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 world hypothesis

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. Organic molecules collect in the trap Heat source
Electrodes
NH3
CH4
To vacuum
H2O H2
Spark chamber
Condenser
Figure 21.2: Miller and Urey’s experiment in chemical evolution.
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 World Model RNA Natural selection at molecular level
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
Figure 21.4: In vitro evolution of 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
Figure 21.4: In vitro evolution of RNA molecules.
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 Autotrophs
obtained organic molecules from environment
probably anaerobes
Autotrophs
evolved later
produced organic molecules by photosynthesis

24. Photosynthesis Generated oxygen in atmosphere Aerobes
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
Figure 21.6: The formation of ozone.
Ozone (O3) forms in the upper atmosphere when ultraviolet radiation from the sun breaks the double bonds of oxygen molecules.
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...
Figure 21.7: Serial endosymbiosis.
... 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 About 2.2 bya
life consisted of prokaryotes
About 2.2 bya
first eukaryotic cells appeared

36. Ediacaran Period Ediacaran period Ediacaran fossils Ediacaran fauna
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 Figure 21.9: Fossils from the Cambrian Radiation.
All three of these fossils were discovered in the Burgess Shale in the Canadian Rockies of British Columbia.
Fig. 21-9a, p. 457

41. Fig. 21-9b, p. 457 Figure 21.9: Fossils from the Cambrian Radiation.
All three of these fossils were discovered in the Burgess Shale in the Canadian Rockies of British Columbia.
Fig. 21-9b, p. 457

42. Fig. 21-9c, p. 457 Figure 21.9: Fossils from the Cambrian Radiation.
All three of these fossils were discovered in the Burgess Shale in the Canadian Rockies of British Columbia.
Fig. 21-9c, p. 457

43. Devonian Period

44. (b) Pterapsis (c) Jamoytius (a) Thelodus Fig. 21-10, p. 458
Figure 21.10: Ostracoderms.
Ostracoderms, primitive jawless fishes that lived in the Devonian period, ranged from 10 to 50 cm (4 to 20 in) in length.
(a) Thelodus
Fig , 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 Dinosaurs dominated
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 Collision of extraterrestrial body with Earth
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

51. Cenozoic Era From 66 mya to present
flowering plants, birds, insects, mammals diversified greatly
Late Miocene and Early Pliocene epochs
human ancestors appeared in Africa

52. The Fossil Record

53. The saurischian pelvis
Saurischians
Ilium
Hip socket
Pubis
Ischium
Coelophysis
Figure 21.15: Saurischian and ornithischian dinosaurs.
In each dinosaur figure, the pale yellow femur is shown relative to the pelvic bone.
The saurischian pelvis
Fig a, p. 461

54. The ornithischian pelvis
Ornithischians
Ilium
Hip socket
Pubis
Ischium
Figure 21.15: Saurischian and ornithischian dinosaurs.
In each dinosaur figure, the pale yellow femur is shown relative to the pelvic bone.
Stegosaurus
The ornithischian pelvis
Fig b, p. 461

55. KEY CONCEPTS
The fossil record tells us much of what we know about the history of life, such as what kinds of organisms existed and where and when they lived

56. Fossil Trilobites

57. KEY CONCEPTS
Certain organisms appear in the fossil record, then disappear and are replaced by others

58. Stromatolites

59. KEY CONCEPTS
Scientists identify and demonstrate relationships among fossils in rock layers from different periods of geologic time