Layers of the Earth

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Notes: Layers of the Earth Crust Outer layer; covers the whole earth; varies in thickness from 5 to 60 Km. Together with the upper mantle, is part of a zone called the lithosphere. There are 2 kinds of crust: continental crust and oceanic crust. Continental Crust Exists under continents Average thickness is 30-50 Km (thickest under mountains), although it can be as thin as 10 Km in places Chemical composition: rocks rich in calcium and aluminum silicates **Note: a silicate contains the molecule, SiO2 Common rock types: granite and rhyolite Rocks are less dense, lighter in color than oceanic crust Oceanic Crust Exists under oceans Average thickness is 7 Km Chemical composition: rocks rich in iron and magnesium silicates Common rock types: basalt, obsidian, gabbro Rocks are more dense, darker in color than continental crust Mantle (Chemical Composition: iron & magnesium silicates) Lies underneath the crust 2900 Km thick The lithosphere is a zone made of the upper mantle and entire crust. It is made of cool, hard rock. Most (but not the very upper part) of the mantle is plastic rock: is both solid and molten at the same time. This zone is called the asthenosphere. Underneath the asthenosphere is the mesosphere, which is solid. The asthenosphere has convection currents, where matter rises to the top, cools, then comes back down again, in a continuous cycle. Core Center of the Earth; ~ 3500 Km thick Outer Core Made of molten iron and nickel 2270 Km thick Inner Core Made of solid iron and nickel. Is solid because of the extreme pressures it is under. 1220 Km thick As we progress from the exterior to the interior of the Earth: Temperature increases Pressure increases Density increases Chemical compsition changes Earth may be divided into 3 layers based on chemical composition Crust Mantle Core Earth may be divided into 5 layers based on physical properties Lithosphere Asthenosphere Mesosphere Outer core Inner core .

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