BISC 120L Midterm 2 review - BISC 120L Midterm#2 Review...

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BISC 120L Midterm #2 Review Chapter 26 Earth formed about 4.6 billion years ago, along with the rest of the solar system Very simple cells produced through a series of steps: 1. Abiotic synthesis of small organic molecules Experiments (Miller exp) simulating an early Earth atmosphere produced organic molecules from inorganic precursors, but such an atmosphere on early Earth is unlikely. used: H2, Methane (CH4), and NH4 (reducing) currently thought: N2 and CO2 gases (neither red. or ox.) but with reducing “pockets” submerged volcanoes and deep-sea vents some may have come from outerspace, eg meteorites, not a major source of organics 2. Joining of these small molecules into polymers Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock 3. Packaging of molecules into “protobionts” Protobionts are aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structure Ex: small membrane-bounded droplets called liposomes can form when lipids or other organic molecules are added to water 4. Origin of self-replicating molecules RNA molecules called ribozymes have been found to catalyze many different reactions, including: Self-splicing Making complementary copies of short stretches of their own sequence or other short pieces of RNA Fossils: Sedimentary strata reveal the relative ages of fossils a layer or a series of layers of rock in the ground Index fossils are similar fossils found in the same strata in different locations They allow strata at one location to be correlated with strata at another location Brachiopods – look like Ariel’s seashells The absolute ages of fossils can be determined by radiometric dating parent isotope becomes daughter eg 14C to 14N - yields info for about 75k yrs potassium-40 for rocks Half-life - the time that it take for 1/2 of the original sample to decay ~ unaffected by temp, pressure, and other variables The geologic record is divided into three eons: the Archaean (>2500 MYA) , the Proterozoic (>542 MYA) , and the Phanerozoic (<542MYA) the Phanerozoic is divided into three eras: the Paleozoic (541-251) , Mesozoic (251-65) , and Cenozoic (65-now) MYA
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boundaries marked by extinctions The Permian extinction killed about 96% of marine animal species and 8 out of 27 orders of insects (~260 MYA) It may have been caused by volcanic eruptions The Cretaceous extinction doomed many marine and terrestrial organisms, notably the dinosaurs It may have been caused by a large meteor impact (~65MYA) support - iridium (a compound found in asteroids - rare on earth) is found in layers associated with this time-period The oldest known fossils are stromatolites , rocklike structures composed of many layers of bacteria and sediment Stromatolites date back 3.5 billion years ago Prokaryotes Chemiosmotic Mechanism of ATP synthesis use proton gradient to generate via ATPase Oxygenic photosynthesis probably evolved about 3.5 billion years ago in
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