The Origin and Evolutionary History of Life

1. The Origin and Evolutionary History of Life Chapter 21

2. Learning Objective 1 • What conditions do geologists think existed on early Earth?

3. Early Earth

4. The Origin of Life • Biologists generally agree • life originated from nonliving matter • by chemical evolution • Origin of life is difficult to test experimentally • testable hypotheses about chemical evolution

5. KEY CONCEPTS • Although there is no direct fossil evidence of the origin of life, biochemical experiments have demonstrated how complex organic molecules, found in all living organisms, may have formed

6. 4 Requirements for Chemical Evolution 1. Absence of oxygen • oxygen would oxidize abiotically produced organic molecules 2. Energy • to form organic molecules

7. 4 Requirements for Chemical Evolution 3. Chemical building blocks • water, minerals, gases in atmosphere • to form organic molecules 4. Sufficient time • for molecules to accumulate and react

8. Learn more about conditions on early Earth by clicking on the figure in ThomsonNOW.

9. Learning Objective 2 • Contrast the prebiotic soup hypothesis and the iron–sulfur worldhypothesis

10. Chemical Evolution • Prebiotic soup hypothesis • organic molecules formed near Earth’s surface in “sea of organic soup” or on rock or clay surfaces • Iron–sulfur world hypothesis • organic molecules produced at hydrothermal vents in deep ocean floor

11. Miller and Urey’s Experiment

12. Electrodes NH3 CH4 H2 H2O To vacuum Spark chamber Condenser Boiling chamber Organic molecules collect in the trap Heat source Fig. 21-2, p. 449

13. Insert “Miller's reaction chamber experiment” Miller_Urey.swf

14. See the Miller–Urey experiment unfold by clicking on the figure in ThomsonNOW.

15. Learning Objective 3 • What major steps are hypothesized to have occurred in the origin of cells?

16. The Origin of Cells • Macromolecules • assembled from small organic molecules • Protobionts (macromolecular assemblages) • formed from macromolecules • Cells • arose from protobionts

17. Microspheres

18. RNA WorldModel • RNA • first informational molecule to evolve • progression toward self-reproducing cell • Natural selection at molecular level • resulted in information sequence • DNA → RNA → protein

19. RNA Molecules

20. Large pool of RNA molecules Selection for ability to catalyze a chemical reaction Molecules with some ability to catalyze the reaction Amplification and mutation to create large pool of similar RNA molecules Repeat the selection–amplification–mutation process Molecules with best ability to catalyze the reaction Fig. 21-4, p. 451

21. Large pool of RNA molecules Selection for ability to catalyze a chemical reaction Molecules with some ability to catalyze the reaction Amplification and mutation to create large pool of similar RNA molecules Repeat the selection–amplification–mutation process Molecules with best ability to catalyze the reaction Stepped Art Fig. 21-4, p. 451

22. Learning Objective 4 • How did the evolution of photosynthetic autotrophs affected both the atmosphere and other organisms?

23. The First Cells • Prokaryotic heterotrophs • obtained organic molecules from environment • probably anaerobes • Autotrophs • evolved later • produced organic molecules by photosynthesis

24. Photosynthesis • Generated oxygen in atmosphere • changed early life • permitted evolution of aerobes • Aerobes • use oxygen for efficient cellular respiration

25. Ozone

26. Sun Ultraviolet rays 3(O2) Upper atmosphere 2(O3) Lower atmosphere Fig. 21-6, p. 453

27. Learning Objective 5 • What is the hypothesis of serial endosymbiosis?

28. Serial Endosymbiosis • Eukaryotic cells arose from prokaryotic cells • Certain eukaryotic organelles (mitochondria, chloroplasts) evolved from prokaryotic endosymbionts • incorporated within larger prokaryotic hosts

29. Serial Endosymbiosis

30. ORIGINAL PROKARYOTIC HOST CELL DNA Aerobic bacteria Multiple invaginations of the plasma membrane Endoplasmic reticulum and nuclear envelope form from the plasma membrane invaginations (not part of serial endosymbiosis) Aerobic bacteria become mitochondria Photosynthetic bacteria... ... become chloroplasts EUKARYOTIC CELLS: ANIMALS, FUNGI, SOME PROTISTS EUKARYOTIC CELLS: PLANTS, SOME PROTISTS Fig. 21-7, p. 454

31. Insert “The endosymbiont theory” endosymbiont_theory_m.swf

32. Learn more about endosymbiosis by clicking on the figure in ThomsonNOW.

33. KEY CONCEPTS • Photosynthesis, aerobic respiration, and eukaryotic cell structure represent several major advances that occurred during the early history of life

34. Learning Objective 6 • What are the distinguishing organisms and major biological events of the Ediacaran period and the Paleozoic, Mesozoic, and Cenozoic eras

35. Proterozoic Eon • 2500 mya to 542 mya • life consisted of prokaryotes • About 2.2 bya • first eukaryotic cells appeared

36. Ediacaran Period • Ediacaran period • 600 mya to 542 mya • last period of Proterozoic eon • Ediacaran fossils • oldest known fossils of multicellular animals • Ediacaran fauna • small, soft-bodied invertebrates

37. An Ediacaran Sea

38. The Paleozoic Era (1) • Began about 542 mya • lasted about 291 million years • Many plants and animals appeared • all major plants (except flowering plants) • all animal phyla • reptiles • fishes and amphibians flourished

39. Cambrian Radiation

40. Fig. 21-9a, p. 457

41. Fig. 21-9b, p. 457

42. Fig. 21-9c, p. 457

43. Devonian Period

44. (b) Pterapsis (c) Jamoytius (a) Thelodus Fig. 21-10, p. 458

45. Carboniferous Period

46. The Paleozoic Era (2) • Greatest mass extinction of all time • at end of Paleozoic era (251 mya) • > 90% of marine species extinct • 70% of land-dwelling vertebrate genera • many plant species

47. The Mesozoic Era • Began about 251 mya • lasted about 185 million years • Dinosaurs dominated • reptiles diversified • insects flourished • flowering plants appeared • birds appeared • early mammals appeared

48. Triassic Period

49. Cretaceous Period

50. Cretaceous Period • 66 mya • end of Cretaceous period • many species abruptly became extinct • Collision of extraterrestrial body with Earth • may have caused dramatic climate changes • resulted in mass extinction