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GEOL 208 Lecture 1b

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GEOL 208 Lecture 1b

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  1. 0 Geology 208: The Earth, Moon and Planets • Today • Diary discussion • Origin, cont’d, chap. 15: 388-411 • Geology of the Earth: Skinner, chap 1: 17-20, 23-28; chap. 2: 33-61 • Next class (May the 14th) • cont’d, Geology of the Earth: Skinner, chap 1: 17-20, 23-28; chap. 2: 33-61 • Diary, letter of intent due “The Origin of the Solar System”

  2. c. The (post-Laplace) Solar Nebula Theory • Basis of modern theory of planet formation • planets form at the same time from the same cloud as star (sun) • therefore, planet origin not catastrophic • key is interstellar dust in solar nebula

  3. Condensation Hypothesis:formation & growth of planetessimals • Planet formation in nebula starts with growth of dust grains • …by condensation • - dust grains (around which atoms nucleate) are plentiful • form larger & larger balls (clumps) of matter (mass rises rapidly) 6/3/2014 3

  4. Condensation Hypothesis:formation & growth of planetessimals • …by accretion • as clumps grow larger (increasing surface area)… • sweep up new material • perhaps within ~100,000 yrs, objects hundreds of kilometres in diam. had formed • “planetesimals” “ protoplanets” 6/3/2014 6/3/2014 4 4

  5. Planetessimals-Protoplanets • planet type (rocky or gaseous), depends on temperature profile of solar nebula… • primitive solar system heated up with contraction & flattening • temp & density were highest at core/centre • several thousand degrees K at core / 100 K at Saturn (10AUs) Kelvin = Celsius + 273.15 00 Kelvin = absolute zero 00 C = 273.15 K

  6. Temperature Profile of Primitive Solar System (after condensation / just before accretion) • only metallic grains form around Mercury’s orbit • at 1 AU, rocky silicates form • at 3 /4 AUs water ice occurs • inner solar system • condensation from gas to solid began when temps fell to ~1000 K • outer solar system • lighter (lower density, i.e. H2O, CH4) gases in middle /outer regions • condense into solid form 6/3/2014 6

  7. Rock-Ice Dichotomy 6/3/2014 7

  8. Gas-Giant Formation Two Hypotheses 1. Core-acccretion hypothesis ------------- protoplanets, when large enough (mass-wise), could have captured gas from contracting nebula Four large protoplanets became cores of Jovian worlds But inconsistent with T Tauri phase, when intense (& early) stellar winds & radiation blow away most nebular gas

  9. Gas-Giant Formation Two Hypotheses 2. Gravitational instability ----------------- Giants form directly from nebula (skipped condensation and accretion stages) in outer, cool regions of the nebula 6/3/2014 9

  10. General Timeline of Solar-System Formation 6/3/2014 10

  11. General Timeline of Solar-System Formation

  12. Extrasolar Planets Modern theory of planet formation is evolutionary - many stars should have planets - …but extrasolar planets cannot be imaged directly, most of the time 6/3/2014 12

  13. Extrasolar Planets: direct detection • Brown dwarf star [2M1207 system] (mass insufficient to maintain “H” burning nuclear fusion) • planet (5x Jupiter mass) detected in infra-red, orbits 55 AU from star

  14. Extrasolar Planets: direct detection • Star HD 209458 • planet is 200 x 103 diam • transits every 3.5 days • blocks 2% of star’s light • V376 Pegasi • detection could occur if planet orbit lies in the plane of our line of sight • planet (partially) eclipses the star • if large enough, some decrease in luminosity could be observed

  15. Extrasolar Planets: indirect detection “red shift” - electromagnetic radiation emitted from object - (& detected by us), shifts to red end of spectrumas object (star) moves away from us 6/3/2014 15

  16. Earth: biography 16

  17. The Terrestrial Planets: common ground • Mercury, Venus, Earth & Mars (haves/have nots) a. solid surfaces: geology & geomorphology b. volcanism: surface change & climate c. impact cratering: surface age & lithology d. atmospheres: geomorphology, climate & life e. climate: geomorphology & life

  18. Earth: temporal & spatial scales Identifying the relevant “scales” of analysis is necessary to understand the origin & evolution of planetary environments 18

  19. Earth: history of geological activity Surface formations(visible today) have emerged only very recently (in geological time) 19

  20. 4 main stages of evolution 1 2 3 4 Earth formed 4.6 Gya from the inner solar-nebula Geological history of the Earth • Differentiation: 2 heat sources • decay of radioactive material (unstable nucleus loses energy) • potential energy of infalling material (meteorite /asteroid strikes) Most traces of bombardment (impact craters) destroyed by late geological activity 20

  21. core-temperature: 3000º- 5000ºC The Earth’s interior: the core Earth’s radius: 6400 km Core(radius): 3500 km (Fe, some nickel) inner - solid (high pressure) outer - liquid (low pressure) 6/3/2014 21 21

  22. Solid crust Solid mantle Liquid core Solid inner core The Earth’s interior Basic structure: melting point - temp. at which an element melts (transition from solid to liquid) - increases as pressure increases towards centre - inner core solid - Earth’s interior becomes hotter towards the center - core as hot as the sun’s surface 22

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