Plate Tectonic theories

Alfred Wegener

• Proposed the theory of continental drift. He suggested that all the plates were joined together in a super continent called Pangaea which drifted apart.
• Wegener based his theory on geological evidence and fossil records.
• But couldn't back it up with a mechanism that explained how the continents moved.
• But in the 1950s, palaeomagnetism provided evidence that supported continental drift.
• And in the 1960s the process of sea floor spreading was discovered-it provided the mechanism for continental drift.

Evidence for Continental drift

• Geology
• -Areas of South America and Africa have rocks of the same age and composition- if you fit these continents together, the distribution of the rocks matches up.
• -You can also match up mountain ranges, eg Mountains in Scotland, Norway, Sweden and Finland are similar to the east coast of North America.
• -These rocks and mountains must have been formed under the smae conditions and the same place in order to match so well- this would only be possible if the continents were once joined.

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• Fossil Records
• By fitting land masses you can match up the distribution of some fossils eg fossils of Lystrosaurus and Mesosaurus
• Living Species
• The same living organisms can be found on different continents.
• Climatology
• There's evidence that the past climates of some continents were similar, despite being thousands of miles apart now. This suggests that they were located together and in different places
• Poalaeomagnetism
• Study of earths magnetic field
• Once every 200,000 years the Earth's magnetic field reverses polarity
• Provides evidence for sea floor spreading
• As magma erupts from the mid-ocean ridges, magnetic minerals in the molten rock align themselves with the direction of the earths magnetic field.

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