Astronomy 2021A/B Study Guide - Midterm Guide: Tunguska Event, Martian Meteorite, Impact Crater
14 Mar 2014
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Chapter 6 the origin and evolution of life on earth. Stromatolites: living: colonies of bacteria living in outer layer of sedimentary rocks. Sediment mixed with microbes that use photosynthesis to gain energy. Those on bottom use organic compounds left as waste for energy: 3. 5 byr old rocks: almost identical layered structure. If we find a rock with fossil from 3. 5 billion years ago we know life was before that time. Microfossils: very rare, oldest microfossils are 3. 5 billion years old (life may have existed before this) Studies suggest life originated 3. 5 3. 0 billion years ago: reside in sedimentary rock. Isotopic evidence: carbon 12 atoms are common and carbon 13 are more rare (1/89, living organisms and fossils show less carbon-13 than inorganic material, some rocks older than 3. 85 byr show the low 13c abundance. Living fossils (living creatures) can show relationships: ex. Slow investigation: dna sequencing is slow and painful.
