The History of Life on Earth

1
CHAPTER 20 The History of Life on Earth
2
Chapter 20 The History of Life on Earth

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

3
Chapter 20 The History of Life on Earth

• Rates of Evolutionary Change
• Patterns of Evolutionary Change
• The Future of Evolution

4
The History of Life on Earth

• 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.
• 4

5
How Do We Know that Earth is Ancient?

• The relative ages of rock layers in Earths crust
  can be determined from their positions relative
  to one another and from their embedded fossils.
• 5

6
How Do We Know that Earth is Ancient?

• Radioisotopes supplied the key for assigning
  absolute ages to rocks.
• 6

7
How Do We Know that Earth is Ancient?

• Earths geological history is divided into eras
  and periods.
• The boundaries between these units are based on
  differences between their fossil biotas.
• Review Table 20.1
• 7

8
Table 20.1
table 20-01-2.jpg

• Table 20.1

9
How Has Earth Changed over Time?

• Unidirectional physical changes on Earth include
  gradual cooling and weakening of the forces that
  cause continental drift.
• 9

10
How Has Earth Changed over Time?

• Earths early atmosphere lacked free oxygen.
• 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.
• Review Figure 20.2
• 10

11
20.2
figure 20-02.jpg

• Figure 20.2

12
How Has Earth Changed over Time?

• Throughout Earths history the continents have
  shifted, sometimes separating, at other times
  colliding.
• Review Figures 20.10, 20.11, 20.13, 20.15
• 12

13
20.10
figure 20-10.jpg

• Figure 20.10

14
20.11
figure 20-11.jpg

• Figure 20.11

15
20.13
figure 20-13.jpg

• Figure 20.13

16
20.15
figure 20-15.jpg

• Figure 20.15

17
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.
• Review Figures 20.3, 20.4
• 17

18
20.3
figure 20-03.jpg

• Figure 20.3

19
20.4
figure 20-04.jpg

• Figure 20.4

20
How Has Earth Changed over Time?

• 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.
• 20

21
The Fossil Record

• Much of what we know about the history of life on
  Earth comes from the study of fossils.
• 21

22
The Fossil Record

• The fossil record, although incomplete, reveals
  broad patterns in the evolution of life.
• About 300,000 fossil species have been described.
  
• 22

23
The Fossil Record

• 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
• 23

24
20.7
figure 20-07.jpg

• Figure 20.7

25
20.8 Part 1
figure 20-08a.jpg

• Figure 20.8 Part 1

26
20.8 Part 2
figure 20-08b.jpg

• Figure 20.8 Part 2

27
20.8 Part 3
figure 20-08c.jpg

• Figure 20.8 Part 3

28
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.
• 28

29
Life in the Remote Past

• Diversity exploded during the Cambrian period.
• Review Figure 20.10
• 29

30
Life in the Remote Past

• Geographic differentiation of biotas increased
  during the Mesozoic era.
• 30

31
Life in the Remote Past

• The modern biota evolved during the Cenozoic era.
  
• 31

32
Rates of Evolutionary Change

• Rates of evolutionary change have been very
  uneven.
• 32

33
Rates of Evolutionary Change

• Rapid rates of evolution occur when changes to
  the physical or biological environment create
  conditions that favor new traits.
• Review Figure 20.16
• 33

34
20.16
figure 20-16.jpg

• Figure 20.16

35
Patterns of Evolutionary Change

• Truly novel features of organisms have evolved
  infrequently.
• Most evolutionary changes are the result of
  modifications of already existing structures.
• 35

36
Patterns of Evolutionary Change

• Three major faunas have dominated animal life on
  Earth.
• Review Figure 20.17
• 36

37
20.17
figure 20-17.jpg

• Figure 20.17

38
Patterns of Evolutionary Change

• 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.
• Review Figure 20.18
• 38

39
20.18
figure 20-18.jpg

• Figure 20.18

40
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.
• 40