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study of the earth
Founder of geology
Created "great geological cycle" : many cycles of weathering, erosion, deposition of sediment, transformation of sediment into rock and uplifting that starts the weathering again
The earth is a heat engine with internal heat melting rocks to form magma and flows out as basalt.
Theory of uniformitariasm : the process now operating on and in the earth have operated in the past. The earth's internal heat forms mineral veins. "earth has no beginning nor end"
Age of the earth
4.55 billion or 4.6 billion
made of basalt, thin ~ 10 km thickness, made at Rud-Ocean-Ridges, destroyed at subduction zone. Oldest is 200 Ma, density 2.0 g/cm3
Made of granite, contains great diversity of rocks. Thick (35 km thick) and up to 70 km thick. Oldest is 4.2 billion years old.
Mantle and core
outer core is liquid Fe-Ni, mantle is 2,700 km thick
Crust: relatively thin outer layer4-70 km thick, low density, 2.7-.0 g/cm3, active earthquakes, volcanoes, moving plates etc.) chemically different from layer below it. Divided into: ocean crust 4-10 km thick composed of black volcanic rock *basalt* and continental crust which is older, thicker, and less dense.
Mantle: thick layer below the crust which is 2970 km thick and 84% of earth's volume. Moho is area between crust and mantle
Core: central layer of earth 3,500 km thick. Liquid outer core and solid inner composed mainly of nickle and iron. The magnetic field is generated by spinning outer core. Oxygen and sulfur also found in core.
Lithosphere: the crust and upper right mantle 100 km thick broken into a series of plates
Continental drift (Alfred Wagener)
Alfred Wagener wrote book " Origins of Continents and Oceans"
Believed supercontinent Pangea existed 200 Ma and continents broke apart and drifted to current positions.
Ideas originally rejected.
Fit of S. America and Africa.
Fossil evidence of mesosaurus found in S. America and Africa which was incapable of swimming the Atlantic Ocean.
Glosserpteris, fern found in Africa Australia, India and South America.
Similar rock types and structures: Appalachan disappear at Newfoundland and reappear in British Isles and Scandanavia.
Paleoclimates: southern land mass fit together at south pole and form glaciers.
Sea floor spreading (Harry Herman Hess)
Captain during WWII and Princeton professor of the navy that used sonar to survey Pacific Ocean floor. Built on the ideas of Wegener and Holmes. Published paper "History of Ocean Basins". Believed that origin of new seafloor was at Mid Ocean Ridges. Movement of sea floor away from ridge to the trench. At trench old sea floor sinks back into mantle.
Author Holmes - New age of rocks (billions of years old) mantle convection cause continental drift
Proposed that radioactivity inside the earth would heat them and make them plastic and less dense so that they would rise upward toward the surface.
Near the surface the rocks would cold and become more dense and sink back into the lower mantle. Continental drift is caused by flow of mantle that carriers the continents.
J. Tuzo Wilson and transform faults are the third plate boundary, plumes causes strait chain of volcanoes in ocean, Wilson cycle of super continents
Georgia's location 200 Ma when it was part of Pangaea
- near the equator
Paleomagnetism- Magnetite, Curie Point, direction to poles, dip needle, polar wondering
Geomagenetic Reversals- north and south magnetic Lines (stripes) of force switch positions, normal polarity, reverse polarity, magentic pattern about a ridge