PLATE TECTONICS IS A geological theory that explains many important features of the Earth’s surface through the movement of sections of the crust, known as plates. Among the observed data explained by plate tectonics are the known similarities of features on the east and west sides of the Atlantic Ocean, similarities of plant and animal species in areas now too distant for migrations, the locations of volcanoes and earthquakes, the formation of mountain ranges, and the existence of the Mid-Atlantic Ridge. According to plate tectonic theory, the Earth’s crust is made up of approximately 30 rigid sections or plates of various sizes. For instance, the Pacific Ocean is mostly 1 huge plate, and the major continents each lie on their own plates. Very small plates such as the Gorda Plate in the Pacific Northwest are believed to be the last remnants of ancient plates. Plates lay over a stratum of hot, elastic rock known as the mantle. Temperatures in the mantle range from 2,400 to 2,600 degrees F (1,300 to 2,000 degrees C), and currents within the mantle drive a slow movement of the plates, at the rate of about 4 inch (10 centimeter) per year. Although this movement is small in human terms, observable only with sophisticated scientific measurements, over millions of years plates can move great distances, even from 1 pole to the other.