This is a drawing of the Earth's lithosphere.
Click on image for full size
Clues to Plate Movements
Many kinds of surface features provide evidence of a sliding lithosphere.
When two plates move apart, rising material from the mantle pushes the lithosphere aside. Two types of features can form when this happens. At mid ocean ridges, the bottom of the sea comes apart to make way for new ocean crust formed from molten rock, or magma, rising from the mantle. Continental rifts form when a continent begins to split apart (the East African Rift is an example). If a continental rift continues to split a continent apart it can eventually form an ocean basin.
When two plates move towards each other, several features can form. Often, one of the plates is forced to go down into the hot asthenosphere at a subduction zone. Volcanoes may form when a subducted plate melts and the molten rock comes to the surface. If neither plate is subducted, the two crash into each other and can form huge mountains like the Himalayas.
If these features are found on a planet's surface, they provide evidence that the planet's surface is in motion. There are only a few other planets that have a surface in motion.
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