Earth has formed in our solar system

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Earth has formed in our solar system

• Chemistry of meteorites and sun provide
  constraints on the bulk composition of the Earth
• Geocentric view ? back in time (most of the
  course)
• ab initio view ? forward in time Evolutionary
  models)

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Planetary formation

• Collapse of an interstellar cloud (solar nebula)
  into a disc
• Formation of planetoids from condensation, then
  collision, drag, gravity

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All stars form from clouds of gas and dust which
roam our galaxy. Eventually, gravity causes the
cloud to collapse since the cloud is spinning,
material falls in along the "poles" faster than
it does near the "equator". This flattening
results in a disk-like object.
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Material slowly wends its way into the center of
this disk, forming a new star. While the star
continues to grow, lumps form in the disk which
will ultimately become planets.
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The disk eventually thins as more material falls
onto the star and the protoplanets. A hole in the
disk near the star forms as material is
completely incorporated into the star and
planets.
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Now fully formed planets exist within the hole,
even as new planets are still under construction
in the outer parts of the disk.
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Ultimately, the remaining dust clears completely,
leaving a fully formed solar system like our own.
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Constraints for planetary theory

• Planetary orbits nearly circular
• Bodes law
• Compositional classes

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Inner or terrestrial planets Small,dense, slow
rotation, few moons
Giant or jovian planets Large, low density, fast
rotation, numerous satellites
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Unknowns

• How dense was the solar nebula
• Time scales
• (fast ? homogeneous ? differentiation) (slow ?
  differentiated bodies)
• Temperature
• Gaz environment ? atmosphere

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Meteorites

• Offer the possibility to look back in time and
  deep into planets
• Stone and iron bodies that arrive on Earth in
  small numbers (mostly from asteroid belt)
• Most finds in Antarctica
• Classification

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• Meteorite Types Percentage that Falls to the
  Earth
• Stony meteorites
• Chondrites (85.7) (named after inclusion of
  chondrules)
• Carbonaceous
• Enstatite
• Achondrites (7.1)
• HED group
• SNC group
• Aubrites
• Ureilites
• Stony iron meteorites (1.5)
• Pallasites
• Mesosiderites
• Iron meteorites (5.7)