In studying this subject, be sure you learn to distinguish two important concepts: 1) continental drift, that is, the idea of continental motion itself; and 2) plate tectonics, the mechanism or force that drives continental motion. Each theory rests upon its own lines of evidence. Together, the theories make a consistent cause-and-effect case to support the animations of Earth's history shown in the videos on this page. The theory of plate tectonics provided an explanation of continental motion, and led to much wider acceptance of the idea that the surface of the earth is in constant motion.
Watch These Videos
First, here is a reconstruction of global continental drift from 540 million years ago (mya) until today.
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Evidence for Continental Drift
Eugene Wegner presented four lines of evidence that today's continents were once part of one large land mass that broke into pieces -- today's continents -- and drifted into their present positions. This video describes that evidence, and how it fits Wegner's interpretation.
Scientists were slow to accept this view, in large part because they could not imagine a mechanism for continental motion.
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Plate Tectonics
What drives the motion of the continents? Mainly, it's convection, the same process that makes a room in your house warmer at the ceiling than on the floor. In the case of Earth, the rising of hot liquids towards the surface pushes the continents around.
Evidence for Plate Tectonics
This video describes Earth's internal structure and the basis of movement within and one the surface of the planet. Most of the evidence is presented in the section called "History". Today, scientists can measure the slow movements of the continental plates, and the rising of mountains. Roughly, the largest of these constant motions are in the range of one inch per year, easily measured by surveying methods, and radar, particularly from satellites. In earthquakes, the motions are sudden and much larger.
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