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German meteorologist and geophysicist
Theorized that all the present continents were once part of a super-continent – “Pangaea”
Formed 300 mya Split apart 200 mya
Alfred Wegener
People at Wegener’s time did not accept this theory because he did not know what caused the plates to move
It wasn’t until the 1950 that scientific advances lent more support to the theory of “Continental Drift”
Theory Rejected
Ocean floor mappingConducted by the US in the 1950sAccurate mapping of a continuous chain of
ridges, 75 000 km long, under the world’s oceansMid-Atlantic Ridge – almost exactly midway
between the Americas & Europe and AfricaIt was concluded that the ridge was where the
continents were moving apartStudy conducted by the Glomar Challenger 1968
dated rocks around the ridge The closer to the ridge the younger the rocksThere are no rocks in the oceanic crust that are
greater than 150 million years old
The New Discoveries
Underwater mapping showed that the continental shelves fit more closely together than previously thoughtMuch closer than the continents themselves fit
This was Wegener’s idea
Seismological records (1950s and 1960s)Earthquakes are concentrated in a much
smaller areas than formerly suspected Mainly along deep ocean trenches, the ocean
ridges, and at other points of contact between the plates of the earth’s crust
Earth magnetism (1950s)In North America the magnetic “needles”
pointed to a different magnetic-pole location than the needles in rocks of the same age in Europe