1. Earth
Astronomy 311
Professor Lee Carkner
Lecture 12

2. The high temperature of Venus is due to the lack of what compound?
Carbon Dioxide
Water
Ammonia
Sulfur Dioxide
Oxygen

3. Which of the following is not evidence for volcanism on Venus?
Shield volcanoes
Lava domes
A smoothed surface
Smoke rising from active volcanoes
Sulfur in atmosphere

4. Terra -- The Earth Goddess
Greeks and Romans personified the Earth as a mother goddess
We use the old English names for the Earth, Sun and Moon, rather than the Latin ones

5. Earth Facts Size: 12700 km diameter Orbit: 1 AU (1.5 X 108 km)
Description: wet, temperate, inhabited

6. Earth’s Atmosphere Composition: Very different from other atmospheres
Outer planets: mostly H2

7. Early Atmosphere Where did the original atmosphere come from?
Bombardment of icy planetesimals (comets)
Early composition:
Water (H2O)
Ammonia (NH3)

8. Formation of Atmosphere
Ultraviolet light breaks up some molecules (four key elements: C,H,O,N)
CO2 dissolves in H2O, H2O rains out to form oceans, N2 left behind
Life (plants) forms and produces O2
Final atmosphere -- O2 and N2

9. Earth’s Atmosphere

10. 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 -- where water is lost by UV dissociation
Outer Edge --
For our solar system habitable zone width is about AU

11. Hypothetical Habitable Zone
Too cold,
try to warm up
with more CO2
but CO2 forms
clouds and blocks
sunlight
Too hot,
water is destroyed
can’t remove CO2
Just right,
temperature
kept stable
at ~273 K
(water is liquid)
Hypothetical Habitable Zone

12. Why is the Earth Habitable?
Large enough to hold an atmosphere
Has both water and plate tectonics for carbonate-silicate cycle

13. Planet Temperature
Planets with no atmosphere have a temperature determined by radiation balance:
Emit radiation back into space
Temperatures are in Kelvin (K)
A temperature scale where 0 K is absolute zero
A summer day is about 300 K
To convert K to F:
TF = 1.8TK - 460

14. Radiative Power
Hot objects absorb and emit energy based on the Stefan-Boltzmann law
P = sAT4
Where:
s is a constant = 5.67 X 10-8 (W/(m2 K4))
for a sphere A = 4pr2
T is the temperature of the object (in K)

15. Energy Balance
If we compare the energy the Earth emits with the energy it gets from the Sun, we can find its temperature
TE = [RS/(2 DS)]½ TS
Where: TE
TS is the temperature of the Sun RS
DS is the distance from the Earth to the Sun

16. The Earth’s Surface What shapes the Earth’s surface? Water erosion
Plate tectonics raise up mountains, water erodes them down, the silt collects on the ocean floor and forms the rock to make the next mountains
Craters on Earth are largely obliterated by erosion

17. Plate Tectonics
The two top layers of the Earth are the crust and the mantle
Crust is hard and rigid
Plates move around and crash into each other forming trenches and mountains
Plates move a few inches a year

18. How Plate Tectonics Work

19. Plate Boundaries

20. Plate Collision -- The Himalayas

21. The Grand Canyon

22. 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

23. Seismic Waves Types of waves:
P waves: pressure or compression wave
example:
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

24. Earthquake Studies of the Earth’s Interior

25. Seismic Waves and the Earth’s Interior
No S waves detected on opposite side of Earth
Core must be liquid
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

26. Structure of the Earth

27. Structure of the Earth Crust: Mantle Outer core Inner core
surface to 35 km
Mantle km
composed of silicates and heavier material
Outer core km
Inner core km
composed of solid iron

28. Next Time
Read Chapter 8
Just the moon parts

29. Summary Earth is unique for at least two reasons
Large amounts of liquid water
constantly reshapes the surface
Large amounts of free oxygen
produced by life
Earth has liquid water and life because it is in the habitable zone

30. Summary: Atmosphere Earth’s initial atmosphere composed of CHON
H and O form water -- oceans
C and O form carbon dioxide -- rock
N stays in atmosphere
Plants produce oxygen
Mild temperature maintained by carbonate-silicate cycle

31. Summary: Surface
Solid iron inner core, liquid iron outer core, solid mantle and crust
Crust is broken up into plates which slide around on the upper mantle
Plate tectonics and erosion constantly alter surface