1. Earth Astronomy 311 Professor Lee Carkner Lecture 12

2. Terra -- The Earth Goddess  Greeks and Romans personified the Earth as a mother goddess

3. Earth Facts  Size: 12700 km diameter   Orbit: 1 AU (1.5 X 10 8 km)  Description: wet, temperate, inhabited

4. Earth’s Celestial Motions  Earth is tilted on its axis by 23 1/2 degrees   Earth has large satellite, The Moon    May stabilize tilt of axis

5. Earth’s Atmosphere  Composition:    small amounts of water vapor, CO 2 other gasses  Very different from other atmospheres  

6. Early Atmosphere  Where did the original atmosphere come from?    Early composition:  Carbon dioxide (CO 2 )  Water (H 2 O)  Methane (CH 4 )  Ammonia (NH 3 )

7. Formation of Atmosphere  Start with CO 2, H 2 O, CH 4, NH 3   C, H, O form H 2 O, CO 2  CO 2 dissolves in H 2 O, H 2 O rains out to form oceans, N 2 left behind   Final atmosphere -- O 2 and N 2

8. Earth’s Atmosphere

9. Temperature  Temperature and composition of Earth’s atmosphere is regulated by the carbonate-silicate cycle    Surface temperature stays near the point where water is mostly liquid

10. Climate  The atmosphere circulates due to convection (hot thing rise, cool things sink)  Two basic sources of convection    The Earth’s rotation breaks the atmosphere up into convection cells that keep the air circulating, producing global weather patterns

11. The Earth’s Surface  What shapes the Earth’s surface?    Also, volcanoes and cratering  Unlike other planets the Earth does not have many craters  Craters on Earth are largely obliterated by erosion

12. Plate Tectonics  The two top layers of the Earth are the crust and the mantle    Crust is broken up into plates that float on the upper mantle  Plates move around and crash into each other forming trenches and mountains 

13. How Plate Tectonics Work

14. Plate Boundaries

15. Water  The Earth has more liquid water on its surface than any other planet  Water is present on Earth in all three phases (ice, liquid water, vapor) and continuously cycles between them    

16. Water on the Earth

17. Effects of Surface Alteration  Plate tectonics and erosion alter the Earth’s surface      Earth’s surface is constantly changing

18. Plate Collision -- The Himalayas

19. The Grand Canyon

20. Meteor Crater

21. The Earth’s Interior  The crust and atmosphere are very thin compared the rest of the planet (like the skin of an orange)   We learn about them by studying the seismic waves from earthquakes

22. Seismic Waves  Types of waves:  P waves: pressure or compression wave   S waves: shear waves   The different densities of the inner earth refract the waves   When an earthquake occurs we can measure the strength of S and P waves all over the Earth

23. Earthquake Studies of the Earth’s Interior

24. Seismic Waves and the Earth’s Interior  No S waves detected on opposite side of Earth    There is a shadow zone where no P or S waves are detected   Very faint P waves detected in shadow zone  Refracted by solid inner core

25. Structure of the Earth  Crust:  surface to 35 km   Mantle  35-2900 km   Outer core  2900-5100 km   Inner core  5100-6400 km   Density increases toward the center

26. Structure of the Earth

27. Earth’s Magnetic Field  Rotation and the motions of the liquid iron core produce a magnetic field via the dynamo effect   This magnetic field helps shield the Earth from the solar wind

28. The Earth’s Magnetosphere

29. The Habitable Zone  In order to support life a planet must be in the habitable zone   Width of zone determined by the effectiveness of the carbonate-silicate cycle  Inner Edge --  Outer Edge --  For our solar system habitable zone width is about 0.95-1.37 AU

30. Hypothetical Habitable Zone Too hot, water is destroyed can’t remove CO 2 Too cold, try to warm up with more CO 2 but CO 2 forms clouds and blocks sunlight Just right, temperature kept stable at ~273 K (water is liquid)

31. Why is the Earth Habitable?  It has the right temperature for liquid water (~273 K) because:    Has both water and plate tectonics for carbonate-silicate cycle

32. Summary  Earth is unique for at least two reasons  Large amounts of liquid water   Large amounts of free oxygen   Earth has liquid water and life because it is in the habitable zone

33. Summary: Atmosphere  Earth’s initial atmosphere composed of CHON      Mild temperature maintained by carbonate-silicate cycle

34. Summary: Surface  Solid iron inner core, liquid iron outer core, solid mantle and crust   Plate tectonics and erosion constantly alter surface