Researcher Alfred Wegener developed the continental drift theory that led to the modern theory of plate tectonics. Because plate tectonics is still a theory, it is hypothesized and not officially discovered or proven.
The theory of plate tectonics is that separate and disconnected plates make up the lithosphere, or outer layer of Earth. Geoscientists believe that these plates move, causing the formation and break up of Earth's continents during hundreds of millions of years. There are eight major plates and many minor plates. The volatile friction within plate boundaries leads to increased seismic activity earthquakes and volcanic eruptions. For example, the highly active San Andreas Fault is part of the boundary between the Pacific and North American plates. Although Wegener first theorized drifting plates in 1912, it was not widely believed until the early 1950s.