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, & 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
  • COMPOSITIONAL STRUCTURE OF THE EARTH

  • STRENGTH STRUCTURE OF THE EARTH
  • Core - solid inner core & fluid outer core

    • Mantle & crust (see below)

    HADEAN EVOLUTION OF THE EARTH (No record on Earth)

  • FORMATION OF MOON - Mars-size body impacted newly-differentiated Earth
  • EARLY PLATE TECTONICS - MAFIC & ULTRAMAFIC CRUST INITIALLY; LATER ANDESITIC & GRANITIC CRUST generated by partial melting of mafic/ultramafic precursors
  • VOLATILES OUTGASSED TO FORM OCEANS & ATMOSPHERE (+ crust)
  • NH3 oxidized to Nitrogen to form 79% of atmosphere, H2O condensed into oceans, & CO2 scrubbed from atmosphere by reaction with H2O (& ultimately biologically fixed in the crust as limestone & coal)
  • atmospheric Oxygen (20%) is biogenic
  • EARLY ATMOSPHERE WAS ANAEROBIC
  • NO O2, NO OZONE (O3), LOTS OF ULTRAVIOLET RADIATION
  • atmospheric Argon (1%) is radiogenic

    • 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 diffence 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 are the compositional layers of the Earth?

    7. What are the strength layers of the Earth?

    8. What was the evolution of the Earth like during the Hadean?

    9. What is the evidence for these Hadean developments?

     

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