Geology: Plate Tectonics

Continental Drift

In the early 1900’s, German Meteorologist Alfred Wegener theorized that the continents were once connected in a super-continent and they have been drifting across the Earth’s surface ever since. Wegener’s super-continent was named “Pangea” and is thought to have existed about 250 million years ago. Wegener had four major pieces of evidence supporting his theory:
  • The Apparent Fit (South America and Africa appear to fit together like puzzle pieces)
  • Fossil Correlation (The same exact fossils are found on opposite sides of the Atlantic ocean)
  • Rock Correlation (The same exact rocks/mountains are found on opposite sides of the Atlantic ocean)
  • Past Climate Data (There is evidence of glaciers in tropical locations, and deposits of coal in Antarctica)

The theory of Continental Drift was not accepted because it failed to explain what was causing the continents to move (no mechanism).
 
Earth's Interior

Our model of the Earth’s interior is based on the study of seismic waves. The Earth has a layered structure because when it formed 4.6 billion years ago, it was mostly melted, allowing more dense materials to sink to the center and lighter materials to float to the surface. It is made of the following layers:
  • Crust, the solid, rocky surface (Continental crust is thick, low density, and composed of granite, oceanic crust is thin, high density, and composed of basalt)
  • Mantle, composed of the rigid mantle, plastic mantle, stiffer mantle (The Crust and the Rigid Mantle make up the lithosphere, the Moho is the boundary between the crust and the rigid mantle, and the Plastic Mantle is partially melted and known as the asthenosphere
  • Outer Core (liquid iron)
  • Inner Core (solid iron and nickel)

As depth within the Earth increases, density, pressure, and temperature increase.
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