Transcript for Exotic Terrane, segment 09 of 12

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Geologists search for more evidence to support their exciting new findings. They use many types of geologic investigations, both in the field and in the lab. Paleomagnetism uses the magnetic properties of rocks to determine their location when they first formed. Mass spectrometry reveals the kind of environment that rocks formed in as well as their ages. A technique called potassium argon dating is also used to determine the age of certain rocks.

As scientists had hoped, these studies provided supporting evidence for their new geologic theories. It is now thought that much of western North America did not form as part of the continent. Large parts are made up of oceanic islands, coral reefs, and other sea floor fragments. These exotic terranes were brought in from the ocean by the relentless force of plate tectonics.