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Chapter 20

Chapter 20. The Origin and Evolutionary History of Life. Conditions on early Earth Age of Earth is ~4.6 billion years Atmosphere had little free O 2 Included CO 2 , H 2 O, CO, H 2 , N 2 Maybe also NH 3 , H 2 S, CH 4. Requirements for chemical evolution to produce life Absence of oxygen

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Chapter 20

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  1. Chapter 20 The Origin and Evolutionary Historyof Life

  2. Conditions on early Earth • Age of Earth is ~4.6 billion years • Atmosphere had little free O2 • Included CO2, H2O, CO, H2, N2 • Maybe also NH3, H2S, CH4

  3. Requirements for chemical evolution to produce life • Absence of oxygen • Energy • Chemical building blocks • Sufficient time

  4. Prebiotic soup hypothesis • Molecules formed near the Earth’s surface • Sugars, nucleotides, amino acids formed spontaneously

  5. Miller-Urey experiment

  6. Iron-sulfur world hypothesis • Organic molecules formed at hydrothermal vents on the ocean floor • Laboratory simulations show catalyst effects of iron and nickel sulfides

  7. Origin of cells • Spontaneous assembly of small organic molecules into macromolecules • Protobionts similar to cells • Binary fission • Homeostasis • Catalytic activity

  8. Microspheres – a type of protobiont

  9. Microspheres • Formed from water and polypeptides • Electric gradient on surface • Selective permeability

  10. RNA world • Self-replicating RNA molecules • Function as both enzyme and substrate for replication • Ribozyme is enzymatic RNA • First step in evolution of theDNA / RNA / protein system

  11. Directed evolution • Large pool of RNA molecules with different sequences • Selected for ability to catalyze a reaction • Amplify / mutate / repeat

  12. Directed evolution

  13. In the RNA world, ribozymes catalyzed protein synthesis • DNA formed from double strands of RNA • DNA more stable than RNA

  14. The first cells • Heterotrophs that feed on organic molecules • Anaerobic fermentation process to obtain energy

  15. Autotrophs • Selected after organic molecule food stock became scarce • Photosynthetic production of organic molecules • Cyanobacteria split water molecules and released oxygen

  16. Aerobes • More efficient energy production using oxygen respiration • Significant oxygen in the atmosphere by 2 bya

  17. Formation of the ozone layer • Ultraviolet radiation forms O3 from O2 in the upper atmosphere • Prevents UV from reaching Earth • Decreased mutagenesis • Enabled organisms to live in surface waters and on land

  18. Ozone formation

  19. Eukaryotes arose from prokaryotes • Endosymbiont theory • Mitochondria and chloroplasts derived from prokaryotes • Ingested but not digested • Reproduced along with host cell

  20. Endosymbiont theory

  21. Geological eras • Paleozoic • 543 mya - 251 mya • Mesozoic • 251 mya - 65 mya • Cenozoic • 65 mya - present

  22. Using a clock to represent biological time

  23. Precambrian time • Before 543 mya • Bacteria • Protists • Fungi • Simple multicellular animals

  24. Cambrian explosion • All animal phyla established • Many new body plans • Bizarre, extinct phyla

  25. Ordovician period • Shallow seas covered land • Cephalopods • Coral reefs • Jawless fishes

  26. Silurian period • Jawed fishes • Terrestrial plants • Air-breathing animals

  27. Devonian period • Bony fishes • Amphibians • Wingless insects • All major plant groups except for flowering plants established

  28. Carboniferous period • Swamp forests • Reptiles • Winged insects

  29. Carboniferous forest

  30. Permian period • Therapsids • Reptilian ancestors of mammals • Seed plants dominant • Ended the Paleozoic with the greatest mass extinction • 90% of marine species • 70% of land vertebrates

  31. Mesozoic Era

  32. Triassic period • Thecodonts • Ancestors of dinosaurs and birds • Pleiosaurs and ichthyosaurs • Pterodonts • First mammals • Small insectivores

  33. Jurassic and Cretaceous periods • Saurischians • Ancestors of lizards • Ornithischians • Ancestors of birds • Ended with mass extinction caused by a meteorite impact

  34. Saurischians

  35. Ornithischians

  36. Cenozoic Era

  37. Tertiary period • Diversification of flowering plants, birds, insects, mammals • Quaternary period • Genus Homo • Large mammals

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