AST 251 Lecture 7

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Astronomy & Astrophysics

AST251 Lecture 7How did it start o The essential organic materials CO CH water H N were there 2422o Comets and meteorites may have brought more complex organic molecules from outer space and water o Steps neededFormation of organic molecules amino acids and nucleotidesJoining of large molecules into proteins and nucleic acidsAggregation into droplets with different chemical properties than the environmentReplication and heredityRNA and DNAThe early atmosphere o It did not contain oxygen and was dominated by hydrogen compounds o Volcanic gasescarbon dioxide about 351000x more than todays nitrogen hydrogen sulfide steam methane o Red or orange in colour thick and opaquelike Venus o Heat deposited by frequent hits by comets and meteorsSome hits vaporized the oceans but some brought water ice from the outer solar system o Rapid changes of solar illuminationearly Sun more variable and 30 fainter than today o Rapid rotation of the globe812hand violent lightning stormsEartha water planet o Ocean crust sinks back into mantle o Continental crust floats on top and grows over time o The total amount of water on Earth is 01 of its massCompare with outer solar system20 o Height variation of surface 8km above 5km below the sea levelAverage ocean depth 4kmWith twice the water 02 of mass oceans would cover all the landThe MillerUrey experiment o 1920s a realization that the early atmosphere was without any oxygeno 50s Miller and Urey performed an experiment of electrical discharges in an atmosphere of water vapour methane ammonia and hydrogen o After 1 week it produced many amino acids among 18 produced 6 occur in living organismsEarly ideas about the origins of Life o Pungent ponds of tidal water full of stuffVulnerable to UV radiation no oxygen hence no ozone layerVulnerable to impacts
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