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Ch. 25-26 (Life on Earth (Fossil Record (How rocks and fossils are dated,…

- - - - Oparin and Haldane hypothesized Earth's early environment was reducing; organic compounds could have formed into simpler ones
      - Early oceans were a solution or organic molecules from which life arose
      - Some evidence suggests the early atmosphere was made of mostly nitrogen and carbon dioxide
      - First organic compounds may have formed near volcanoes
      - Another hypothesis is that organic compounds were first produced in deep-sea hydrothermal vents
      - Meteorites may have been one more source of organic molecules
    - - DNA replication requires elaborate enzymatic machinery and an abundant supply of nucleotide building bocks
      - Suggests that self replicating molecules and a metabolism like source of building blocks may have appeared together in protocells
      - Necessary conditions may have been met in vesicles (fluid filled compartments enclosed by a membrane like structure
      - vesicles can exhibit certain properties of life, including simple reproduction and metabolism
    - - First genetic material was probably RNA not DNA
      - RNA's single strand allows it to form into whatever 3-D shape needed by their nucleotide sequence
      - the RNA molecule with the greatest ability to replicate itself will leave the most descendant molecules
      - vesicles with with self-replicating, catalytic RNA would differ from it's neighbors that lacked these molecules
      - If a vesicle could grow, split, and pass its RNA molecules to it's daughter, the daughters would be protocells
      - these inherited characteristics could be acted on by natural selection
      - Once RNA with genetic info appeared in protocells, many other changes became possible
        
        RNA could have provided the template for which DNA nucleotides were assembled
        
        DNA is more chemically stable and replicates more accurately than DNA, which would become more helpful as genomes grew larger
  - - - many of earth's orgs did not die in the right place at the right time to be preserved as fossils
        
        of the fossils that were formed, many were destroyed by later geological processes
        
        as a result, the known fossil record favors species that existed for a long time, were abundant in population, were widespread, and had hard shells or skeletons
    - - Radiometric dating
      - based on the decay of radioactive isotopes
      - a radioactive parent isotope decays to a daughter isotope at a character rate (Half-Life;50%)
      - Each type of radioactive isotope has a characteristic half life that is unaffected by temp, pressure, or other variable
      - Fossils contains isotopes of elements that accumulated in the organisms when they were alive (think of carbon-12 and carbon-14)
      - The carbon-12/14 method works for fossils up to 75k years old
      - Determining age in sedimentary rocks can be challenging, as most orgs do not use isotopes with long half lives to build their bones or shells
    - - some fossils provide a detailed look at the origin of new groups of orgs
      - (Look at evolution of mammals)