![The theory of continental drift is based on the concept that the continental and oceanic crusts are &elipsis; [Credit: © Merriam-Webster Inc.]](http://images.bookrags.com/images/eb/72142.gif)
The theory of continental drift is based on the concept that the continental and oceanic crusts are &elipsis; [Credit: © Merriam-Webster Inc.]Large-scale movements of
continents over the course of geologic time. The first complete theory of continental drift was proposed in 1912 by
Alfred Wegener, who postulated that a single supercontinent, which he called
Pangea, fragmented late in the
Triassic Period (approximately 250–200 million years ago) and that the parts began to move away from one another.
He pointed to the similarity of rock strata in the Americas and Africa as evidence to support his hypothesis. Wegener's ideas received support from the concepts of seafloor spreading and plate tectonics beginning in the 1960s. The modern theory states that the Americas were joined with Europe and Africa until &circa; 190 million years ago, when they split apart along what is now the Mid-Atlantic Ridge. Subsequent tectonic plate movements took the continents to their present positions.
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