A map of Earth's tectonic plates. Plate boundaries are shown in red. Learn more about the geologic features related to Earth's tectonic plates at This Dynamic Planet
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Modified from USGS
Many forces cause the surface of the Earth to change over time. However, the largest force that changes our planetís surface is the movement of Earth's outer layer through the process of plate tectonics. This process causes mountains to push higher and oceans to grow wider.
As shown in this diagram, the rigid outer layer of the Earth, called the lithosphere, is made of plates which fit together like a jigsaw puzzle. These solid but lightweight plates seem to "float" on top of a more dense, fluid layer underneath.
Motions deep within the Earth carry heat from the hot interior to the cooler surface. These motions of material under the Earth's surface cause the plates to move very slowly across the surface of the Earth, at a rate of about 2 inches per year. There are several different hypotheses to explain exactly how these motions allow plates to move.
Interesting things happen at the edges of plates. Subduction zones form when plates crash into each other, spreading ridges form when plates pull away from each other, and large faults form when plates slide past each other.
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