Astronomy 2021A/B Study Guide - Midterm Guide: Carbon-12, Stromatolite, Micropaleontology
3 Oct 2015
School
Department
Course
Professor
Document Summary
6. 1 searching for life"s origins: three lines of evidence that life began between 3. 85 byr and 3. 0 byr ago. Stromatolites, microfossils, isotopes of carbon: stromatolites rocks characterized by a distinctive layered structure. Example of a modern-day primitive colony of photoautotrophs (top layers) and chemoautotrophs (underneath): a living stromatolite (large mats in shark bay: modern day mats vs. stromatolites. Mat: instinctive layered structure created by sediment deposition layers of sediment adhere to microbes. Stromatolites: similarity with layered structure of ancient stromatolites. Suggests existence of microbial colonies at least 3. 5 byr ago. But can be difficult to distinguish from inorganic sedimentation processes: microfossils. Microfossil evidence for life by 2. 7 3. 0 byr ago is stronger. Contain a type of hydrocarbon molecule almost certainly associated with life. Hence, microfossil record suggests life originated by 3. 5 3. 0 byr ago: isotopes of carbon. Living organisms change the ratios of isotopes from their naturally occurring ones. E. g. , carbon-12 and carbon-13: ratio in nature is 89:1.
