What is the internal structure of the Earth?
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formation of Earth
o formation of Earth from clumping of debris in early Solar System (movie)
o kinetic energy from impacts and heat from radioactive decay of short-lived
elements melted Earth (movie), allowing materials to differentiate (to separate
according to their density)
o differentiation causes heavy metals, such as iron and nickel, to settle in core,
while lightest silicates float to surface
o cause of differentiation is gravity
o without differentiation, all rocks would be one, uniform material
o result of differentiation was triple-layering of Earth due to gravity
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core of iron and nickel
mantle of dense rock
thin crust of lighter rock
how do we know about Earth's inner structure?
o drilling can only explore 10-15 km into crust
o
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seismic waves can probe 6400 km
 like light, waves bend according to density of rock
 after earthquake, seismologists can build a map of the internal structure
 find that density increases toward center
radioactive heating of core
o main source of heating inside the Earth
o heat is ultimate energy that drives geological activity on any planet
o atoms break down via radioactive decay, shooting subatomic particles and
photons outward ---> motions of neighboring atoms increase ---> temperature
rises
o reason why Newton and Buffon estimates were too short!