1. Chapter 20: The History of Life on Earth CHAPTER 20 The History of Life on Earth

2. Chapter 20: The History of Life on Earth The History of Life on Earth The History of Life on Earth How Do We Know that Earth Is Ancient? How Do We Know that Earth Is Ancient? How Has Earth Changed over Time? How Has Earth Changed over Time? The Fossil Record The Fossil Record Life in the Remote Past Life in the Remote Past

3. Chapter 20: The History of Life on Earth Rates of Evolutionary Change Rates of Evolutionary Change Patterns of Evolutionary Change Patterns of Evolutionary Change The Future of Evolution The Future of Evolution

4. Chapter 20: The History of Life on Earth The History of Life on Earth Changes that take effect during the lifetimes of species constitute microevolution.Changes that take effect during the lifetimes of species constitute microevolution. Those that involve the appearance of new species and evolutionary lineages are called macroevolution.Those that involve the appearance of new species and evolutionary lineages are called macroevolution.4

5. Chapter 20: The History of Life on Earth How Do We Know that Earth is Ancient? The relative ages of rock layers in Earth’s crust can be determined from their positions relative to one another and from their embedded fossils.The relative ages of rock layers in Earth’s crust can be determined from their positions relative to one another and from their embedded fossils.5

6. Chapter 20: The History of Life on Earth How Do We Know that Earth is Ancient? Radioisotopes supplied the key for assigning absolute ages to rocks.Radioisotopes supplied the key for assigning absolute ages to rocks.6

7. Chapter 20: The History of Life on Earth How Do We Know that Earth is Ancient? Earth’s geological history is divided into eras and periods.Earth’s geological history is divided into eras and periods. The boundaries between these units are based on differences between their fossil biotas.The boundaries between these units are based on differences between their fossil biotas. Review Table 20.1 20.1 7

8. Chapter 20: The History of Life on Earth Table 20.1 table 20-01-2.jpg

9. Chapter 20: The History of Life on Earth How Has Earth Changed over Time? Unidirectional physical changes on Earth include gradual cooling and weakening of the forces that cause continental drift.Unidirectional physical changes on Earth include gradual cooling and weakening of the forces that cause continental drift.9

10. Chapter 20: The History of Life on Earth How Has Earth Changed over Time? Earth’s early atmosphere lacked free oxygen.Earth’s early atmosphere lacked free oxygen. Oxygen accumulated after prokaryotes evolved the ability to use water as a source of hydrogen ions in photosynthesis. Oxygen accumulated after prokaryotes evolved the ability to use water as a source of hydrogen ions in photosynthesis. Increasing atmospheric oxygen allowed evolution of eukaryotes and multicellular organisms.Increasing atmospheric oxygen allowed evolution of eukaryotes and multicellular organisms. Review Figure 20.2 20.2 10

11. Chapter 20: The History of Life on Earth 20.2 Figure 20.2 figure 20-02.jpg

12. Chapter 20: The History of Life on Earth How Has Earth Changed over Time? Throughout Earth’s history the continents have shifted, sometimes separating, at other times colliding.Throughout Earth’s history the continents have shifted, sometimes separating, at other times colliding. Review Figures 20.10, 20.11, 20.13, 20.15 20.1020.1120.1320.1520.1020.1120.1320.1512

13. Chapter 20: The History of Life on Earth 20.10 Figure 20.10 figure 20-10.jpg

14. Chapter 20: The History of Life on Earth 20.11 Figure 20.11 figure 20-11.jpg

15. Chapter 20: The History of Life on Earth 20.13 Figure 20.13 figure 20-13.jpg

16. Chapter 20: The History of Life on Earth 20.15 Figure 20.15 figure 20-15.jpg

17. Chapter 20: The History of Life on Earth How Has Earth Changed over Time? Rapid climate change, massive volcanism, and major shifts in sea levels and ocean currents have all had dramatic effects on the evolution of life on Earth.Rapid climate change, massive volcanism, and major shifts in sea levels and ocean currents have all had dramatic effects on the evolution of life on Earth. Review Figures 20.3, 20.4 20.320.420.320.417

18. Chapter 20: The History of Life on Earth 20.3 Figure 20.3 figure 20-03.jpg

19. Chapter 20: The History of Life on Earth 20.4 Figure 20.4 figure 20-04.jpg

20. Chapter 20: The History of Life on Earth How Has Earth Changed over Time? External events, such as meteorite collisions, also have changed conditions on Earth.External events, such as meteorite collisions, also have changed conditions on Earth. A meteorite may have caused the abrupt mass extinction at the end of the Cretaceous period.A meteorite may have caused the abrupt mass extinction at the end of the Cretaceous period.20

21. Chapter 20: The History of Life on Earth The Fossil Record Much of what we know about the history of life on Earth comes from the study of fossils.Much of what we know about the history of life on Earth comes from the study of fossils.21

22. Chapter 20: The History of Life on Earth The Fossil Record The fossil record, although incomplete, reveals broad patterns in the evolution of life.The fossil record, although incomplete, reveals broad patterns in the evolution of life. About 300,000 fossil species have been described.About 300,000 fossil species have been described.22

23. Chapter 20: The History of Life on Earth The Fossil Record Fossils show that many evolutionary changes are gradual, but an incomplete record can falsely suggest or conceal times of rapid change.Fossils show that many evolutionary changes are gradual, but an incomplete record can falsely suggest or conceal times of rapid change. Review Figure 20.7, 20.8 20.720.820.720.8 23

24. Chapter 20: The History of Life on Earth 20.7 Figure 20.7 figure 20-07.jpg

25. Chapter 20: The History of Life on Earth 20.8 – Part 1 Figure 20.8 – Part 1 figure 20-08a.jpg

26. Chapter 20: The History of Life on Earth 20.8 – Part 2 Figure 20.8 – Part 2 figure 20-08b.jpg

27. Chapter 20: The History of Life on Earth 20.8 – Part 3 Figure 20.8 – Part 3 figure 20-08c.jpg

28. Chapter 20: The History of Life on Earth Life in the Remote Past The fossil record for Precambrian times is fragmentary, but fossils from Australia show that many lineages that evolved then may not have left living descendants.The fossil record for Precambrian times is fragmentary, but fossils from Australia show that many lineages that evolved then may not have left living descendants.28

29. Chapter 20: The History of Life on Earth Life in the Remote Past Diversity exploded during the Cambrian period.Diversity exploded during the Cambrian period. Review Figure 20.10 20.10 29

30. Chapter 20: The History of Life on Earth Life in the Remote Past Geographic differentiation of biotas increased during the Mesozoic era.Geographic differentiation of biotas increased during the Mesozoic era.30

31. Chapter 20: The History of Life on Earth Life in the Remote Past The modern biota evolved during the Cenozoic era.The modern biota evolved during the Cenozoic era.31

32. Chapter 20: The History of Life on Earth Rates of Evolutionary Change Rates of evolutionary change have been very uneven.Rates of evolutionary change have been very uneven.32

33. Chapter 20: The History of Life on Earth Rates of Evolutionary Change Rapid rates of evolution occur when changes to the physical or biological environment create conditions that favor new traits.Rapid rates of evolution occur when changes to the physical or biological environment create conditions that favor new traits. Review Figure 20.16 20.16 33

34. Chapter 20: The History of Life on Earth 20.16 Figure 20.16 figure 20-16.jpg

35. Chapter 20: The History of Life on Earth Patterns of Evolutionary Change Truly novel features of organisms have evolved infrequently.Truly novel features of organisms have evolved infrequently. Most evolutionary changes are the result of modifications of already existing structures.Most evolutionary changes are the result of modifications of already existing structures.35

36. Chapter 20: The History of Life on Earth Patterns of Evolutionary Change Three major faunas have dominated animal life on Earth.Three major faunas have dominated animal life on Earth. Review Figure 20.17 20.17 36

37. Chapter 20: The History of Life on Earth 20.17 Figure 20.17 figure 20-17.jpg

38. Chapter 20: The History of Life on Earth Patterns of Evolutionary Change Over evolutionary time, organisms have increased in size and complexity.Over evolutionary time, organisms have increased in size and complexity. Predation rates have also increased, resulting in the evolution of better defenses among prey species.Predation rates have also increased, resulting in the evolution of better defenses among prey species. Review Figure 20.18 Review Figure 20.1820.18 38

39. Chapter 20: The History of Life on Earth 20.18 Figure 20.18 figure 20-18.jpg

40. Chapter 20: The History of Life on Earth The Future of Evolution The agents of evolution continue to operate today, but human intervention, both deliberate and inadvertent, now plays an unprecedented role in the history of life.The agents of evolution continue to operate today, but human intervention, both deliberate and inadvertent, now plays an unprecedented role in the history of life.40