Uhh...Plate Tectonics?

Plate tectonics explains the massive movement of Earth's lithosphere. The outermost part of the Earth is divided into to parts. Above is the lithosphere, being comprised of the crust and the rigid upper part of the mantle. Below the lithosphere lies the asthenosphere. Although the asthenosphere is solid, it has low viscosity and shear strength. It can flow like a liquid on the geological time scales. The deeper mantle below the asthenosphere is more rigid due to the higher pressure.

The Lithosphere is separated into what we call tectonic plates. On the Earth, there are seven major and the rest are minor. The lithospheric plates move on the asthenosphere. The tectonic plates can consist of continental crust or oceanic crust, usually only one single plate carries them both. Each plate meets another plate at a plate boundary.The way the plates move is in relation to each other in three types of plate boundaries. The three are convergent or collision boundaries, divergent or spreading boundaries, and transform boundaries.

• Transform boundaries-occurs where plates slide, or grind past each other along transform faults.

• Divergent boundaries-occurs where two plates slide apart from each other.

• Convergent boundaries-occurs where two plates slide towards each other forming either a subduction zone or a continental collision.

• Tectonic plates are able to move because of the relative density of oceanic lithosphere and the relative weakness of the asthenosphere. Dissipation of heat from the mantle is acknowledged to be the original source of energy driving plate tectonics. The current view, although it is still a matter of some debate, is that excess density of the oceanic lithosphere sinking in subduction zones is the most powerful source of plate motion.

When it forms at mid-ocean ridges, the oceanic lithosphere is initially less dense than the underlying asthenosphere, but it becomes more dense with age, as it conductively cools and thickens.

The greater density of old lithosphere relative to the underlying asthenosphere allows it to sink into the deep mantle at subduction zones, providing most of the driving force for plate motions. The weakness of the asthenosphere allows the tectonic plates to move easily towards a subduction zone. Although subduction is believed to be the strongest force driving plate motions, it cannot be the only force since there are plates such as the North American Plate which are moving, yet are nowhere being subducted. The same is true for the enormous Eurasian Plate. The sources of plate motion are a matter of intensive research and discussion among earth scientists.


With great pleasure,
Aaron