Continental Drift Plate tectonics helps explain the theory of Continental Drift. That theory states about 175 million years ago all the continents of the earth moved together in a single giant landmass. Scientists have looked for evidence to support the idea that the land was once joined, and use several factors in their studies. If land once was joined, the rocks should share common characteristics across the original divide. As old as the earth is, chances are that the continents have all bumped into each other many times.
Some scientists believe that the land masses have come together more than once.
In reconstructing the ancient world, it takes more than just fitting coastlines like pieces of a puzzle. It is better to fit the continents together not at the coast where active processes are changing the landscape, but instead at the continental shelf, which extends into the ocean, and then has a sharp drop to the ocean floor. The best examples of continents fitting together are the east coast of Brazil in South America, and the southwest coast of Africa. Paleomagnetism is a fascinating remainder of magnetic traces preserved in rocks. Iron minerals in volcanic or molten rocks will line up in the direction of the earth's prevailing magnetic field, and when the rock cools, the particles are fixed permanently like tiny compass needles in the rock.