Tectonic plates are large plates of rock that make up the foundation of the Earth's crust and the shape of the continents. They comprise the bottom of the crust and the top of the Earth's mantle. There are ten major plates on the Earth and many more minor ones. They float on a plastic-like part of the Earth's mantle called the asthenosphere and are most famously known for being the source of earthquakes.
Each tectonic plate is about 100 km (60 miles) in thickness with continental plates tending to be thicker than oceanic ones. The composure of the two varieties is also quite different. Oceanic plates consist of thicker basaltic rocks, compressed by the pressure of kilometers of water and contintental plates have a lower average density, containing granitic rocks with a heavy composition of aluminum and silica.
The mantle underneath the tectonic plates is constantly recirculating which causes them to float around slowly in a process called tectonic drift. This process was described well by the theory of plate tectonics, which solved several scientific dilemmas about the distribution of species when it was introduced. When plates push up against each other, they create mountain ranges and volcanoes and this is exactly how Mount Everest was created.
Over time, plate tectonics have caused the world's continents to be reshaped. Every continent was once part of an ancient supercontinent known as Pangaea and Antarctica was once located in a temperate climate. Marine fossils can be found on the peaks of the world's tallest mountains. The tectonic plates continue to move slowly, but it is unlikely that their movement will cause the world's face to change more rapidly than the growing technological influence of mankind. One day the plates' great momentum and pressure might even be used as a source of geological energy.
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