Tectonic plate (noun, Tek-TAHN-ick PLAYT)



Earths outermost layer, or lithosphere, is broken up into a giant jigsaw puzzle of tectonic plates. These huge slabs of rock hold both Earths continents and its seafloor. Theyre around 100 kilometers (miles) thick on average and include both Earths crust and upper mantle. Earth is covered in about a dozen main tectonic plates. And its the only planet known to have tectonic plates.



Explainer: Understanding plate tectonics



Earths tectonic plates continually slide around atop the hot, swirling rock beneath them. They move only a few centimeters per year. But over millions of years, those tiny movements add up. When tectonic plates bump into each other, they push up mountains. When plates slide beneath each other, they can form volcanoes. Plates can also slide past each other. Each of these movements can trigger earthquakes.



Even more dramatically, the shuffling of tectonic plates can give Earths surface a complete makeover. More than 200 million years ago, Earth had only one huge landmass: Pangaea. Over time, the shifting of tectonic plates broke that landmass apart and gave rise to the continents we see today.



In a sentence



A single catastrophic collision may have given Earth both its moon and its tectonic plates.



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