The plate Tectonics theory was formulated in the 1960s to explain the phenomena of continental drift and seafloor spreading, and the formation of the major physical features of the Earth’s surface. The Earth’s outermost layer is regarded as a jigsaw of rigid major and minor plates up to 100 kilometers thick, which move relative to each other, probably under the influence of convection currents in the mantle beneath. Major land forms occur at the margins of the plates, where plates are colliding or moving apart – for example, volcanoes, fold mountains, ocean trenches, and ocean ridges.
At times, the crust crumples gradually to form ranges of Fold Mountains such as the Himalayas. Andes (South America) and the Rockies (North America). Sometimes two plates will slide past each other – as in the San Andreas Fault, California, where the movement of the plates sometimes led to sudden jerks, causing the earthquakes common in the San Francisco-Los Angeles area. Most of the earthquake and volcano zones of the world are, in fact, found in regions where two plates meet or are moving apart.
According to the theory of continental drift in geology, about 250 million years ago, the Earth consisted of a single large continent (Pangaea), which subsequently broke apart to form the continents known today. During that time, the rest of the Earth was covered by the Panthalassa Ocean. Later on Pangaea split into two land masses – Laurasia in the north and Gondwanaland in the south – which subsequently broke up into several continents. These then drifted slowly to their present positions.
The existence of a single “supercontinent” was proposed by German meteorologist Alfred Wegener 1912. (There are reports that well known scientists made similar observations centuries ago.) Plate Tectonics was formulated by Canadian geophysicist John Tuzo Wilson and has gained widespread acceptance among earth scientists.