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There is a variety of evidence for the theories of continental drift and…
There is a variety of evidence for the theories of continental drift and plate tectonics
basic structure of the earth
Lithosphere
The section above the asthenosphere
A rigid section sandwiched between the crust and asthenisohere
Asthenosphere
The layer of the crust that extends from 100km down to 300km
Solid, but flows under pressure
Convection currents
Caused by vast amounts of heat generated in the mantle
As a result, the asthenosphere flows carrying with it the solid lithosphere and crust.
Evidence of sea floor spreading from paleomagnetism and the age of sea floor rocks
Paleomagnetism
Paleo magnetism is the ancient record of changes in poles on the earth.
Every 400-500,000 years the poles change, and this is recorded in the rocks on the ocean floor.
Patterns of magnetism were identified the basaltic rocks making up the ocean floor. These showed mirror images of stripes as you moved away from the mid atlantic ridge.
The symmetrical pattern of geo magnetic reversals on either side of mid ocean ridges indicated that as fresh molten rock from the asthenosphere reached the ocean bed, older rock was 'pushed' away from the ridge.
In this way, sea floor spreading moves material across the ocean floors as a 'conveyer belt'.
Age of sea floor rocks
Oceanic rocks get older the further they move apart
Wegeners evidence for continental drift
Case
250 million years ago, a large single continent, Pangea, existed.
This slowly broke apart into two land masses
Movement continued until continents seperated and spread across the globe.
Evidence
Geological
The fit of south america and Africa matched on either side of the atlantic
Evidence of glaciation in southern Africa, Australia, south america, india and antarctica suggested land masses were once joined
Mountain chains show similarity: e.g. in Canada and Scotland
Biological
Similar fossils of
marine **
shellfish** found in australian and indian limestones
Similar fossils found in south america and australia such as
masrupials