The Origin and Evolution of Life on Early Earth

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