In the early 20th century, geologists began to realize that the Earth’s outer crust is not one solid piece like an egg’s shell. The crust is broken up into giant tectonic plates that ride atop the magma, hot melted-rock material that makes up much of the interior of the Earth. Over millions of years, the continents drift into new configurations.
Convection in the molten rock of Earth’s mantle drives the movement of the plates. Hotter material rises to the surface, while cooler material sinks toward the core. This creates pushing and spreading apart at mid-ocean ridges and subduction (sinking) of one plate under another at subduction zones.
In the early 20th century, German researcher Alfred Wegener noted that fossil remains of the same extinct animal or plant can be found across several continents that are not now adjacent to one another. This suggests that in the distant past, the configuration of continents was different than it is today, a theory Wegener called “continental drift.”