Earth layers {planet layer} are core, mantle, and crust.
Earth center {core, Earth} {Earth core} has been the same since 3,500,000,000 years ago, after heating and layering ceased.
Earth center {inner core, Earth} is solid iron with some nickel and cobalt. Inner core has pressure 20,000 tons/in^2, temperature 4000 F to 8000 F, and radius 800 miles.
Layer {F shell} above inner core is 300 miles thick.
Layer {outer core} above F shell is liquid iron with some nickel, cobalt, silicon, and sulfur. Outer core has pressure 10,000 tons/in^2 and is 1375 miles thick.
Layer {D shell} above outer core is several hundred miles thick.
Above core D shell is layer {mantle, Earth}|. Mantle is 1800 miles thick and contains 80% of Earth volume.
temperature
Mantle temperature at 500,000 meters deep is 2300 K. Mantle temperature at 100,000 meters deep is 1500 K. Temperature increases with depth, 1 C every 30 meters. Lower mantle, below 700,000 meters deep, has convection currents caused by heat.
density
Below 650,000 meters deep, density is 5.5 g/cm^3. Between 400,000 to 650,000 meters deep, density is 4.5 g/cm^3. Above 400,000 meters deep, density is 3.5 g/cm^3. In upper mantle, which is 50 miles thick, density is 2.6 g/cm^3.
rock types
Lower mantle has dunite, which is mostly olivine, with some peridotite. Olivine has magnesium, silicon, and oxygen. Upper mantle has serpentine, at 50 miles to 100 miles above olivine, where 0.1% water and some carbon dioxide change olivine and pyroxene into serpentine and hydrogen {serpentinization}.
Iron and magnesium silicate olivines are 100,000 meters to 250,000 meters deep, in lower upper mantle {asthenosphere}.
Iron and magnesium silicates {dunite} are mostly olivine and make lighter-color veins in upper mantle.
Iron and magnesium silicates {eclogite} are in mantle.
Above Mohorovicic discontinuity is surface layer {crust}|.
Layer {Mohorovicic discontinuity} above mantle is thin.
Upper-mantle serpentine layer and lower-crust sial layer make layer {lithosphere}.
Lower crust is a three-mile thick heavy iron-and-magnesium-silicate basalt layer {sial layer}. Basalt forms from melted upper-mantle serpentine under lower pressure. Basalt crust density is 2.3 g/cm^3.
Upper crust has landmasses {continent, land}|. Continents now cover 25% of Earth surface. Continents average 20 miles thick and can be 40 miles thick. True continent edge is below ocean at continental-shelf edge, up to 400 miles from shore.
rocks
Continental rock is permanent, with no recycling back into crust or mantle. Continents are mostly granite, with density 2.1 g/cm^3 {sima layer}, so they rise above seas.
formation
First continent rocks appeared 4,000,000,000 years ago, as continents grew from upper mantle. After first continent-formation period ended 3,500,000,000 to 3,800,000,000 years ago, continents were 5% to 10% of crust. First-formation-period rocks are in Isua in southwest Greenland. These rocks have greenstone belts, granite-gneiss terrains, or igneous rocks cutting through them from upper mantle. Greenstone belts contain ultramafic rock and mafic rock, as xenolith.
Second continent-formation period, from 2,600,000,000 to 2,900,000,000 years ago, formed 50% to 60% of continental Archean rock.
Third continent-formation period was 1,700,000,000 to 1,900,000,000 years ago.
Fourth continent-formation period was 900,000,000 to 1,100,000,000 years ago.
Fifth continent-formation period was 600,000,000 years ago.
Igneous rock {mafic rock} can be mostly iron and magnesium. Mantle basalt, ocean-floor bedrock, and lava are mafic.
Greenstone belts contain volcanic rock {ultramafic rock} and partially melted mafic rock, which have no water.
Greenstone belts contain ultramafic and mafic rock, which have no water {xenolith}.
The second continent formation period, from 2,600,000,000 to 2,900,000,000 years ago, formed 50% to 60% of continents {Archean rock}.
Continent has independent masses {subcontinent} that have come together by plate movement.
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Date Modified: 2022.0225