2.4: Evidence for Plate Tectonics

In 1912, after many years of research, Alfred Wegener proposed that the continents drifted across the Earth. His evidence included the fact that the continents seem to fit together, and similar fossils and glacial patterns were found on two different continents. Despite this evidence, he could not figure out what was causing this movements of the continents. Unfortunately, Wegener passed away before any new discoveries were made about the mechanisms behind this movement of continents across the ocean.

New theories started to arise as more evidence was collected. A particularly strange discovery was made when scientist discovered that the rock age of the ocean was less than 200 million years old. This was very different from the much older rock age on land. From this, scientist found that in the ocean, there were subduction zones where the old ocean crust was subducted into deep ocean trenches. New ocean crust was then created at the mid ocean ridge. This was called sea floor spreading. More evidence was needed to support this theory, however. When scientist mapped out earthquake patterns around the world, they discovered that the location of earthquakes were associated with the locations of the subduction zones. This further provided evidence for plate tectonics. More evidence came when scientist examined the sea floor and saw that there were reversals of polarity of Earth’s magnetic field that was in a striped pattern. The strips of polarity reversal were mirror images on each side of the mid- ocean ridge. All this evidence complied together convinced scientists of the existence of plate tectonics and continental drift.

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