Earth's continents were once bound together.
The Earth is comprised of multiple layers: the crust, mantle, outer core and inner core. The outermost portion of the crust is called the lithosphere; the crust underneath that is called the asthenosphere. According to the theory of plate tectonics, the Earth's crust is made up of puzzle pieces that constantly act on each other; one hits the other, which crushes another and so on.
Convergent
The world is a big puzzle and those pieces are everywhere. Convergent boundaries are areas of the Earth's crust where one kind of continental plate is subducted, i.e., when two plates collide, the weaker of the pair sinks below the other -- those pieces are sent downward inside the earth. This process may happen at any number of different kinds of boundaries such as an oceanic-continental or oceanic-oceanic, for example. Oceanic-oceanic convergence creates ocean trenches and underwater volcanoes; oceanic-continental and continental-continental often make mountains.
Divergent
Divergent boundaries happen when various portions of the Earth's "puzzle pieces" pull apart. Magma from far beneath the Earth's crust is sent upward causing it to cool and harden. Some plate tectonic theories say the oceans were created this way -- the North American plate and the Eurasian plate diverged to create the Mid-Atlantic Ridge, which, not only runs right through Iceland, but has increased the country's land mass, as well. As the Mid-Atlantic Ridge divides it, it is believed that Iceland will eventually pull apart for good, however.
Transform
Transform boundaries occur when two plates simply pass by each other -- neither are subducted or crushed. This activity sometimes causes fault zones. Most commonly found at the bottom of the ocean, transform boundaries are thought to essentially temper the activity generated by other plate boundary activity; divergent or convergent boundaries that create hot springs or volcanoes, for example. The San Andreas fault is a transform boundary that exists between both the North American and Pacific continental plates.
Plate Boundary Zones
Plate boundary zones, also known as conservative boundaries, are generally found along and between ocean and continental pieces often called belts. These types of boundaries have one defining characteristic that makes them different from other kinds of boundaries: they contain two larger plates and a collection of microplates, which are smaller pieces of crust material that do not get subducted or destroyed. The Mediterranean Alpine, North American and African plates, i.e., the areas around Spain, Morocco and Indonesia, are an example of plate boundary zones.
Tags: Earth crust, North American, boundary zones, each other, kinds boundaries
