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Earth : Plate Tectonics and Magnetic Field
Lecture 17
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OASIS in the Solar System
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Dynamic Earth
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Energy Sources of Dynamic Earth
Solar energy, tidal forces, and internal heat (trapped heat + radio active material)
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Formation & evolution of Earth
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Differentiation
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How do we know the internal structure of the Earth?
Based on the propagation pattern of seismic waves, scientists deduced that there should be 3 layers inside of the Earth!
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Internal Structure of Earth
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Internal Energy Source convection
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Plate Tectonicshttp://www.youtube.com/watch?v=ZLJLFYXp-0Q
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Continental Drift
Continental Drift was proposed by meteorologist and geologist Alfred Wegener in 1912
The idea was inspired by the puzzle-like fit of South America and Africa, indicating these two continents were part of a single “supercontinent” about 200 million years ago
Fitting the Continents Together Africa, Europe, Greenland, North America, and
South America fit together remarkably well.
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Plate Tectonics
Internal heat makes hot material expand and rise while cooler material on top contracts and falls
Plate tectonics produces and recycles seafloor crust (that is why the seafloor crust is usually less than 200 million years old). At ocean trenches, the seafloor crust pushes under the less dense continental crust, returning the seafloor crust to the mantle and may cause volcanic eruptions.
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8 major plates + dozens of smaller platesMajor Earthquakes happened at plate boundaries
Boundaries of Plates
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At plate boundaries…
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Hot SpotsSometimes, localized plume of mantle material get uplifted…
Hawaiian islandsYellow Stone Park
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On-going…
In ~100 Myrs, California will slide northward to Alaska, the Mediterranean Sea will become mountains, Australia will merge with Antarctica
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Plate Tectonics CO2 Cycle
On Earth, CO2 content in the air is regulated by the Carbon Dioxide Cycle to avoid runaway Greenhouse effect
Carbonate rocks : limestone, calcite, dolomite, chalk, …
Plate tectonics is the key element of long-term stability of the Earth!
CO2 in the Earth : atmosphere 1, ocean 60, rocks 170,000
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Cause of Magnetic Field
Electromagnet
Requirements for a magnetic field• Electrically conducting fluid• Convection• Rotation of the planet
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Magnetic field interacts with Solar winds!High velocity electrified gas (plasma) blows into the Earth at speed of ~250 miles/second!http://www.gsfc.nasa.gov/gsfc/spacesci/pictures/20020509imagessu/magneticfield_mpeg.mpg
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Magnetic Field
Charged particles from solar flares interact with earth’s magnetic field and atoms and molecules in Earth’s atmosphere and produce aurora.Without the magnetic field, our atmosphere would have been stripped away by the strong solar wind!
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Aurora Borealis : Aurora Australis :
Auroras : northern & southern lights
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Aurora in Georgia!Oct. 29, 2003. Dahlonega, GA
Triggered by a coronal mass ejection…
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On other Planets, too!
Jupiter seen in X-ray (Chandra satellite)Saturn seen by Cassini (optical)
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In summary…
Important ConceptsEnergy sources of EarthInternal structure of EarthPlate Tectonics• plate boundaries
Magnetic field • cause• as a shield
Important TermsAsthenosphereConvectionPlate tectonicsDifferentiation
Chapter/sections covered in this lecture : sections 9-1 through 9-4