Over millions of years, the mantle cooled. The molten material that surrounded the core was the early mantle. The heaviest material, mostly iron and nickel, sank to the center of the new planet and became its core. Crafting the Crust Billions of years ago, the planetary blob that would become the Earth started out as a hot, viscous ball of rock. Near the Moho, the temperature of the crust ranges from 200° Celsius (392° Fahrenheit) to 400° Celsius (752° Fahrenheit). The upper crust withstands the ambient temperature of the atmosphere or ocean-hot in arid deserts and freezing in ocean trenches. Just as the depth of the crust varies, so does its temperature. ![]() Isostatic equilibrium depends on the density and thickness of the crust, and the dynamic forces at work in the mantle. Not all regions of Earth are balanced in isostatic equilibrium. Isostasy describes the physical, chemical, and mechanical differences between the mantle and crust that allow the crust to “float” on the more malleable mantle. The lithosphere’s depth varies, and the Mohorovicic discontinuity (the Moho)-the boundary between the mantle and crust-does not exist at a uniform depth. Earth’s layers constantly interact with each other, and the crust and upper portion of the mantle are part of a single geologic unit called the lithosphere. At the center of the Earth is a hot, dense metal core. Beneath the crust is the mantle, which is also mostly solid rocks and minerals, but punctuated by malleable areas of semi-solid magma. The crust is made of solid rocks and minerals. ![]() Earth has three layers: the crust, the mantle, and the core. ![]() Our planet’s thin, 40-kilometer (25-mile) deep crust-just 1% of Earth’s mass-contains all known life in the universe. “ Crust” describes the outermost shell of a terrestrial planet.
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