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Earth
Chapter 7
Basic Properties
• Terrestrial planet (the original!)
• Composition
– rocky (heavy elements: oxygen, silicon, iron)
– very different from sun and Jovian planets
• Orbit
– nearly circular
• Climate
– Not too hot, not too cold: JUST RIGHT!
• only planet with liquid water
• water necessary for life
Earth: The Water Planet
Earth’s Interior
Probing Earth’s Interior
• Earthquakes
– Seismic waves
– Penetrate interior
– Path depends
on material
properties
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Earth’s Interior
• Temperature increases
toward center
– Rock melts
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• Differentiation
– Interior is molten
– Heavy elements sink; light elements float
• Core is molten iron (density 8 gm/cm3)
• Mantle is partially melted (density 5 gm/cm3)
• Crust is solid (density 3 gm/cm3)
• Crust Floats on Mantle
Earth’s Crust
Plate Tectonics
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70 million yrs ago
200 million yrs ago
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500 million yrs ago
700 million yrs ago
Plate Tectonics
•Volcanic and earthquake activity occurs on plate boundaries
Mantle Convection
•
•
•
•
Heat escapes core; heats mantle
Hot mantle rises
Convection
Cold mantle sinks
Convection flow carries crust sideways
Subduction
Rift Zone
Subduction
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Rift and Subduction Zones
Slip Fault
Rift Zone
Subduction Zone
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Rift Zone
• Occurs when crust is split apart
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Subduction
• Occurs when plates pushed together
Pacific Northwest
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Mt. St. Helens Eruption
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Uplift: Building
Mountain Ranges
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Slip Fault
• Occurs where plates slip sideways
San Andreas Fault
Hawaiian Island Chain
• Line of successive volcanoes; middle of plate
• Produced when plate travels over “hot spot”
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Repaving the Earth
• Ocean floor renewed in few 100 million yrs
• Continents last longer
– Surface features erased by erosion
(water and wind)
• Evidence of craters erased in time
– Oldest rocks on earth about 3.8 billion yrs old
• Radioactive dating
Volcanoes are usually found in places where:
A. the low pressure of the atmosphere pulls
the lava/magma to the surface.
B. earthquakes occur from oceanic plates
colliding with continental plates.
C. deep-rooted mountains have cracked
Earth’s crust.
D. Earth’s rotation has caused weak spots in
its crust.
The change in position of the continents over
time is primarily caused by
A.
B.
C.
D.
continental plates floating on the ocean.
mantle material circulating inside Earth.
Earth’s slow shrinking as it cools.
global wind patterns and sustained ocean
currents.
Earth’s Atmosphere
• Composition
–
–
–
–
Mostly nitrogen, N2 (78%)
Some oxygen, O2 (21%)
A little water, H2O
Teeny, tiny bit of carbon dioxide CO2
• Atmospheric Pressure
– 14.7 pounds per square inch (1 bar)
– Produced by weight of atmosphere above us
Atmospheric Protection
• Ozone, O3
– Ozone absorbs ultraviolet light
– Protects us from sunburn
– Ozone destroyed by chlorine
• NOTE: Ozone destruction NOT same
problem as global warming!
Ozone and CFCs
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2000 Ozone hole
Over Antarctica
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Change in CFC-11
Last 20+ years
Chemical Evolution of Atmosphere
• Original Atmosphere
– Mostly carbon dioxide, CO2
• Current Atmosphere
– Mostly nitrogen, N2
– Oxygen disappears (a few 1000 yrs) if not replenished
(oxygen produced by plants)
• Where did CO2 go?
– Bound in rocks
(like limestone, calcium carbonate, CaCO3)
• Where did nitrogen and water come from?
– Volcanic activity releases N2 and water, H20
– Comets falling on Earth release water
Greenhouse Effect
• Sunlight absorbed by ground
• Heat emitted using infrared light
• Infrared light trapped by gasses in
Earth’s atmosphere
– Greenhouse gasses:
• Carbon Dioxide (CO2)
• Water (H2O)
• Heat cannot escape
• Earth’s surface gets hotter
– about 23 degrees C (40 degrees F)
Global Warming
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Atmospheric Protection
• Meteors (“shooting stars”)
– Small rocks melt/burn up before hitting surface
– Larger objects can get through
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1833 Leonid Storm
1998 Leonids
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1997 Leonids
Seen by MSX
Meteor
Showers
Causes of Meteor Showers
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Peekskill
Meteorite
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1992
Perils from Space
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Effects of Impacts
• Where are the craters on Earth?
– erased by geologic activity
• volcanoes, earthquakes, plate tectonics
– erased by erosion
• weather, rain, wind
• Evidence for impacts?
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– some craters still exist (Meteor Crater, AZ)
– geologic evidence of old craters
– occasional impacts today
• Effects of impacts?
– global climate changes
• mass extinctions? (dinosaurs)
– water in oceans?
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