The History of Life on Earth

1. The History of Life on Earth As We Know It

2. The History of Earth • Earth is ~ 4.5 billion years old • Earth’s history is divided into four eons • Hadean Eon: (Gk: Hades - the netherworld) • Archean Eon: (Gk: Arche - ancient) • Proterozoic Eon: (Gk: Protero - former) • Phanaerozoic Eon (Gk: Phanero - visible, apparent)

3. The History of Earth • The most recent eon is divided into three eras • Paleozoic Era (Gk: Paleo - ancient) • Mesozoic Era (Gk: Meso - middle) • Cenozoic Era (Gk: Ceno - recent)

4. The History of Earth • eras of the modern eon are divided into periods • Paleozoic Era • Cambrian Period • Ordovician Period • Silurian Period • Devonian Period • Carboniferous Period • Permian Period

5. The History of Earth • eras of the modern eon are divided into periods • Mesozoic Era • Triassic Period • Jurassic Period • Cretaceous Period • Cenozoic Era • Tertiary Period • Quaternary Period

6. Earth’s History: Changing ConditionsTable 22.1

7. Earth’s History: Changing Conditions • atmospheric oxygen concentration has risen from near 0 to ~21% • See Figure 22.3

8. Earth’s History: Changing Conditions • atmospheric oxygen concentration has risen from near 0 to ~21% • mean temperature has fluctuated significantly • sea level has fluctuated significantly • continents have entirely changed positions • relatively gradual changes rapid, climate-changing events • “catastrophic” events have modified the evolution of life

9. Log-log Oxygen levelsFigure 22.4

10. Changes in Earth’s Mean Temperature in the Modern EonFigure 22.5

11. Changes in Sea Level in theModern EonFigure 22.2

12. Earth’s History: Changing Conditions • atmospheric oxygen concentration has risen from near 0 to ~21% • mean temperature has fluctuated significantly • sea level has fluctuated significantly • continents have entirely changed positions

13. mid-Cambrian Continental Drift(~510 mya)(forming Gondwana)Figure 22.9

14. Devonian Drift (400-350 mya)Figure 22.11

15. Permian Drift (formation of Pangaea)[~290-250 mya]Figure 22.13

16. Cretaceous Continental Positions(~100 mya)Figure 22.15

17. “catastrophic” events have modified the evolution of life • Dramatic climate change • End of Ordovician, Devonian, Permian, Triassic, Cretaceous • Volcanism • End of Permian • During Triassic, Cretaceous • Meteorite collisions • End of Triassic, End of Cretaceous

18. Figure 22.6

19. “catastrophic” events have modified the evolution of life • several mass extinctions have occurred • repeatedly, up to 75% of species became extinct • afterward, new life forms proliferated and became dominant - evolutionary radiation

20. Dating events in Earth’s history • absolute dates are estimated from the decay of radioactive elements • relative ages are determined by the position in a series of rock layers • remains of dead organisms are mineralized (fossilized) under the right conditions • anaerobic • undisturbed • proper geochemistry

21. Dating events in Earth’s history • absolute dates are estimated from the decay of radioactive elements half-lives of some radioactive isotopes 14C - 5,700 years 40K - 1.3 x 106 years 238U - 4.5 x 109 years

22. Figure 22.1

23. Figure 22.8

24. Figure 22.7

25. changing faunasFigure 22.17

26. The History of Life on Earth • Earth’s past biotas are represented by fossilized remains ~300,000 described species • Earth’s different ages are characterized by different types of fossils • boundaries defining the eras and periods of the modern eon represent changes in fossil assemblages

27. The History of Life on Earth • Fossils from successive ages reveal patterns • particular fossil types are found in rocks of the same age • new types of organisms appear sequentially in younger rock layers • types of organisms in shallower (younger) layers more closely resemble extant organisms • the appearance of new types of organisms occurred at different rates through time

28. three dominant world faunasFigure 22.17

29. The History of Life on Earth • Fossils from successive ages reveal patterns • three faunas dominated animal life over time • size and complexity of organisms increased with time • predators became more efficient; defenses became more effective • extinction happened • a typical species exists for ~10,000,000 years • ~99% of species are extinct

30. The History of Life on Earth • Fossils from successive ages reveal patterns • few innovations • novel structures are rare • most diversity is variation on existing body plans

31. The History of Life on Earth • Fossils from successive ages reveal patterns • microevolutionary change: • change that modifies species

32. Sticklebacks - no predatory fish, short spinesFigure 22.20

33. The History of Life on Earth • Fossils from successive ages reveal patterns • macroevolutionary change: • change that produces new types of organisms

34. The History of Life on Earth • The history of Earth is characterized by dramatic changes • gradual structural and climatic changes punctuated by catastrophic events • The history of life on Earth is characterized by increases in size, complexity, competition & predation

35. Geologic History from a Biologist’s Point of View