History of Plate Tectonics

Continental Drift

Continental Drift• The hypothesis of how the continents were all

once together and then split apart and drifted to their current location.

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Early Thoughts• Elie de Beaumont (1829)

o Idea: Earth was contracting stress from this caused mountain building

• Eduard Suesso Austrian geologisto Idea that the southern continents formed a single giant

continent called Gondwanaland (or Gondwana)• Earliest idea of Earth crust was the

continents were fixed and the ocean basins were ancient features

Alfred Wegener• Born in Germany in 1880• Doctorate of astronomy in 1905• Served at the aeronautical observatory at Lindenberg.• Was injured shortly after joining the German army in WWI• After the war, he did research in meteorology in Hamburg,

Germany, for German government.• He was a professor of meteorology at the University of Graz

in Austria from 1924 to 1930. • 1915 published “The Origin of Continents and Oceans”

o Introduced the idea of continental drift, the continents move.

• He went on 4 polar expeditions between 1906 and 1930. On the last of these expeditions, he visited Greenland to try to determine the thickness of the Greenland ice sheet and the rate of drift of Greenland. At the end of that expedition, he died while rescuing some colleagues.

Wegener’s 3 main ideas on

Continental Drift

Wegener’s 1st Idea

• Coastlines seemed to fit together, especially South America and Africa.

• One land mass called Pangaea– Greek meaning ‘all land’

• Pangaea split into two separate continents: Gondwanaland (Gondwana) to the south and Laurasia to the north.

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Animation clips• http://www.youtube.com/watch?v=WaUk94AdXPA

&safety_mode=true&persist_safety_mode=1&safe=active

• http://www.youtube.com/watch?v=zjVDR5FZd4w&feature=related&safety_mode=true&persist_safety_mode=1&safe=active

• http://www.youtube.com/watch?v=NYbTNFN3NBo&feature=related&safety_mode=true&persist_safety_mode=1&safe=active

Wegener’s 2nd Idea

• Geological evidence• Glacial deposits (tillites)– Scraping marks from the ice sheets during the Late

Paleozoic glaciation were found on southern Africa, Australia, South America, India and Antarctica suggested that all were connected near the South Pole.

Glacial Striation, scraping

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Ice sheets during the Late Paleozoic glaciation (now termed the Gondwana Ice Age)

Wegener’s 3rd Idea

• Fossil evidence– Similar plant and animal fossil from the Paleozoic

time period in the southern continents and between North America and Europe

Alexander du Toit (around 1937)

• South African geologist• Supported Wegener’s ideas• With geological evidence he put Gondwana near the South Pole

and the Northern landmass (America, Greenland, Europe, and Asia) at the equator.– Northern landmass named Laurasia– Evidence coal deposits.

• Proved paleontological evidence– ‘Mesosaurus’: Permian freshwater reptile occurred in rocks of the

same age in both Brazil and South Africa.– Freshwater can’t survive in marine type environment, so how did it get

from South Africa to Brazil without going through the ocean?

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Wegener’s Idea of how Continents move

• Earth’s crust was made of two pieces– Upper had low density (continent)– Lower had high density (ocean basin)

• The upper piece ploughed through the denser crust piece.

Why Alfred Wegener’s Ideas were accepted

O Could not fine a convincing mechanism to explain how the continents moved.

O Physicists convinced geologists that Earth’s outer layers were too rigid for continental drift to occur.

O Wrong on how fast the continents were moving

Arthur Holmes• He suggested convection currents “dragged the

two halves of the original continent apart, with consequent mountain building in the front where the currents are descending, and the ocean floor development on the site of the gap, where the currents are acceding.”

• He knew he couldn’t fight the physicists ideas without an outside independent source of evidence to back up his hypothesis.