Anatomy of a Planet

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Anatomy of a Planet
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Origin of the Solar System

• Gravitational collapse of huge gas dust cloud
• Rotation around a central mass
• Disk shaped cloud
• Temperature variations segregated matter
• Small particles accreted into larger
  planetesimals, finally planets

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The Earth is a layered (differentiated)
body -chemistry -density -pressure -heat
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How do we know? Drilling -wells drilled into
Earth are mostly in the upper 7 km of the crust
Deepest well Russian well in northern Kola
Peninsula20 year effort to drill a 12 km hole.
Target depth was 15 km.Costs are more than 100
million
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Ordinary Chondritic Meteorite -composition of
asteroids and the early solar system
-pyroxene chondrule in thinsection
-chondrules
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Achondritic Meteorite -differentiated planetary
crust?
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Iron Meteorites -actually mixture of Fe and
Ni -planetary cores?
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Earths Internal Structure

• The solid Earth has a layered structure
• Layers defined by composition and physical
  properties
• Compositional layers
• crust - mantle - core
• Physical layers
• lithosphere - asthenosphere - mesosphere - outer
  core - inner core

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Compositional Layers

• Crust
• Continental crust
• Thicker than oceanic crust - up to 75 km
• Less dense - 2.7 g/cm3

• Oceanic crust
• Thinner than continental crust - about 8 km
• More dense - 3.0 g/cm3

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Compositional Layers

• Mantle
• Largest layer in the Earth
• 2900 km thick
• 82 by volume
• 68 by mass
• Composed of silicate rocks with abundant iron and
  magnesium
• Density ranges from 3.2 to 5 g/cm3
• Fragments found in some volcanic rocks

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Compositional Layers

• Core
• Central mass about 7000km in diameter
• Average density of 10.8 g/cm3
• 16 by volume, 32 of mass
• Indirect evidence of composition
• Metallic iron

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Physical Layers

• Outer Core
• 2270 km thick
• Liquid, flows
• Flow creates magnetic field
• Inner Core
• 1200 km thick
• Solid

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Dr. Inge Lehmann (1888-1993) -discoverer of the
Earth's inner core. -Danish seismologist -discov
ered the P discontinuity P-wave deflections at
inner-outer core boundary
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Seismic Structure of the Earth

• Seismic wave velocities vary with depth
• Variation with depth is not regular
• Discontinuities exist at certain depths
• Represent discrete changes in the layered Earth
  structure

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Refraction waves passing from material of one
density to a material with a different density
change pathway bent.
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Outermost Layers of the Solid Earth
Low velocity zone -partially molten?
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Laboratory Experimentation
Piston-cylinder Apparatus -pressures up to 5 GPa
50,000X atmos pressure -workhouse for Upper
Mantle research
Piston-Cylinder 5 Gpa range
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The Multi-Anvil -pressures up to 50 GPa 500,000X
atmospheric -Lower Mantle Outer Core
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The Diamond Anvil -pressures up to 400 GPa -100
to 200 GPa commonly
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Schematic of the Diamond Anvil Cell