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Paleomagnetism

Paleomagnetism refers to the orientation of the Earth's magnetic field. Its study has demonstrated that the Earth's magnetic field has changed in orientation and intensity over time. Its possible because minerals such as magnetite in basalt and other igneous rocks become aligned with the Earth's magnetic field at the time of the rock's solidification.

Paleomagnetic evidence, both reversals and polar wandering data, was instrumental in verifying the theories of continental drift and plate tectonics in the 1960s and 70s.

  • This uneven distribution is the result of coal formation at different times in the geological past, and the drift of the continents to their present-day positions

Distribution

of Coal

The major areas are principally in the Northern Hemisphere; with the exception of Australia, the southern continents are relatively deficient in coal deposits. Permian coalfields are found in the southern continents — South America, India, southern Africa and Australia.

  • Remains of Mesosaurus, a freshwater crocodile-like reptile found in Southern Africa and Eastern South America. It would have been impossible for Mesosaurus to swim between the continents. This suggests that South America and Africa were joined.
  • Cynognathus is an extinct mammal-like reptile. It is found as fossils only in South Africa and South America.
  • Glossopteris was a woody, seed-bearing shrub or tree which fossils are found in Australia, South Africa,South America, India and Antarctica.

Geological Fit

When the geology of eastern South America and West Africa was mapped it revealed that ancient rock outcrops over 2,000 million years old were continuous from one continent to the other. Any areas where there are gaps or overlaps may be explained by :

  • Coastal erosion since continental separation
  • Coastal deposition since continental separation
  • Rises in sea level since continental separation
  • Changes in land level since continental separation

Fossil Reports

There are many examples of fossils found on separate continents and nowhere else, suggesting the continents were once joined. If Continental Drift had not occurred, the alternative explanations would be:

  • The species evolved independently on separate continents
  • They swam to the other continent/s in breeding pairs to establish a second population.
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