Earth's Layered Structure: Core, Mantle, Crust and More

The Earth is divided into three main layers The dense, hot inner core (yellow), the molten outer core (orange), Core, mantle & Crust the mantle (red), and the thin crust (brown)e in the known universe.

Interior of E arth

Interior of E arth 1. continental crust 2. Oceanic crust 3. U pper m antle 4. L ow er m antle 5. Outer core 6. Inner core A :M ohorovi i discontinuity B :G utenberg D iscontinuity C :L ehm ann B ullen discontinuity.

The structure of E arth can be defined in tw o w ays M echanically, it can be divided intolithosphere,asthenosphere,m esospheric m antle,outer core, and theinner core. C hem ically, E arth can be divided into the crust, upper m antle, low er m antle, outer core, and inner core. The geologic com ponent layers of E arth are at the follow ing depths below the surface

D epth (km ) C hem ical layer D epth (km ) M echanical layer D epth (km ) PRE M[4] 0 80* L ithosphere 0 80* L ithosphere 0 35 C rust 0 10 10 20 20 80 U pper crust L ow er crust L ID 35 670 U pper m antle 80 220 A sthenosphere M esospheric m antle A sthenosphere 220 2,890 220 410 400 600 Transition zone 600 670 Transition zone L ow er m antle U pperm ost M id-low er ... D layer Outer core Inner core 670 2,890 L ow er m antle 670 770 770 2,740 2,740 2,890 2,890 5,150 5,150 6,370 2,890 5,150 5,150 6,370 *D epth varies locally betw een 5 and 200 km . D epth varies locally betw een 5 and 70 km . Outer core Inner core 2,890 5,150 5,150 6,370 Outer core Inner core

Crust R anges from 5 70 kilom etres (3.1 43.5m i)in depth and is the outerm ost layer. The thin parts are theoceanic crust, w hich underlie the ocean basins (5 10km ) and are com posed of dense (m afic) iron m agnesiumsilicateigneous rocks, likebasalt. The thicker crust is continental crust, w hich is less dense and com posed of (felsic)sodiumpotassiumalum iniumsilicate rocks, likegranite. The crust-m antle boundary occurs as tw o physically different events. First, there is a discontinuity in theseism icvelocity, w hich is m ost com m only know n as theM ohorovi i discontinuityor M oho. The cause of the M oho is thought to be a change in rock com position from rocks containingplagioclase feldspar(above) to rocks that contain no feldspars (below ). Second, in oceanic crust, there is achem icaldiscontinuity betw eenultram aficcum ulates and tectonizedharzburgites, w hich has been observed from deep parts of the oceanic crust that have beenabductedonto the continental crust and preserved asophiolite sequences.

Mantle E arth's m antleextends to a depth of 2,890km , m aking it the planet's thickest layer. The m antle is divided intoupperandlow er m antleseparated by atransition zone. Thepressureat the bottom of the m antle is 140 G P a(1.4 M atm ). The m antle is com posed ofsilicaterocks richer in iron and m agnesium than the overlying crust. A lthough solid, the m antle's extrem ely hot silicate m aterial can flow over very long tim escales. C onvectionof the m antle propels them otion of the tectonic platesin the crust. Thesource of heatthat drives this m otion is the prim ordial heat left over from the planet's form ation renew ed by the radioactive decay of uranium ,thorium , andpotassiumin E arth's crust and m antle. D ue to increasing pressure deeper in the m antle, the low er part flow s less easily, though chem ical changes w ithin the m antle m ay also be im portant.

Core The average density of E arth is5.515 g/cm 3. B ecause the average density of surface m aterial is only around3.0g/cm 3 Seism ic m easurem ents show that the core is divided into tw o parts, a "solid" inner core w ith aradiusof 1,220km [and a liquid outer core extending beyond it to a radius of 3,400km . The densities are betw een 9,900 and 12,200 kg/m 3 in the outer core and 12,600 13,000kg/m 3in the inner core. The core is thus believed to largely be com posed of iron (80%), along w ithnickeland one or m ore light elem ents, w hereas other dense elem ents, such asleadanduranium , either are too rare to be significant or tend to bind to lighter elem ents and thus rem ain in the crust (seefelsic m aterials). Som e have argued that the inner core m ay be in the form of a single ironcrystal. The liquid outer core surrounds the inner core and is believed to be com posed of iron m ixed w ith nickel and trace am ounts of lighter elem ents. Som e have speculated that the innerm ost part of the core is enriched ingold,platinumand othersiderophile elem ents.