# Plate tectonics theory

## Plate tectonics theory

Question - Earth's outer shell is divided into several plates that glide over the mantle. Elaborate.
Plates make up the earth's outer covering, called the lithosphere. There are a few major plates and many more minor ones. The minor Juan de Fuca plate is mainly responsible for the volcanoes that dot the Pacific Northwest of the United States.

Turbulent currents in the molten rocks beneath the plates propel them causing the plates to meet or divide. The movement of the plates creates three types of tectonic margins-

a) convergent - plates move into one another

b) divergent - plates move apart

c) transform - plates move sideways compared to each other.

Plate tectonics is a theory that earth's outer layer is divided into several plates which glide over the mantle and the rocky inner layer above the core. Formulated from the 1950s through 1970s, this theory is the modern version of continental drift which was first proposed by Alfred Wegener in 1912. Hot material near the earth's core rises, and colder mantle rock sinks. This convection is the central force behind plate tectonics.

Mid ocean ridges are gaps between tectonic plates that mantle the earth. Hot magma accumulates at the ridges, giving rise to a new ocean crust and pushing the plates apart. At subduction zones, two tectonic plates meet and one moves beneath the other back into the mantle. The cold, sinking plate along with it, pulls the crust behind it downward.

At the divergent margin, there are two plates which are seen spreading apart, as they are at the seafloor-spreading ridges such as the East Africa Rift.
Transform margins are marked by sliding plates, such as California's San Andreas Fault, where the North America and Pacific plates grind past each other with an almost horizontal motion.

As the continents get pushed around the earth, they occasionally combine to form supercontinents, a single piece of land. Rodinia is one of the earliest supercontinents whose breakup is associated to a global glaciation called snowball earth.

A rather recent supercontinent called Pangaea was formed about millions of years ago. Africa, South America, North America and Europe were joined together, leaving an identifying pattern of fossils and rocks for geologists to understand post the breakup of Pangaea. The puzzle pieces left behind by Pangaea, from various fossils to the matching shorelines along the Atlantic Ocean, worked as the first hints proving that continents move.