Plate tectonics has shaped the Earth's surface for billions of years: Continents and oceanic crust have pushed and pulled on each other, continually rearranging the planet's façade. As two massive plates collide, one can give way and slide under the other in a process called subduction. The subducted slab then slips down through the Earth's viscous mantle, like a flat stone through a pool of honey.

Source: Ancient Earth’s hot interior created 'graveyard' of continental slabs