BIOL 102 Lecture 6: Chapter 25 Part 1
20 Nov 2016
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Past organisms were very diff from those now alive. Fossil record shows macroevolutionary changes over large time scales, for example: the emergence of terrestrial vertebrates. Impact of mass extinctions: origin of flight in birds. Conditions on early earth made the origin of life possible. Earth formed about 4. 6 billion yrs ago. Bombardment of earth by rocks and ice likely vaporized water and prevented seas from forming before about 4 billion yrs ago. Earth"s early atmosphere likely contained water vapor and chemicals released by volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen) In the 1920s, a. i oparin and j. b. s haldane hypothesized that the early atmosphere was a reducing enviro. In 1953, stanley miller and harold urey conducted lab experiments that showed that the abiotic synthesis of organic molecules in a reducing atmosphere is possible. But the evidence is not yet convincing that the early atmosphere was in fact reducing.
