Transcript Document

Planetary Geology
Planets Rock!
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Goals
• What determines why planets look the way they
do.
• What are the 4 main process that affect a planet’s
surface.
• How does planetary interior affect planetary
atmospheres?
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Why are planets different?
• Different planets look different.
• What determines this?
• To understand the outside, you must
understand the insides.
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Concept Test
•
The cores of the terrestrial worlds are made
mostly of metal because ______.
a. the terrestrial worlds as a whole are made mostly of
metal.
b. the core contained lots of radioactive elements that
decayed into metals.
c. over billions of years, convection gradually brought
dense metals downward to the core.
d. metals sunk to the centers a long time ago when the
interiors were molten throughout.
e. None of the above.
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Internal Heat
• Why is heat the driver of
geological processes?
• What is heat?
• Think of temperature on an
atomic scale.
• Where do you expect
change?
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• Planets form out of primordial
cloud of gas and dust.
• Atoms to dust to grains to rocks
to asteroids to planetesimals to
planets.
Accretion
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Differentiation
• Accreted material is all mixed.
• Friction generates heat.
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Lithosphere – Radius at which rock is
too cool to flow by convection.
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Concept Test
•
Given this description of planetary interiors, we
expect:
a. Smaller planets should cool off faster than bigger
ones.
b. Larger planets should have thinner lithospheres than
smaller planets.
c. There should be fewer signs of geological activity on
the surfaces of smaller planets compared to larger
ones.
d. All of the above.
e. None of the above.
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How do we know?
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How do we know what is really going on inside
planets?
1. Look for signs of surface activity. Has anything
changed recently?
2. Look for magnetic fields around planet.
1. Fluid core
2. Convection of fluid
3. Rapid rotation
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Comparative Planetology
• 4 main surface altering processes
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Cratering (exogenic)
Volcanism (endogenic)
Tectonics (endogenic)
Erosion (endogenic)
• In order for endogenic processes
to occur, energy must be available.
• Small planets (and moons, and asteroids)
generally have little internal heat, and, therefore,
little endogenic activity.
• Exogenic processes affect everything.
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Volcanoes
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Volcanoes
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Tectonics
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e 9.13B
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Plate
Tectonics
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Erosion
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Alluvial Fan
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Craters
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New Surface vs. Old
• Impacts happen over time.
• Can date a surface by the number of craters on its
surface. Date since last geologic activity.
• Pot holes on road:
– Many holes = old road.
– Few holes = new road
• Resurfacing = energy
– One or more endogenic
processes.
• Another clue to insides.
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Why is Earth so Different?
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Why do we have oceans of water?
Why doe we have an atmosphere with:
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so little carbon dioxide?
so much O2 and N2?
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Atmosphere Origins
• Outgassing
• Volcanoes.
• CO2 and H2O main
gases.
• Mt. St. Helens
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Concept Test
•
For which terrestrial planets is the main
atmospheric gas one of the two main gases
produced by outgassing?
a.
b.
c.
d.
e.
Only Moon & Mercury
All five planets
Only Venus, Earth and Mars
Only Earth
Only Venus and Mars
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The Terrestrial Planets
World
Atmos.
Compsn.
Surface
Pressure
Ave Surface
Temp.
Winds,
Weather
Clouds,
Hazes
Mercury
He, Na, O
10-14 bar
Day: 800F
Night: -280F
none
none
Venus
96% CO2
3.5% N2
90 bars
880F
Slow winds,
acid rain
Sulfuric acid
clouds
Earth
77% N2
21% O2
H2O
1 bar
60F
Winds,
hurricanes,
rain, snow
H2O clouds,
pollution
Moon
He, Na, Ar
10-14 bar
Day:260F
Night: -280F
none
none
Mars
95% CO2
2.7% N2
0.007bar
-60F
Winds, dust
storm
H2O and
CO2 clouds,
dust
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Goldilocks Planet
• Delicate balance: Earth
is just right.
– No oceans without
greenhouse gasses.
– Without oceans too many
greenhouse gasses.
– Without oceans no life.
– Without life, no ozone.
– No ozone, no life.
• How does Earth
maintain this balance?
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Carbon Cycle
Tectonics are crucial!
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Nature’s Thermostat
• Carbon Cycle has negative feedback.
• Increasing temperatures lead to feedback that
decreases temperatures, etc.
• Positive and negative feedbacks have nothing to
do with desirability of outcome.
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Too Cool
Less Rain
Less CO2
dissolves in
oceans.
More CO2
builds up in
atmosphere
Increased
greenhouse
Heats Up.
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Too Warm
More Rain
More CO2
dissolves in
oceans.
Less CO2
builds up in
atmosphere
Decreased
greenhouse
Cool Down.
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Cycles
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Human Input
• Affecting CO2
cycle.
• Moving C from
ground to air at
increased rate.
• No increase in rate
of C from air to
ground.
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Mars Today
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Positive Feedback
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Fossil Fuels – Increase CO2 to atmosphere.
Deforestation – decrease CO2 from atmosphere
Increase CO2 – Increase greenhouse effect
Increase temp – Melting glaciers, ice sheets, polar
caps
• Less ice – lower planetary albedo
• Lower albedo – Earth absorbs more light
• More absorption – Increasing surface
temperatures.
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Homework #6
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Due Monday January 30:
Read Bennett Chapter 6.
Do: Chapter 6 Quiz
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