BIOL 1020H Lecture Notes - Lecture 1: Paleozoic, Cellular Respiration, Lightning
Document Summary
Past organisms were very different from those now alive. The fossil record shows macroevolutionary changes over large time scales, for example: the emergence of terrestrial vertebrates, the impact of mass extinctions, the origin of flight in birds. The earth formed about 4. 6 billion years ago. No life could have existed for the first 2-3 million years as collisions from comets from space would have bombarded the earth creating far too much heat. The first atmosphere was mostly water vapour and carbon dioxide that, as earth cooled, condensed into oceans and escaped into space. In the 1920"s, a. i. oparin and j. B. s. haldane hypothesized that the early atmosphere was a reducing environment: energy came from lightning and intense uv radiation. In 1953 stanley miller and harold urey conducted lab experiments that showed that the abiotic synthesis of organic molecules including amino acids, in a reducing atmosphere was possible. However, early atmosphere may not have been reducing.
