Plate Tectonics

is a therory of which was developed to explain the observed evidence for large scale motions of the earths crust The theory surpassed the older theory of continetial drift from the first half of the 20th century and the concept of sea floor spreading developed during the 1960s.

earth interior is made up of two layers: above is the lithosphere comprising the crust. The lithosphere is broken up into what are called tectonic plates. There are seven plates. There are three plate boundaries convergent, divergent, and transform.

The first one convergent occur when two plates slide towards each other commonly forming either a zone. or a continental collision (if the two plates contain continental crust). Deep marine trenches are typically associated with subduction zones. Because of friction and heating of the subducting slab, volcanism is almost always closely linked. The nature of a convergent boundary depends on the type of lithosphere in the plates that are colliding. Whe a dense oceanic plate colldes with a less-dense continental plate, the oceanic plate is typically thrust underneath because of the greater buoyancy of the continental lithosphere, forming a subduction. At the surface, the topographic expression is commonly an oceanic trensch on the ocean side and a mountain range on the continental side.

Divergent boundaries are when two plates slide apart from each other (examples of which can be seen at mid-ocean ridges and active zones of riftingg. When two plates move apart from each other and the space that this creates is filled with new crustal material sourced from molten magma that forms below. The origin of