Earths Crust: outermost shell of a terrestrial planet
Crust
Earths crust The crust is the outermost layer of Earth.
Earth’s Crust
For upon |“Crust” describes the outermost shell of a terrestrial planet. Earth’s crust is generally divided into older, thicker continental crust and younger, denser oceanic crust. The dynamic geology of Earth’s crust is informed by plate tectonics.
Earth’s Size
The brittle crust is just one of Earth’s three major layers. The thin, 40-kilometer (25-mile) deep crust—just 1% of Earth’s mass—contains all known life in the universe.
Earth’s Chemicals
The most abundant chemicals in Earth’s crust are silicates—minerals with high silicon and oxygen levels.
Earth’s Movement
Islands, ocean trenches, volcanoes, and mid-ocean ridges are all formed by the movement of molten material between the Earth’s mantle and crust.
A More Complicated Look
Oceanic Crust
The oceanic crust is constantly formed by seafloor spreading at mid-ocean ridges, where tectonic plates are tearing apart from each other. The age and density of oceanic crust increase from sites of seafloor spreading.
Pillow Lava
The rocks of the oceanic crust are nicknamed “sima” for their most characteristic elements (silicon and magnesium). Basalts, like this pillow lava near the Galapagos Islands, are the most abundant sima rocks.
Mariana Trench
Just as the oceanic crust is formed at mid-ocean ridges, it is destroyed in subduction zones. As oceanic crust sinks into the mantle, and maybe ultimately “recycled” as it surfaces again as crust-making lava at mid-ocean ridges and volcanoes. Largely due to subduction, oceanic crust is much, much younger than continental crust.
Ophiolite
Oceanic crust is often studied through ophiolites, remnants of oceanic crust forced above sea level by tectonic activity. This pillow lava, formed by tectonic activity on the seafloor billions of years ago, is now a part of the French Alps.
Continental Crust
The oceanic crust is created by divergent plate boundaries. Continental crust is created by convergent plate boundaries, where plates crash into each other. The crustal movement here is often associated with orogeny, the process of mountain-building. The massive Himalayas and Andes mountain ranges are the thickest and oldest parts of our continental crust.
Granite
The rocks of continental crust are nicknamed “sial,” after their most characteristic elements (silicon and aluminum). Granites, like these sheets in Yosemite National Park, California, are the most abundant seal rocks.
Tvashtar
All terrestrial planets and moons have a crustal upper layer. The crusts of most planets and moons in our solar system lack tectonic activity and are much more brittle and rigid than Earth’s. Io, a moon of Jupiter, is an exception: Io is the most volcanically active celestial body in the solar system. This volcano, Tvashtar, is ejecting material 200 miles (322 kilometers) into Io’s atmosphere.
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