adminPlate tectonics is the scientific theory that attempts to explain the movements of the Earth’s lithosphere that have formed the landscape features we see across the globe today. By definition the word “plate” in geologic terms means a large slab of solid rock.“Tectonics” is a part of the Greek root for “to build” and together the terms define how the Earth’s surface is built up of moving plates.
The theory of plate tectonics itself says that the Earth’s lithosphere is made up of individual plates that are broken down into over a dozen large and small pieces of solid rock.
These fragmented plates ride next to each other on top of the Earth’s more fluid lower mantle to create different types of plate boundaries that have shaped the Earth’s landscape over millions of years.
A tectonic plate itself is defined as a rigid segment of the Earth’s lithosphere that moves separately from those surrounding it.
There are seven major plates (North America, South America, Eurasia, Africa, Indo-Australian, Pacific and Antarctica) as well as many smaller microplates such as the Juan de Fuca plate near the United States’ state of Washington ( See map of plates below).
There are three main driving forces for the movement of the Earth’s tectonic plates.
They are mantle convection, gravity and the Earth’s rotation.
Mantle convection is the most widely studied method of tectonic plate movement.
There are large convection currents of molten material in the Earth’s upper mantle.
As these currents transmit energy to the Earth’s asthenosphere (the fluid portion of the Earth’s lower mantle below the lithosphere) new lithospheric material is pushed up toward the Earth’s crust.
Evidence of this is shown at mid-ocean ridges where younger land is pushed up through the ridge, causing the older land to move out and away from the ridge, thus moving the tectonic plates.
Gravity is a secondary driving force for the movement of the Earth’s tectonic plates. At mid-ocean ridges the elevation is higher than the surrounding ocean floor.
As the convection currents within the Earth cause new lithospheric material to rise and spread away from the ridge, gravity causes the older material to sink toward the ocean floor and aid in the movement of the plates.
The Earth’s rotation is the final mechanism for the movement of the Earth’s plates but it is minor in comparison to mantle convection and gravity.
As the Earth’s tectonic plates move, they interact in a number of different ways and they form different types of plate boundaries.
Divergent boundaries are where the plates move away from each other and new crust is created. Mid-ocean ridges are an example of divergent boundaries.
Convergent boundaries are where the plates collide with one another causing the subduction of one plate beneath the other.
Transform boundaries are the final type of plate boundary and at these locations no new crust is created and none is destroyed.
Instead the plates slide horizontally past one another. No matter the type of boundary though, the movement of the Earth’s tectonic plates is essential in the formation of the various landscape features we see across the globe today. — geography.about.com
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