Earth : Plate Tectonics and Magnetic Field

1. Earth : Plate Tectonics and Magnetic Field Lecture 17

2. OASIS in the Solar System

3. Dynamic Earth

4. Energy Sources of Dynamic Earth Solar energy, tidal forces, and internal heat (trapped heat + radio active material)

5. Formation & evolution of Earth

6. Differentiation

7. 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!

8. Internal Structure of Earth

9. Internal Energy Source  convection

10. Plate Tectonics http://www.youtube.com/watch?v=ZLJLFYXp-0Q

11. Continental Drift Fitting the Continents Together Africa, Europe, Greenland, North America, and South America fit together remarkably well. 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

12. 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.

13. Boundaries of Plates • 8 major plates + dozens of smaller plates • Major Earthquakes happened at plate boundaries

14. At plate boundaries…

15. Hot Spots Sometimes, localized plume of mantle material get uplifted… Hawaiian islands Yellow Stone Park

16. On-going… • In ~100 Myrs, California will slide northward to Alaska, the Mediterranean Sea will become mountains, Australia will merge with Antarctica

17. Plate Tectonics CO2Cycle 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

18. Cause of Magnetic Field • Requirements for a magnetic field • Electrically conducting fluid • Convection • Rotation of the planet Electromagnet

19. 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

20. 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!

21. Auroras : northern & southern lights Aurora Borealis : Aurora Australis :

22. Aurora in Georgia! Oct. 29, 2003. Dahlonega, GA Triggered by a coronal mass ejection…

23. On other Planets, too! Jupiter seen in X-ray (Chandra satellite) Saturn seen by Cassini (optical)

24. In summary… Important Concepts Important Terms Asthenosphere Convection Plate tectonics Differentiation • Energy sources of Earth • Internal structure of Earth • Plate Tectonics • plate boundaries • Magnetic field • cause • as a shield • Chapter/sections covered in this lecture : sections 9-1 through 9-4