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Timeline of Plate Tectonics Theory
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Timeline of Plate Tectonics Theory
Drill Ship 1960's
Alfred Wegener 1912
The Glomar Challenger was a drill ship in the 1960's which collected crustal samples and then dated them. It investigated 624 sites in the Atlantic, Pacific, and Indian oceans which supported the theory of plate tectonics by providing evidence of continental drift and seafloor renewal.
Early in the 20th century, Alfred Wegener proposed that the continents were once compressed into a single protocontinent which he called Pangaea- this means 'All Lands'. He thought that over time they have drifted apart into their current distribution.
Wegener had evidence that South America and Africa used to be one piece of land:
The same types of fossilised animals and plants are found in South America and Africa.
The shape of the east coast of South America fits the west coast of Africa, like pieces in a jigsaw puzzle.
Matching rock formations and mountain chains are found in South America and Africa
John Tuzo-Wilson 1963
Pre Wegener
Harry Hess 1940's
Before Wegener developed his theory, it was thought that mountains formed because the Earth was cooling down, and in doing so contracted. These contractions would have apparently formed wrinkled and bulges in the earths crust which we see as mountains.
Harry Hess was a professor of geology at Princeton University and he used to serve in the US navy during world war 2- this sparked his interest in the oceans. He published ‘The History of Ocean Basins' in 1962, in which he outlined a theory that could explain how the continents could actually drift. This theory later became known as ‘Sea Floor Spreading'.
He discovered that the oceans were shallower in the middle and discovered 'Mid Ocean Ridges', raised above the surrounding generally flat sea floor. He found out that oceans grew from their middle's with magma oozing up from the Earth’s mantle along the mid ocean ridges.
Hess believed that ocean trenches were the locations where ocean floor was destroyed and recycled- like Wegener, his theory needed confirmation before it was believed.
Tuzo Wilson proposed that plates might move over fixed ‘hotspots’ in the mantle, forming volcanic island chains like Hawaii.
Two years later, he followed this theory up with another- this concerned a third type of plate boundary called 'Conservative Plate Boundaries', this was when two plates moved horizontally to eachother. The most famous example is probably the San Andreas Fault between the North American and Pacific plates.