Alfred Wegener first hypothesized continental drift in 1915, proposing that the continents were once joined together in a supercontinent over 200 million years ago. In the 1960s, scientists David Beckner and others developed the theory of plate tectonics to explain the movement of continents. Plate tectonics provides geological evidence and conceptual models to explain how and why the Earth's plates have shifted positions over hundreds of millions of years.