Alfred Wegener (1880-1930)

Continental Drift

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

1. Continental Fit

2. Similarities of Rock Sequences and Mountain Ranges

3. Fossil Evidence

4. Glacial Evidence

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