Plate tectonics is the widely accepted theory that the Earth's crust is divided into several sections that float around on the mantle - the mostly solid layer between the core and the crust. But how they move around has been a subject of much debate among scientists since the theory was first accepted in the 1950s. The sections, known as plates, move at a rate of about 2 to 5 centimeters per year, which is a similar speed to how fast your fingernails grow. When they grind past each other, it's called a transform plate boundary, which can cause earthquakes. When they move away from each other, it's known as a divergent boundary, where lava spews out, and volcanoes can form. Sometimes, when they