plate tectonics

The Earth is always changing. Mountains form and erode away. Volcanoes erupt and grow larger. Earthquakes shift the land. Oceans grow and even continents move. What causes all this activity? The Earth's thin, fragile outer shell is broken into large pieces called "plates." These plates slowly move, floating on a layer of hot mantle below. This movement, or tectonic activity, is constantly changing the surface of the Earth.

Image credits: main image, courtesy of AMNH; Ed Mathez: courtesy of AMNH.