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Plate Tectonics

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Advances after Wegener

1910s

The invention of echo sounders by the Germans in WWI was primarily for military use but had many scientific benefits as well.  Scientists used echo sounders to measure ocean depths and realized that the seafloor was much more rugged than believed.

 

1940s

1947 – U.S. research ship Atlantis discovered that sediments in the Atlantic Ocean are much thinner than originally thought

Harry Hess was a Princeton Professor and Navy Reservist. When the US entered the war they called upon Captain Hess to serve. He got command of his own ship (the USS Cape Johnson) and some cool new toys to play with (echo sounders and magnetometers, to name a few)! Harry kept instruments running 24/7. Why? Well, they were at war, but it was also to keep the men busy and not too bored. As a result, Harry – and his crew – did the following:

That last item bothered Hess. Flat-topped mountains are created by erosional forces. Yet there are no erosional forces to do this at the bottom of the ocean. So, how did they get there?

 

1950s

Marie Tharp (1920-2006) was a cartographer, geologist, and oceanographer.  The arrival of WWII enabled her a rare opportunity:  to get an advanced degree in Geology at the University of Michigan.  Later, while working as a research assistant at Lamont Geological Laboratory at Columbia University in New York, she began to collaborate with then-graduate student Bruce Heezen.  He'd go out on the ship and gather SONAR readings, and she'd make sense of the data back in NY. 

Her first achievement was the discovery of an underwater ridge, called the Great Global Rift,  that ran 40,000 meters along the seafloor through the Pacific, Indian, and Atlantic Oceans.  Tharp believed that the mountain range noted by Thomson, Maury, and others (see the previous page) was a rift valley, and could support Wegener's Continental Drift Hypothesis.  Her ideas were largely ignored.

In 1957, Tharp and Heezen published the first physiographic map of the North Atlantic Ocean.  This was followed by a map of the South Atlantic ocean floor in 1961, one of the Indian Ocean floor in 1964,  and finally The World Ocean Floor in 1977.  These maps proved that the ocean floor was not flat and featureless, but contained ridges and valleys and other features, just like on land.  

Most scientists - nearly all of them male - continued to dismiss Tharp's theories.  It wasn't until ocean explorer Jacques Cousteau set out to disprove her ideas and ended up realizing that she was right that things began to change. 

A map of the Mid-Atlantic Ridge by Marie Tharp

Image source:  "A map of the mid Atlantic Ridge by Marie Tharp" by Smithsonian is licensed under CC BY-NC 4.0

 

 


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copyright Sonjia Leyva 2022

CSULA | PCC