Only since the 1960s have scientists begun to understand that the Earth is a great, living structure. Some experts say this new understanding is one of the most important revolutions in scientific thought. The revolution is based on the work of scientists who study the movement of the continents -- a process called plate tectonics. Earthquakes are a result of that process. Plate tectonics is the area of science that explains why the surface of the Earth changes and how those changes cause earthquakes.
Scientists say the surface of the Earth is cracked like a giant eggshell. They call the pieces tectonic plates. As many as twenty of them cover the Earth. The plates float about slowly, sometimes crashing into each other, and sometimes moving away from each other.