Origin of the Solar System & Evolution of the Earth

ORIGIN OF THE UNIVERSE

  • BIG BANG - 15-20 B.Y. AGO (RED SHIFT of optical spectra [EXPANDING Universe] & 3oK BACKGROUND TEMPERATURE [COOLING Universe])
  • composition has changed over time - only Hydrogen & Helium initially; heavier elements synthesized inside stars (released during supernovas)

    • NEBULAR-PROTOPLANET HYPOTHESIS - 4.6 B.Y. AGO (meteorite/moon ages)

  • ORIGINAL SOLAR NEBULA
  • abundant Volatiles (Hydrogen [H], Helium [He], water [H2O], ammonia [NH3], methane [CH4], carbon dioxide [CO2])
  • less abundant Refractory rock & metal grains
  • NEBULA DISTURBED(BY ADJACENT SUPERNOVA?)
  • contracts & flattens into a rotating solar disk (90% of mass in center)
  • protoplanets form at eddies by accretion of dust & gas into larger masses -> eventually form planets
  • REFRACTORY-RICH TERRESTRIAL PLANETS (MERCURY, VENUS, EARTH, MARS) FORM IN THE INNER PART OF SOLAR SYSTEM
  • temperatures were relatively hot
  • refractory rock & metal grains were solid
  • volatiles were gaseous
  • VOLATILE-RICH JOVIAN PLANETS (JUPITER, SATURN, URANUS, NEPTUNE) FORM IN THE OUTER SOLAR SYSTEM (BEYOND A POINT BETWEEN MARS & JUPITER)
  • temperatures were cold enough for volatile ices (particularly H2O, NH3, CH4) to form
  • accretion of significant amounts of volatile ices (plus refractory grains) to become massive enough to attract huge quantities of H & He
  • GREAT PRESSURES INSIDE the PROTO-SUN
  • temperatures hot enough (millions of degrees) for nuclear fusion to start
  • the Sun ignited
  • the solar wind started up & any volatile matter not accreted to a protoplanet was blown out of the solar system

    • DIFFERENTIATION OF THE EARTH

  • EARTH DIFFERENTIATED INTO COMPOSITIONAL & STRENGTH LAYERS
  • Hot, Heterogeneous Accretion - it formed that way during accretion
  • SOLAR DISK INITIALLY HOT -> ONLY METALLIC PARTICLES (with high melting temperatures) ACCRETED as the Earth's core
  • SOLAR DISK COOLED -> more ROCKY GRAINS (with lower melting temperatures) crystallized & were ACCRETED as the Earth's mantle
  • SOLAR DISK FINALLY COOLED ENOUGH -> VOLATILE ICES crystallized & were ACCRETED as the Earth's hydrosphere & atmosphere
  • Cold, Homogeneous Accretion - DIFFERENTIATION LATER DUE TO HEATING & PARTIAL MELTING (heat from accretionary impacts, pressure in the interior of the Earth, & decay of radioactive elements with short half lives)
  • iron melted out & gravitationally settled to form core
  • incompatible elements melted out & gravitationally rose to form a crust from a MAGMA OCEAN
  • VOLATILES WERE "OUTGASSED" TO FORM OCEAN & ATMOSPHERE (+ crust) through the action of mantle convection & plate tectonics
  • Recently, astronomeres have found that comets may have contributed much of the water forming the Earth's early ocean

    • HADEAN EVOLUTION OF THE EARTH (No record on Earth)

    Study Questions

    1. When is the Universe thought to have formed? the Solar System? What is the evidence for each?

    2. What are the differences between refractory & volatile constituents?

    3. What are the names of the refractory-rich & volatile-rich planets?

    4. How did the difference between refractory-rich & volatile-rich planets develop?

    5. What are the 2 ways in which the Earth is thought to have differentiated into Compositional & Strength layers?

    6. What was the evolution of the Earth like during the Hadean? How did the moon form?

    7. What is the evidence for these Hadean developments?

     

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