ESS8 lecture

ESS8 lecture - 9/27-San Andreas fault = Pacific and North...

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9/27 -San Andreas fault = Pacific and North American plates coming together -seismology = study of earthquakes, “seis” comes from Greek word for “tremor” -seismicity – seismic activity -seismologist – someone who studies earthquakes -quakes are non-uniform in space and time, but they have some patterns -distances huge (plates) and small (atoms on either side of a fault) -plates shifting = major cause of earthquakes -exponential notation = important 10/2 -North San Andreas = active, south = quieter -2 strands in Bay Area of San Andreas (including Hayward in Berkeley) -Quakes line up along fault -Earth = 6370 km radius -Oceans (70% of radius) have average depth of 4 km -continents have average elevation of 500 m a.s.l. -water is where it is only because of low elevation -crust, mantle, inner core are all solid. Only outer core is liquid -when mantle melts, creates basalt, basalt melts to make granite -core (made up of iron), outer = liquid, inner = solid -two kinds of surface: continents, oceans -two kinds of crust: thick and light, thin and dense Plate Tectonics -Alfred Wegener studied ancient climate, very interest in why there were fossils of tropical plants in arctic -Died in Greenland expedition (1930) -Sir Harold Jeffreys, British, objected to Wegener’s theory of continental drift arguing that the mantle was too strong for any conceivable driving force, stalled plate tectonics for 40 years -Wegener suggested that continents plowed through oceanic rocks -Emile Argand, amplified Wegener’s theory, looked at Alps, found folded sheets of rock thrust over the rocks beneath (nappes) -only way this could happen was having Italy plow into Europe -found same thing in Himilayas -Arthur Holmes and convection, proposed that rocks flow because they are heated from below and cooled from above (1928) -rocks are viscoelastic, elastic solid, slow pushing = flow, fast pushing = breakage -mantle rocks move few centimeters per year -takes 100 mil. Years to flow from the top to the bottom of the mantle
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-4.6 billion years of Earth -oldest rocks 4.4 billion -life forms 500 mil. Years ago -oldest oceanic seafloor 200 Myr, -extinction of dinos 65 Myr. -Humans emerge 1-4 Myr. -Earth’s mantle contains radioactive elements which produce heat -Heat causes interior to be warmer than surface (why convection occurs) -convection causes motion at surface -hot rising, cold sinking. Hot air rising causes rocks to go to either side, which pushes material at surface away. Things going down, material converges on that point -Smashing materials = mountains, faults, etc. -rocks are cold at surface and don’t want to flow, surface tries to stay immobile. Surface breaks into large chunks called plates -Pacific = biggest plate, fastest moving -plate boundaries seem to run right down the middle of oceans -continental edges and plate boundaries = very little connection Clues of Plate Tectonics -continents had to have moved around in the past -flora and fauna placement = clue of continental drift -identical rock formations on 2 different continents
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ESS8 lecture - 9/27-San Andreas fault = Pacific and North...

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