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Lecture #3

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Lecture #3

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  1. Lecture #3 Earth structure and plate tectonics 21 August 2007

  2. Lecture schedule LectureDateTime 1. Introduction to scientific writing 8/20 9:00-10:20 2. How to write a scientific paper in English 8/20 15:00-16:20 3. Earth structure and plate tectonics 8/21 9:00-11:00 4. Circulation of the atmosphere 8/21 13:00-15:00 5. Water and ocean structure 8/22 10:00-11:00 6. Continental margins and ocean basins 8/22 13:00-15:00 7. Sediment 8/23 10:00-12:00 8. Marine resources 8/23 13:00-14:00 9. Circulation of the ocean 8/24 11:00-12:30

  3. Earth is an Ocean World 71% of Earth’s surface is covered by water >97% of water at Earth’s surface is in oceans www.harmsy.freeuk.com/earth.html

  4. ArcticOcean Atlantic Ocean Pacific Ocean Indian Ocean All oceans and seas together = the “world ocean” http://www.uwsp.edu/geO/faculty/ritter/geog101/textbook/images/maps/oceans_CIA_base.jpg

  5. A few statistics: Average land elevation = 840 m Average ocean depth = 3,800 m Average ocean temperature = 3.9oC About 50% of Earth’s population lives <240 km from the ocean • In Japan, 96% of the population lives<100 km from the ocean

  6. Northern Hemisphere • 61% ocean Equator Southern Hemisphere • 81% ocean http://www.uwsp.edu/geO/faculty/ritter/geog101/textbook/images/maps/oceans_CIA_base.jpg • BUT, on a planetary scale, the ocean is small • 0.13% of Earth’s volume • more water within Earth’s interior than in its ocean and atmosphere

  7. Origin of the ocean To understand the ocean, we need to know how itformed and evolved. The formation of the ocean is linked to the formation of Earth and of the solar system.

  8. Earth Was Formed of Material Made in Stars • The universe began with the big bang • about 14 billion years ago • atoms began to form after about 1 million years • mostly hydrogen cooling http://outreach.web.cern.ch/outreach/public/cern/PicturePacks/BigBang/BigBang.JPG

  9. Starsand planets are contained in galaxies A galaxy is a huge, rotating aggregation of stars, dust, gases and other debris. There are perhaps 100 billion galaxies in the universe. Our galaxy is named the Milky Way. http://www.atlasoftheuniverse.com/milkyway.jpg

  10. Milky Way • stars are arrayed in spiral arms • contains 200-400 billion stars • our sun is a typical star Spiral arms http://www.atlasoftheuniverse.com/milkyway.jpg

  11. Solar system http://www.astroarts.co.jp/news/2006/08/16planet_definition/index-j.shtml How do stars and planets form?

  12. Condensation theory spinning nebulae (a large cloud of gas and dust) Material concentrated near its center became the protosun • much of the outer material eventually became the planets • formed by accretion http://physics.uoregon.edu/~jimbrau/BrauImNew/Chap06/FG06_20.jpg

  13. Formation of Earth The young Earth was probably homogenous throughout • Density stratification is layering by density • the heaviest material forms deeper layers, and the lighter material forms layers near the surface. Earth began to cool. • The first surface formed about 4.6 billion years ago. • so we say Earth is 4.6 billion years old

  14. Earth’s Interior is Layered Inside How can we study Earth’s interior? Dig a hole? http://www.nasa.gov/images/content/103949main_earth10.jpg

  15. Kola Superdeep Borehole (KSDB) • a scientific drilling project in the USSR to drill into the Earth's crust • goal = 15 km • began digging in 1970 • in 1992, reached a final depth of 12 km • 245oC! <1/500 of Earth’s radius

  16. Ocean drilling JOIDES Resolution (1985 - ) • scientific drilling ship • penetrated 2 km below 2.5 km of seawater http://www-odp.tamu.edu/images/bluejr.jpg Chikyu (2002- ) 210 m http://en.wikipedia.org/wiki/Image:DVChikyu.jpg

  17. Chikyu Hakken (地球発見) • Japanese for "Earth Discovery“ • a mission primarily led by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) • AIM: be the first to drill seven kilometers beneath the seabed and into Earth’s mantle http://www.jamstec.go.jp/chikyu/eng/index.html

  18. Chikyu Hakken (地球発見) • Japanese for "Earth Discovery“ • a mission primarily led by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) • AIM: be the first to drill seven kilometers beneath the seabed and into Earth’s mantle No one has yet sampled below Earth’s outermost layer, the Crust. So how do we know Earth is layered? http://www.jamstec.go.jp/chikyu/eng/index.html

  19. Chikyu Hakken (地球発見) • Japanese for "Earth Discovery“ • a mission primarily led by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) • AIM: be the first to drill seven kilometers beneath the seabed and into Earth’s mantle No one has yet sampled below Earth’s outermost layer, the Crust. So how do we know Earth is layered? Earthquakes http://www.jamstec.go.jp/chikyu/eng/index.html

  20. Earthquakes generate seismic waves. Seismic waves travel through Earth and along its surface. • Seismic waves form in two types: • surface waves • sometimes seen as an wavelike motion in the ground • cause most of the property damage in an earthquake • 2) body waves (P and S waves) • useful for analyzing Earth’s interior structure http://ja.wikipedia.org/wiki/%E7%94%BB%E5%83%8F:Pswaves.jpg

  21. Body waves 1) P (primary) wave • a compressional wave • similar to a sound wave • pass through liquids and solids http://www.met.gov.pk/Subpage4/waves_files/pwave_web.jpg 2) S (secondary) wave • a shear wave • like a rope shaken side to side • pass through solids only • about 1/2 the speed of P waves http://www.geo.uib.no/jordskjelv/img/s-wave.jpg

  22. seismograph

  23. P waves are faster than S waves About 3.5 km/sec About 6 km/sec

  24. Sumatra-Andaman earthquake (26 December 2004) http://zog.typepad.com/malaysia/epicenter.jpg How do we locate theepicenter of an earthquake?

  25. http://www.theimage.com/geology/notes15/index.html http://ja.wikibooks.org/wiki/%E9%98%B2%E7%81%BD_%E5%9C%B0%E9%9C%87 http://www.calstatela.edu/faculty/acolvil/earthquakes.html

  26. If the Earth were homogenous, the paths of seismic waves would be straight lines • Richard Oldham • British geologist http://cires.colorado.edu/~bilham/oldham.gif

  27. If the Earth were homogenous, the paths of seismic waves would be straight lines • Richard Oldham • British geologist http://cires.colorado.edu/~bilham/oldham.gif Found that seismic waves arrived earlier than expected at seismographs far from the quake waves traveled faster as they went into Earth

  28. Earthquake wave shadow zones confirmed the presence of Earth’s core.

  29. refraction

  30. Data from an earthquake confirmed the model of Earth layering. Anchorage, Alaska 27 March 1964 9.2 on Richter scale • P and S waves were very large and easily detected at great distances • helped confirm the models of Earth layering. http://www.greatdreams.com/alaska/alaska-collapse-1964.jpg

  31. Question Time! 1. What are the two kinds of seismic waves?

  32. Earth’s Inner Structure was Gradually Revealed. • Researchers have not collected samples from below the outermost layer of Earth. • but they have indirect evidenceabout • chemical composition • density • temperature • thickness

  33. Earth’s layers can be classified based on composition. • Crust • 1% of Earth’s volume • oceanic crust • mostly basalt • continental crust • mostly granite • Mantle • 83% of Earth’s volume • mainly silicon and oxygen • Core • 16% of Earth’s volume • mainly iron (90%) and nickel http://www.llnl.gov/str/JulAug04/gifs/Fried1.jpg

  34. Earth’s layers can also be classified by physical properties. • Lithosphere • cool, rigid • Athenosphere • hot, partially melted Lower mantle • Core • outer core • liquid • inner core • solid • 6,600oC!

  35. Isostatic equilibrium supports continents above sea level The lithosphere “floats” on the asthenosphere buoyancy Iceberg Isostatic equilibrium

  36. What happens when a mountain erodes? • Isotatic uplift • now occurring in Canada and United States • caused by melting of ice sheets • one cause of earthquakes

  37. How do mountains form? Himalayas http://upload.wikimedia.org/wikipedia/commons/thumb/7/79/Himalayas.jpg/350px-Himalayas.jpg

  38. How do mountains form? Himalayas http://upload.wikimedia.org/wikipedia/commons/thumb/7/79/Himalayas.jpg/350px-Himalayas.jpg In 1800s, geologists thought that the Earth shrunk as it cooled http://www.grape.sk/grape_2006.jpg http://en.wikipedia.org/wiki/Image:Single_raisin.jpg

  39. Earth’s interior is heated by the decay of radioactive elements • Some elements are unstable • give off heat when their nuclei beak apart Some of this heat moves to the surface by conduction Some also rises by convection This heat: - builds mountains and volcanoes - causes earthquakes - moves continents

  40. The age of Earth was controversial and not easily determined. Earth is about 4.6 billion years old. But, in late 1700s, most European scientists thought the year was only 6,000 years old!

  41. The age of Earth was controversial and not easily determined. Earth is about 4.6 billion years old. But, in late 1700s, most European scientists thought the year was only 6,000 years old!

  42. James Hutton (1726-1797) • Scottish geologist • the father of modern geology • he argued that Earth is much older than 6,000 years

  43. In mid-late 1700s, a strong debate between: Catastrophism vs. Uniformitarianism Gradually evidencebegan to support uniformitarianism

  44. The fit between the edges of continents suggested that they might have drifted. jigsaw-puzzle fit

  45. Alfred Wegener (1880-1930) • German meteorologist and polar explorer • in 1912, proposed the theory of continental drift • Pangaea • landmass • Panthalassa • surrounding ocean (http://physics.fortlewis.edu/Astronomy/astronomy%20today/CHAISSON/AT307/IMAGES/AT07FG21.JPG)

  46. Evidence from: fossils (http://hyperphysics.phy-astr.gsu.edu/hbase/geophys/platevid.html) glacial deposits http://www.indiana.edu/~g103/G103/week11.htm

  47. Evidence from: fossils (http://hyperphysics.phy-astr.gsu.edu/hbase/geophys/platevid.html) glacial deposits But how? http://www.indiana.edu/~g103/G103/week11.htm

  48. The idea of continental drift evolved as evidence accumulated 和達清夫 Kiyoo Wadachi (1902-1995) http://en.wikipedia.org/wiki/Pacific_Ring_of_Fire http://www.japan-acad.go.jp/image/common/wadati.jpg • speculated that this could be associated with continental drift

  49. More evidence: • Radiometric dating • oldest rocks on ocean floor <200 million years old • Echo sounders • showed a large mountain range in the middle of the Atlantic Mid-Atlantic Ridge

  50. A synthesis of continental drift and seafloor spreading produced the theory of plate tectonics. Harry Hess (1906-1969) Robert Dietz (1914-1995) http://scilib.ucsd.edu/sio/archives/photos/dietz.jpg • proposed the theory of seafloor spreading