Early in the 20th century, Alfred
Wegener suggested that the all the
world’s continents had once been part of a single supercontinent,
which he called Pangea.
Over hundreds of millions of years, the continents drifted apartand
even now they continued to drift (very slowly) across the face of the
planet. Other geologists were dubious, but over time they found enough
evidence to prove Wegener correct.
This theory is now called plate
tectonics. The plates "float"on the asthenosphere,
a layer of soft, molten rock, and are pushed about by convection
currents rising up from the mantle below.
The plates move just an inch or two each year. But that's enough to create
enormous stress when two plates run into each other.