What are tectonic plates and why do they move?

Answer 1

Tectonic plates are segments of the Earth's lithosphere, the hard rocky outer shell composed of the crust and the uppermost mantle. This shell is divided by lines of faults, ridges of plate creation, and zones of plate destruction. All in all, there are roughly 30 tectonic plates which cover the entire surface of the planet. Plates can be composed of oceanic crust, continental crust, or a combination of both.

The movement of the plates is caused by the convection currents of heat from the Earth's interior. This heat, rising toward the surface through the mantle causes movement of plastic like rock in the asthenosphere, the layer of Earth directly below the lithosphere. At thinner areas of the crust, such as the mid-ocean ridges, this plastic rock undergoes a transformation, or phase change, into a liquid due to the decrease of lithostatic pressure. The molten rock rises and eventually cools, forming new crust.

At the other end of the convection current, older, cooler oceanic crust is being subducted under less dense crust, falling back into the mantle. The Earth's plates are riding on top of the currents caused by these processes.

The main features of plate tectonics are:

• The Earth's surface is covered by a series of crustal plates.
• The plates are composed of crustal rock and solid upper mantle which is called the lithosphere. * Plates are composed of continental and oceanic crust.
• The oceanic crusts are continually moving, spreading from the center, sinking at the edges, in a process of recycling.
• Rising legs of convection currents beneath the plates create additional plate material at mid-ocean ridges, sinking legs of convection currents swallow old crustal plates at subduction zones.
• The heat driving the convection currents is from radioactive decay of material within the Earth and from residual heat from accretion processes during Earth's formation.

Answer 2

The tectonic (or lithospheric) plates are composed of the rocky crust and outermost rocky layer of the mantle which are fused together. The entire outer surface of the planet is divided into these plate formations, roughly 30 in total, which vary in size from over 100,000,000 square miles (Pacific Plate) to the Galapagos microplate at 12,000 square miles. The individual plates are separated by fault lines which extend from the surface all the way to the asthenosphere, at which point the fault disappears due to the plasticity of the rock that exists there. The plates are constantly in relative motion to each other, but this motion is extremely slow due to the incredible amount of mass being moved. The boundaries between plates can be convergent (where they are colliding from opposite directions), divergent (where they are moving away from each other), or transform (where they are grinding past each other). Due to differences in density between oceanic and continental lithospheres, collisions will either result in subduction, where the denser plate dives beneath the less dense plate, and flows to be remelted into the asthenosphere, or in mountain building, where neither plate subducts but is thrust upward. This happens in continental to continental lithospheric plate collision. At divergent plate boundaries, the lithosphere is hot and thin and the fault between plates acts as a conduit for heated rock to reach the surface where it forms into new crust. The bulk of divergent boundaries are under the oceans, forming the mid-ocean ridge system, the world's longest continuous mountain range. At transform boundaries, the plates grind past each other (ex: San Andreas Fault), and can result in earthquakes as the grinding rocks suddenly snap into new positions. Plate movements occur because the layer of Earth directly below the lithosphere, the asthenosphere, is hot enough, and under enough lithostatic pressure to prevent its melting, that it can deform without fracture. Currents of heat from the Earth's interior rise to this layer and form convection currents that slowly move this plastic layer of rock. The hard lithosphere is thus moved in a conveyor belt like fashion by the convection current in the asthenosphere. The energy driving all of these processes is heat from the interior of the Earth derived from radioactive decay and residual heat from Earth's formation, and the insulating effects of Earth's mass.

Answer 3

tectonic plates are the rocky seagments in earths lithosphere.