Continental drift and seafloor spreading

madugundurukmini By madugundurukmini, 20th Aug 2014 | Follow this author | RSS Feed | Short URL http://nut.bz/2rwjqwrl/
Posted in Wikinut>Guides>Science>Physical Forces

Unlike the continental drift theory, which essentially neglects ocean basins, sea -floor spreading is centered on the activity beyond our direct view.

Wegener's proposal encountered a great deal of hostile criticism

The revolutionary theory of the Continent Drift, propounded by Alfred Wegener, suggested that a super continent called Pangaea (meaning `all land') once existed. It hypothesized that about 200 million years ago, this super continent began breaking into smaller continents, which then `drifted' to their present positions. The amazing fit of the coastlines of South America just as in a jig -saw, climate similarities, fossil evidences and rock structures all seemed to support the idea that these, now separate land masses, were once joined.

Wegener's proposal encountered a great deal of hostile criticism. Very little new was shed on the continental drift hypothesis between the time of Wegener's death in 1930 and the early 1950s. But thereafter vast strides were made that forced critics to view the Continental Drift theory in a new light. The theories of palcomagnetism or fossil magnetism and Polar wandering (wandering of the magnetic poles) re- in-forced Wegener's idea.

In the early 1960s, all of these newly discovered facts were put together by Harry Hess into a hypothesis called Sea -floor spreading. Unlike the continental drift theory, which essentially neglects ocean basins, sea -floor spreading is centered on the activity beyond our direct view. Hess proposed that the ocean ridges are located above up welling portions of large convection cells in the mantle. As rising material from the mantle spreads laterally, sea floor is carried in a conveyor- belt fashion away from the ridge crest. Further, tensional tears at the ridge crest produced by the diverging lateral currents provide pathways for magma to intrude and generate new oceanic crust. Thus, as the sea floor moves away from the ridge crest, newly formed crust replaces it, making the ocean floor seem forever young! By late 1960s, geologists began reversing their stand on the issue of restive Earth. The tide of scientific opinion had indeed turned in favor of a mobile Earth!

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