Formation of layered earth homogenous earth after

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Formation of layered Earth - Homogenous earth after accretion - Earth heats up due to late large impacts - Heat causes melting and softening - Denser (iron and nickel) material sinks to center - forms core
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- Lighter material rises to the surface - forms crust - Process is called differentiation - Density = mass/volume - Compositional layers - Crust (0-70 km) density = 2.7 - 3.0 g/cc - ——————moho——————- - Mantle (to 2900 km) density = 3.3-10 g/cc - Core (to 6371 km) density = 10 - 13 g/cc - Outer: liquid Fe-metal - Inner: solid Fe-metal - Formation and Evolution of the Atmosphere and Oceans - Present-day: - 78% Nitrogen - 21% Oxygen - 0.9% Argon - 0.03% Carbon Dioxide - Original atmosphere - Was solar nebula - Hydrogen, Helium, Methane, Ammonia, CO 2 - Clears away from inner solar system by strong solar wind from proto-sun - Little affect on later events - Beginnings of enduring atmosphere - Outgassing of gases trapped in Earth’s interior - Also, enormous amounts of volcanism from very hot early Earth - Rich in CO 2 , SO 2 , H 2 O vapor, and N 2 , but no O 2 - Photosynthesis by cyanobacteria (blue-green algae) began to release O2 into the at- mosphere - Stomatolites by 3 bya - Near present levels by 1.5 bya and ozone also - First oxygen combined with iron to make iron oxide (Fe2O3) and formed banded iron formations (BIFs) - The First Continents - Lower density material floated to top of the mantle - continued differentiation - Probably recycled continuously - none preserved - Gave way to plate tectonics within first couple billion years - unclear when - Continental Drift - Alfred Wegener - early 1900s - Continents move - all together around 200 Ma supercontinent
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- Wegener believed that the continents plowed through the oceans and that movement was re- lated to earth rotation and gravitational pull of the moon; ideas were widely criticized and opposed - New technology applied to exploring ocean basins - Better understanding of Earth’s interior - Revolution in 1960’s - More comprehensive version - plate tectonic theory - Now widely accepted - Layers - Lithos = stone - Asthenes = weak - Lithosphere: solid crust; solid outermost layer of the mantle - Asthenosphere: largely solid, but mobile layer of mantle under the lithosphere - Two types of crust - Oceanic - Density: about 3.0 - About 5.7 kn thick - Continental - Density: average about 2.8 - 25-70 km thick - Plates vary in size - Plates may be entirely oceanic, continental, or mixed - All continent-ocean boundaries NOT plate boundaries - Passive vs. active continental margins - Passive means the continental and oceanic crust move together - Plate boundaries may change (ex. plates may disappear or combine) - Earth surface elevations - Everything is in comparison to sea level - Thickness of most continental areas is 35-50 km - Thickness of most ocean basins is 5-7 km - Thickest continental crust is 70+ km and they are mountains - “the thickness of the crust correlates to the surface elevation directly” higher thickness, higher surface elevation - Isostasy - Lower density (about 2.8 g/cc) crust “floats” on higher density (about 3.3 g/cc) mantle - Surface elevation depends on crustal thickness and density differences between crust and
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