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Unformatted text preview: 1 Extraterrestrial Life: Spring 2008 When did critical events in the evolution of life on Earth occur? Most dates more than about 1 billion years ago are based on indirect evidence - can be disputed… • prokaryotes • eukaryotes • multicellular organisms • intelligent life Extraterrestrial Life: Spring 2008 Prokaryotes Single celled organisms (bacteria and archaea) that lack cell nucleus and other `organization ’ within the cell Isotopic evidence + rock beds called stromatolites suggest that the simplest life may have started 3.5 - 3.8 billion years ago About the time the Late Heavy Bombardment on the Moon ended Extraterrestrial Life: Spring 2008 Prokaryotes have much more diverse metabolic pathways than more complex organisms • anaerobic- do not require oxygen… necessary since the early atmosphere was oxygen poor • can derive energy from reactions involving heat, inorganic materials such as hydrogen, sulphur etc • photosynthesis probably developed early, but did not initially use water and did not yield oxygen as a byproduct Extraterrestrial Life: Spring 2008 Eukaryotes Single or multicellular organisms that have cell nuclei...
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This note was uploaded on 08/31/2009 for the course GEOL 3300 taught by Professor Staff during the Spring '08 term at Colorado.
- Spring '08