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Theory of Plate Tectonics

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Iris Demboski

on 23 September 2013

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Transcript of Theory of Plate Tectonics

The Mesosauraus was a freshwater animal
Fossils of this animal have only been found in South America and Africa
The Cynognathus was a Triassic land reptile
(fossils of this creature have only been found through the middle parts of South America and Africa)
The Glossopteris was a seed fern that was found in bands within all southern continents ( South America, Africa, Antarctica, India and Australia)
The Triassic land reptile the Lysotrosaurus had fossils found in
Africa, India and Antarctica)
This fossil evidence leads us to believe that at one point these Southern continents were all connected as one, because unless these animals were physically moved to a different area of the world, they could not cross the ocean and survive. Wegener was one of the first scientists to notice this trend between South America and Africa.
(n.d., n. pag. <http://earthobservatory.nasa.gov/Features/Wegener/wegener_4.php>)

Born November 1, 1880 in Berlin Germany
Began to develop interests in meteorology and arctic exploration
Director of Meteorological Research Department of the Marine Observatory
In 1912 he took a trip, which is recorded as the longest ice cap crossing
Father of "Plate Tectonic Theory"
Died in 1930 from heart attack due to overexertion
Alfred Wegener
Wegener's Theory
Wegener was the first scientist to study how South America's and Africa's continental shelves were related. Through his studies, he discovered that these two continents continental shelves (submerged border of a continent in shallow ocean water) matched better than their visible coastline. Through fossils, maps and the study of rock formations, Wegener was able to create a supported theory of how South America and Africa were once connected. This soon led to his idea of continental drift.
Evidence of Continental Drift
Harry Hess
Harry Hess was born on May 27, 1906, in New York City. Hess received a Bachelor of Science degree in 1931 from Yale University, and a Ph.D. from Princeton in 1932. After he graduated, he taught for one year at Rutgers University. In 1934, Hess became a professor at Princeton, where he became the head of the Geology department in 1950. Harry Hess died of a heart attack on August 26, 1969 in Massachusetts.
Sea-floor spreading
This was a type of recycling process. In 1946 Hess had discovered that hundreds of flat-topped mountains, perhaps sunken islands, shape the Pacific floor. Harry Hess had proposed in 1960 that the movement of the continents was a result of sea-floor spreading.
Earth's History of Magnetic Reversals
Glaciers and Magnetic Pole Movement

Wegener observed how continents somewhat float in oceans, meaning their composition must be less dense than that of the volcanic basalt that is the foundation of the ocean floor. in order to maintain equilibrium, Wegener noticed the continents have to shift. This process is called isostasy. An example of this shift is the Northern Hemisphere that sunk due to the weight of continental ice sheets and rose again after the ice had melted some 10,000 years ago.
Rock Types and Mountain Ranges
Wegener began to notice that in addition to similar fossil evidence and magnetic pole shift, the two continents shared similar geological features. Based off the cooling- contracting of the earth, mountain ranges usually occurred in narrow bands along the edges of continents. Wegener noticed that Africa and South America shared similar rock formations and composition. This lead him to believe that at what one point the continents were all connected. He called this Pangea and believed that about 200 million years ago is when they started to move to their present positions.
In the Early 20th century, paleomagnetists (people who study the Earth's ancient magnetic field), recognized that rocks generally belong to two groups according to their magnetic properties. One group is called normal polarity, characterized by the magnetic minerals in the rock having the same polarity as that of the Earth's present magnetic field. This would result in the North end of the rock's "compass needle" pointing toward magnetic north. The other group, however, has reversed polarity, indicated by a polarity alignment opposite to that of the Earth's present magnetic field. In this case, the north end of the rock's compass needle would point South. How could that happen? This answer lies in the magnetite in volcanic rock. Grains of magnetite -- behaving like little magnets -- can align themselves with the orientation of the Earth's magnetic field. When magma (molten rock containing minerals and gases) cools to form solid volcanic rock, the alignment of the magnetite grains is "locked in," recording the Earth's magnetic orientation or polarity (normal or reversed) at the time of cooling.
Works Cited
Work Cited
Mathez, Edmond A. "Harry Hess: One of the Discoverers of Seafloor Spreading." Amnh.org. N.p., 2000. Web. 20 Sept. 2013. <http://www.amnh.org/education/resources/rfl/web/essaybooks/earth/p_hess.html>.

PBS. "Hess Proposes Sea-Floor Spreading." Pbs.org. N.p., 1998. Web. 21 Sept. 2013. <http://www.pbs.org/wgbh/aso/databank/entries/do62se.html>.

USGS. "Developing the Theory." Usgs.gov. U.S. Geological Survey, 05 May 1999. Web. 19 Sept. 2013. <http://pubs.usgs.gov/gip/dynamic/developing.html>.

USGS. "Harry Hammond Hess." Usgs.gov. U.S. Geological Survey, 05 May 1999. Web. 20 Sept. 2013. <http://pubs.usgs.gov/gip/dynamic/HHH.html>.

"Greatest Discoveries." Science Channel. N.p., n.d. Web. 22 Sept. 2013. <http://science.discovery.com/tv-shows/greatest-discoveries/videos/earth-science.html>

"Alfred Wegener : Feature Articles." Alfred Wegener : Feature Articles. N.p., n.d. Web. 22 Sept. 2013. <http://earthobservatory.nasa.gov/Features/Wegener/wegener_4.php.>

"Alfred Wegener." Welcome to the Dutton E-Education Institute! N.p., n.d. Web. 22 Sept. 2013. <https://www.e-education.psu.edu/earth520/content/l2_p10.html>
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