Outer Core
Solid Inner Core

28. II. Ch 22, Sec 2 – Mars-Sized Planetesimal Impacts Earth…
4.5 bya

29. II. Ch 22, Sec 2 –…to form the Moon

30. II. Ch 22, Sec 2 –…to form the Moon
4.45 bya

31. 3 Hypotheses on the Formation of the Solar System
Remember:
A 2 million mph solar wind and deadly U-V radiation stripped away the gas layers of the 4 inner planets (they’re now rocky).

32. III. Ch 12, Sec 3 – Origin of the Atmosphere and Oceans
A. Earth’s original atmosphere was stripped away by an intense solar wind, so Earth has had to “grow” a new one!
B. Earth’s early atmosphere contained Hydrogen (H), Helium (He), Methane (CH4), Ammonia, (NH3), Carbon dioxide (CO2) and steam / water vapor (H2O).

33. Early oceans

34. III. Ch 12, Sec 3 – Origin of the Atmosphere and Oceans
C. Earth acquired its water from two main sources:
1) Earth was bombarded by icy planetesimals and comets from beyond Mars that vaporized when they struck Earth. Earth’s gravity kept the water from escaping.

35. III. Ch 12, Sec 3 – Origin of the Atmosphere and Oceans
C. Earth acquired its water from two main sources:
2) Worldwide volcanic eruptions released lava but also caused a lot of volcanic outgassing, releasing Carbon dioxide, Nitrogen and Sulfur oxides and a large amount of steam (boiling hot water vapor) into the atmosphere.

36. III. Ch 12, Sec 3 – Origin of the Atmosphere and Oceans
Hot gases & Steam
Volcano

37. III. Ch 12, Sec 3 – Volcanic Outgassing
Hot gases & Steam
Volcano

38. III. Ch 12, Sec 3 – Origin of the Atmosphere and Oceans
D. The early atmosphere was 50 % water (H2O vapor) with a lot of CO2 & NO2:
1) The C from CO2 combined with H to make methane (CH4).
2) The N from NO2 combined with H to form ammonia (NH3).

39. III. Ch 12, Sec 3 – Origin of the Atmosphere and Oceans
D. The early atmosphere was 50 % water (H2O vapor) with a lot of CO2 & NO2:
3) Loose H and He atoms escaped into space because Earth’s gravity was too weak to hold on to these very light gases.

40. III. Ch 12, Sec 3 – Origin of the Atmosphere and Oceans
E. The steam caused thunderstorms which raged for centuries.

41. III. Ch 12, Sec 3 – Origin of the Atmosphere and Oceans
F. Earth’s early ocean was a relatively fresh-water sea.
It took many more years of acid rain to wash enough Na and Cl out of the rocks and down the rivers to the oceans to make salt water.

42. III. Ch 12, Sec 3 – Origin of the Atmosphere and Oceans
G. Most importantly, there was no free oxygen (O2) in Earth’s atmosphere until 2.0 b.y.a., so early life forms were limited to those that didn’t need oxygen (they were anaerobic).

43. III. Ch 12, Sec 3 – Origin of the Atmosphere and Oceans
H. Oxygen first appeared during the Great Oxygenation Event 2.4 by ago due to:
1) Photosynthetic bacteria
esp. the blue green kind
followed later by green algae and plants

44. Bacterial Stromatolites – earliest photosynthetic bacteria
Modern Stromatolites – Shark’s Bay, Australia
Fossil Stromatolites –
Earth’s oldest fossils

45. III. Ch 12, Sec 3 – Origin of the Atmosphere and Oceans
H. Oxygen first appeared during the Great Oxygenation Event 2.4 by ago due to:
2) Splitting of water molecules in
the sky (electrolysis) by:
lightning and
U-V radiation

46. Splitting of Water Molecules by Lightning and UV rays

47. III. Ch 12, Sec 3 – Origin of the Atmosphere and Oceans
I. With the addition of oxygen (O2), and the resulting ozone layer (O3), life on Earth really took off!