The theory states that Earth’s outermost layer, the lithosphere, is broken into 7 large, rigid pieces called plates: the African North American, South American, Eurasian, Australian, Antarctic and Pacific plates. Several minor plates also exist, including the Arabian, Nazca, and Philippines plates.
The plates are all moving in different directions and at different speeds (from 2 cm to 10 cm Per Year about the speed at which our fingernails grow) in relationship to each other. The place where the two plates meet is called a plate boundary. Boundaries have different names depending on how the two Plates are moving in relationship to each other.
These plates lie atop a layer of partly molten rock called the asthenosphere. The plates can carry both continents and oceans, or exclusively one or the other. The Pacific Plate, for example, is entirely oceanic.
Continental .plates are composed mainly of granite, while oceanic plates are mostly basalt, which is considerably heavier. Essentially, the continents are lighter and more buoyant; hence, they float higher on the earth’s mantle than the ocean’s crust does.
Convergent Boundary :
These are the places where plates crash or crunch together are called convergent boundaries also known as collisional boundaries. When plates converge, one slips under the other and is said to be subducted. At depths from 185 to 435 miles beneath the earth’s surface, the subducted parts of the plate melt and become part of the molten mantle. As new plate material is being formed continuously, and the excess is melted into magma, the earth’s rocky crust is constantly recycled.
When two continental Plates converge the two interact to create mountain ranges.
Places where plates are coming apart are called divergent boundaries also
called as spreading centres. Where a divergent boundary crosses the land, the rift valleys get formed which are typically 30 to 50 kilometers wide. Examples include the East Africa rift in Kenya and Ethiopia, and the Rio Grande rift in New Mexico. Oceanic ridges rise a kilometer or so above the ocean floor and form a global network tens of thousands of miles long. Examples include the Mid-Atlantic ridge and the East Pacific Rise. Plate separation is a slow process, e.g. Divergence along the Mid Atlantic ridge causes the Atlantic Ocean to widen at only about 2 centimeters Per Year.
Transform boundary :
Places where plates slide past each other are called transform boundaries. The plates on either side of a transform boundary are merely sliding past each other and not tearing or crunching each other.