Erosion is more important on Earth than on the other planets. Volcanism is important on Earth because it not only created our atmosphere but it also reshapes the surface. Tectonics also shapes our surface, causing ridges, valleys, mountain ranges, etc. Other planets have tectonics going on, but we may be the only one with plate tectonics. 2 million years ago.
Plates move at rate of a few centimeters per year.
More than a dozen plates. Rock is carried up from the mantle to the lithosphere, then dragged back down again. We can date material around the ridges and see that the rock is youngest closest to the ridges. Colliding continental plates will cause mountains like Himalayas and the Appalachians. We'll also eventually lose portions of California for the same reason.