Lecture 5: Timescale of Earth History

  • Age of the sun and solar system
  • ~4.57 Billion years old (Giga Annums)
  • Based on models of stellar evolution and dating of primitive solar system objects
  • Age of earth: ~4.54 Ga
  • Based on ages of terrestrial rocks + age of solar system + models of solar system formation

Nebular Hypothesis Explains the Origin of the Solar System

  • Interstellar cloud of gas and dust
  • Rotating gently
  • One part of the cloud began to get denser and began a gravitational collapse
  • Solar nebula is formed
  • We now have a nebula with a center that is collapsing in itself and it formed into a flat disc highest temp and highest pressure in the center
  • When the temp and pressure gets high enough, nuclear fusion begins and a sun is born

Accretion - building up by individual particles sticking together

Summary of Steps

  • Interstellar cloud of gas and dust
  • Rotating, flattened disc
  • Pressure and temp gradient
  • Nuclear fusion in the sun
  • Condensation of materials/dust
  • Accretion of objects
  • Differentiation (different material segregate from each other)

Early Earth

  • Very hostile to life
  • Constant volcanic activity
  • Meteorite impact bombardment
  • Intense UV radiation from the sun
  • No "free" oxygen in the atmosphere
  • No liquid water

Water Molecules Have Characteristics That Make it Crucial For Life

  • They are polar
  • Liquid over a wide range of temps
  • Strong cohesion (transports chemicals)
  • High heat capacity
  • Transparent to light
  • Solid form is less dense liquid

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