Continental Drift Theory
Basically, the continental drift theory asserts that land masses which were once whole(Pangea), float along a layer of molten lava. These plates, or land masses collide and form new land masses. The movement of these plates is caused by convection currents which occur when the magma rises to the surface and cools. This cool is pushed down through a process called subduction.
The Different Plates
It is believed that the crust, beneath the oceans as well as the continents, togehter with the uppper part of the mantle is divided into huge slabs called plates. It is the movement of these plates which the Continental Drift Theory seeks to explain.
There are eight identified major plates plus an assortment of smaller ones. The major plates include the Eurasian plate, the African plate, the North American plate, the South American pate, the Antarctic plate, the Indoaustralian plate, the Pacific plate and the Nazca plate.
Sea Floor Spreading
Sea floor spreading is the processs in which the ocean floor is extended when two plates move apart. As the plates move apart, the rocks break and form a crack between the plates. Earthquakes occur along the plate boundary. Magma rises through the cracks and seeps out onto the ocean floor like a long, thin , undersea volcano.
As magma meets the water, it cools and solidifies, adding land mass to the edges of the side-ways moving plates. As this magma cools and piles up along the crack, a long chain of mountains forms gradually on the ocean floor. This chain is called an oceanic ridge.