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The high temperature of Venus is due to the lack of what compound?
a) Carbon Dioxideb) Waterc) Ammoniad) Sulfur Dioxidee) Oxygen
Which of the following is not evidence for volcanism on Venus?
a) Shield volcanoesb) Lava domesc) A smoothed surfaced) Smoke rising from active
volcanoese) Sulfur in atmosphere
Terra -- The Earth Goddess
We use the old English names for the Earth, Sun and Moon, rather than the Latin ones
Earth’s Atmosphere
Composition: small amounts of water vapor, CO2 other
gasses Very different from other atmospheres
Inner planets: Outer planets:
Early Atmosphere Where did the original atmosphere come
from?
Bombardment of icy planetesimals (comets) Early composition:
Water (H2O) Ammonia (NH3)
Formation of Atmosphere
Start with CO2, H2O, CH4, NH3
C, H, O form H2O, CO2
Life (plants) forms and produces O2
Final atmosphere -- O2 and N2
Atmosphere and Temperature
Planets with no atmosphere have a temperature determined by radiation balance:
For a steady temperature, both rates must be equal
K stands for Kelvin, a temperature scale where 0 K is absolute zero The coldest anything can get
To convert K to F: TF = 1.8TK - 460
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
Hypothetical Habitable Zone
Too hot,water is destroyedcan’t remove CO2
Too cold,try to warm upwith more CO2
but CO2 formsclouds and blocks sunlight
Just right,temperaturekept stableat ~273 K(water is liquid)
Why is the Earth Habitable?
Large enough to hold an atmosphere Has both water and plate tectonics for
carbonate-silicate cycle
Climate
Two basic sources of convection Bottom of atmosphere is warmer than top
The Earth’s rotation breaks the atmosphere up into convection cells that keep the air circulating, producing global weather patterns
The Earth’s Surface
What shapes the Earth’s surface?
Resurfacing is cyclical and constant 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
Plate Tectonics
Upper mantle is soft and plastic Crust is hard and rigid
Plates move around and crash into each other forming trenches and mountains Plates move a few inches a year
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
The Earth’s Interior
We cannot view the inner layers directly (can’t drill deep enough)
We learn about them by studying the seismic waves from earthquakes
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
Seismic Waves and the Earth’s Interior
No S waves detected on opposite side of Earth Core must be liquid
Core mantle boundary refracts wave out of this zone
Refracted by solid inner core
Structure of the Earth
Crust: surface to 35 km
Mantle 35-2900 km composed of
silicates and heavier material
Outer core 2900-5100 km
Inner core 5100-6400 km
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
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