Comets and the Origin and Evolution of Life
Comets and the Origin and Evolution of Life
Comets and the Origin and Evolution of Life
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Contents XIII<br />
4.4 Observations from Massive Star-Forming Regions . . . . . . . . . . . . . . . 122<br />
4.4.1 Current Research on Macromolecules<br />
in HMCs <strong>and</strong> <strong>Comets</strong> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124<br />
4.4.2 Sgr B2(N-LMH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125<br />
4.4.3 O<strong>the</strong>r Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127<br />
4.4.4 <strong>Comets</strong> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129<br />
4.5 Summary <strong>and</strong> Prognosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130<br />
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131<br />
5 Impact Delivery <strong>of</strong> Prebiotic Organic Matter to Planetary<br />
Surfaces<br />
E. Pierazzo, C.F. Chyba ..........................................137<br />
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138<br />
5.2 Sources<strong>of</strong>OrganicMaterial ..................................138<br />
5.3 Hydrocode Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142<br />
5.4 Earth:SignificantDelivery ...................................145<br />
5.5 Mars:BalancingFactors .....................................150<br />
5.6 Europa:ImpactorLoss ......................................155<br />
5.7 Amino Acids on <strong>the</strong> Moon: Impact Delivery? . . . . . . . . . . . . . . . . . . . 160<br />
5.8 Summary <strong>and</strong> Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161<br />
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162<br />
6 <strong>Comets</strong> <strong>and</strong> Prebiotic Organic Molecules on Early Earth<br />
C.F. Chyba, K.P. H<strong>and</strong> ...........................................169<br />
6.1 The Uninhabitable Habitable Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169<br />
6.1.1 The Habitable Zone <strong>and</strong> Liquid Water . . . . . . . . . . . . . . . . . . 170<br />
6.1.2 Are <strong>the</strong> Earth’s Oceans Extraterrestrial? . . . . . . . . . . . . . . . . 171<br />
6.1.3 D/H Ratios <strong>and</strong> Noble Gas Evidence . . . . . . . . . . . . . . . . . . . 172<br />
6.2 The Time Window for <strong>the</strong> <strong>Origin</strong> <strong>of</strong> <strong>Life</strong> . . . . . . . . . . . . . . . . . . . . . . . 173<br />
6.2.1 Frustration <strong>of</strong> <strong>the</strong> <strong>Origin</strong> <strong>of</strong> <strong>Life</strong> . . . . . . . . . . . . . . . . . . . . . . . . 174<br />
6.2.2 Micr<strong>of</strong>ossils <strong>and</strong> Stromatolites . . . . . . . . . . . . . . . . . . . . . . . . . . 174<br />
6.2.3 Molecular Biomarkers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175<br />
6.2.4 Carbon Isotope Fractionation . . . . . . . . . . . . . . . . . . . . . . . . . . 176<br />
6.3 Endogenous Production <strong>of</strong> Prebiotic Organic Molecules . . . . . . . . . . 177<br />
6.3.1 Nature <strong>of</strong> <strong>the</strong> Early Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . 177<br />
6.3.2 Energy Sources <strong>and</strong> Atmospheric Organic Production . . . . . 179<br />
6.3.3 Organic Production at Hydro<strong>the</strong>rmal Vents . . . . . . . . . . . . . . 182<br />
6.4 TheLunarCrateringRecord .................................182<br />
6.4.1 A Terminal Lunar Cataclysm? . . . . . . . . . . . . . . . . . . . . . . . . . 183<br />
6.4.2 Implications for <strong>the</strong> Mass Flux on Early Earth . . . . . . . . . . . 185<br />
6.5 Impact Delivery <strong>of</strong> Intact Exogenous Organics . . . . . . . . . . . . . . . . . . 186<br />
6.5.1 Interplanetary Dust Particles <strong>and</strong> Micrometeorites . . . . . . . . 187<br />
6.5.2 Interstellar Dust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189<br />
6.5.3 Meteorites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189<br />
6.5.4 Catastrophic Airbursts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190<br />
6.5.5 Big Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190