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ASTR/GEOL-2040: Search for life in the Universe: Lecture 6 • Delivery of C and H2O via comets & asteroids • Seeding of life Today • Delivery of water & carbon by comets • Panspermia (delivery of seeds for life) • Reading: – RGS pp. 23-34 – Lon pp. 383-384, 176, 112; 130-135 – BS pp. 121-127, 144-146 2 Enough carbon in inner parts? • [C]/[heavier] • Normalized Sun 1 • Earth: 30 Noticed in 1961 (J. Oro) RGS p.22 3 Puzzle • Not much Carbon where liquid water • A lot of carbon where water is frozen What is the reason? 4 Solar nebula • Wet: 5 Radial T gradient • From 1700 K to 20 K • Inner parts fewer volatile compounds • More refractories 6 How to define refractory? Refractory = resistant A. B. C. D. E. Solidifies at high temperature Melts at high temperature High Boiling temperature Evaporates at high temperature Condenses at high temperature 7 How to define refractory? A. B. C. D. E. Solidifies at high temperature Melts at high temperature High Boiling temperature Evaporates at high temperature Condenses at high temperature Liquid phase does not always exist 8 Phase diagram of water • From 1700 K to 20 K • Refractory minerals: T50>1100K 9 Earth: 1 atm = 1 hPa = 105 Pa, so its 1/1000 Table • From 1700 K to 20 K • Refractory minerals: T50>1100K 10 Carbon delivery (present rates) • Which type is the greatest C source? 11 Carbon delivery (present rates) 1.6 <0.001 2.6 • Which type is the greatest C source? – Crater-forming bodies – Arrive intermittently 12 Carbon delivery (present rates) 1.6 <0.001 2.6 0.32 • Greatest organic C source? • Compare with C of biomass: 6x1014 kg – 6x1014 kg / 0.3x106 kg/yr = 20 x 108 yr = 2Gyr Carbon delivery • Somewhat more anorganic than organic C – Organic C delivery continuous • Enough to produce all C in biomass – Early rates likely much higher; see moon 14 Also water is volative • Not much water during formation – temperatures too high dry accretion • Possible solution: – Late delivery from beyond ”snowline” – Evidence: depletion wrt meteorites • Low K/U (potassium to uranium ratio) – Indicator of relative depletion of volatiles 15 Is wet accretion possible? • Yes, by later inward migration – Need to look at orbital dynamics • Many body problem – Can easily become unstable 16 Nice model • Trial & error • Want low ecc’ty of gas giants • Wet Earth Late heavy bombardment • Nice model simulations • Find animation??? Gomes et al. (2005, Nature 435, 466) Late heavy bombardment • Nice model simulations • LHB theoretically possible Gomes et al. (2005, Nature 435, 466) Volatilized by impact? • Wet: volatilized by impact – If so: heavier isotopes enriched • Earth: no (66Zn depleted wrt 64Zn) – Moon: (66Zn enriched wrt 64Zn) – So Earth never got volatiles in the first place 20 Water on terrestrial planets • Not much on Venus and Mars – either acquired less than Earth, – or lost more • Earth: much is in the mantle (2-10 times) – Venus: unclear (losses by impact & sol wind) – Mars: loss by solar wind (MAVEN) 21 Alternative: late delivery • Also known as: late veneer – comets & asteroids – Formed beyond snow line • Potential problem D/H ~ 3x10-4 – Ocean water D/H = 1.56x10-4 • But 103P/Hartley 2 (IR): comp. w/ Earth • For the coma: core could be enriched 22 Different types of comets • From From ... Col to last 23 Panspermia • Arrhenius (1859-1927): spores survived • Lord Kelvin (1824-1907): via meteorites • Allan Hills meteorite (ALH 84001) – – – – – 4.5 Gyr: crystallized magma from Mars 4.0 Gyr: battered, but not ejected 3.6-1.8 Gyr: altered by water 1984: discovered in Antarctica 1996: NASA press conference 24 Why not Panspermia Earth Mars? A. Because of Earth’s atmosphere B. Because Earth is too massive C. Because Earth is closer to the Sun D. Because of either B or C E. Because of both B and C 25 Why not Panspermia Earth Mars? A. Because of Earth’s atmosphere B. Because Earth is too massive C. Because Earth is closer to the Sun D. Because of either B or C E. Because of both B and C 26 Panspermia • Not a hypothesis for origin of life – We could be related to Martian life (think) – Other way unlikely (against Sun, heavier) • Bacteria suspended animation – Virtually no metabolism (bact spores) – Hardy to heat, desiccation, radiation, chem. • Record so far 250 Myr (Lon 384) – Isolated bubbles, lake bed Salado in NM 27 How to tell apart? • How would you be able to tell whether we are Martians? • Discussion • This about special properties of our life 28 Radio(active) resistance • Arrhenius (1859-1927): spores survived 29 Radiation dose • • • • • 1 Gy (=Gray): SI unit for absorbed radiation 1 Gy = 1 J/kg (=100 rad) Biological effect (dep. nature of radiation) 1 Sv (Sieverts) = 1 Gy for el. mag. rad. = 10 Gy for fast neutrons, 20 for a particles Lon p. 386 30 Bacterial names • Deinococcus radiodurans – (D. Radiodurans) • Escherichia coli – (E. coli) 31 Position in classification scheme bacteria bacteria deinococcus-thermus proteobacteria deinococcales enterobacteriales deinococcaaceae enterobacteriaceae deinococcus escherichia radiodurans coli 32 Radiation dose • Deinococcus radiodurans • (D. Radiodurans) 33 Tardigrade • Get picture... 34 Next week’s material • Domains of life & extremophiles – Bacteria in antarctica survived -50 C (-58 F) – LUCA, the last common ancestor • RNA world – It can also act as catalyst – No proteins necessary 35 Preparation for quiz #1 • • • • • • • • Next week Thursday Check all lectures: def of life, order/disorder, Away from equilibrium Natural selection Carbon & Water, polar molecules Lipids and other building blocks Genetic code, A-T, G-C Biomarkers, meteorites, Miller/Urey, ... 36