Unveiling Geologic Time & Mass Extinctions

2. Chapter Menu Lesson 1:Geologic Time and Mass Extinction Lesson 2:Early Earth History Lesson 3:Middle and Recent Earth History Click on a hyperlink to view the corresponding lesson.

3. 8.1 Geologic Time and Mass Extinction index fossil mass extinction catastrophic event

4. 8.1 Geologic Time and Mass Extinctions Development of the Geologic Time Scale • The changes that have occurred in Earth’s history are recorded on a time line called the geologic time scale. • The time scale’s units are uneven because extinctions, growth rates, and environmental changes happen at different rates.

5. 8.1 Geologic Time and Mass Extinctions Index Fossils • An index fossil is the remains of a species that existed over vast regions of Earth for a short period of time. • Special criteria are used to identify index fossils.

6. 8.1 Geologic Time and Mass Extinctions Index Fossils (cont.)

7. 8.1 Geologic Time and Mass Extinctions Divisions of the Geologic Time Scale • No two divisions of time have the same number of years. • The largest divisions are eons, then eras, periods, and epochs.

8. 8.1 Geologic Time and Mass Extinctions Divisions of the Geologic Time Scale (cont.) Divisions of the Geologic Time Scale (cont.)

9. 8.1 Geologic Time and Mass Extinctions Divisions of the Geologic Time Scale (cont.) Divisions of the Geologic Time Scale (cont.)

10. 8.1 Geologic Time and Mass Extinctions Divisions of the Geologic Time Scale (cont.) Divisions of the Geologic Time Scale (cont.)

11. 8.1 Geologic Time and Mass Extinctions Divisions of the Geologic Time Scale (cont.) Divisions of the Geologic Time Scale (cont.)

12. 8.1 Geologic Time and Mass Extinctions Eras • The Phanerozoic eon is divided into three eras. • Paleozoic era: dominated by invertebrate marine organisms • Mesozoic era: dinosaurs and mammals lived on land • Cenozoic era: humans evolved, continues today

13. 8.1 Geologic Time and Mass Extinctions Periods and Epochs • The Cenozoic era is divided into the Paleogene, Neogene, and Quaternary periods. • The Quaternary period began 1.8 million years ago and is divided into epochs. • The Pleistocene epoch ended about 8,000 years ago, and we now live in the Holocene epoch.

14. 8.1 Geologic Time and Mass Extinctions What are mass extinctions? • Mass extinction is the dying off of many species at one time. • A greater abundance of fossils in one rock layer compared to other layers indicates a mass extinction. • Mass extinctions happen over a great span of time.

15. 8.1 Geologic Time and Mass Extinctions Possible Causes of Mass Extinctions • A catastrophic event causes drastic change in the numbers of organisms of species over a short period in geologic time. • Not all catastrophic events cause mass extinction. • Types of events that can cause mass extinction include changes in climate, volcanic eruptions, and asteroid impacts.

16. 8.1 Geologic Time and Mass Extinctions Climate Change • There is evidence that some mass extinctions were caused by sudden climate change. • Species that cannot survive a change in climate become extinct. • Climate change can be caused by volcanic eruptions or asteroid impacts, and can result in global warming or cooling.

17. 8.1 Geologic Time and Mass Extinctions Global Warming • Greenhouse gases in the atmosphere may contribute to global warming—a global increase in atmospheric temperature. • Global warming causes a decrease in oxygen levels in water, and an increase in sea levels. • May have been the cause for the Devonian mass extinction

18. 8.1 Geologic Time and Mass Extinctions Global Cooling • Global cooling could lower sea levels as more water is frozen in glacial ice. • Less water means fewer warm, shallow-water environments. • May have initiated the Ordovician mass extinction

19. 8.1 Geologic Time and Mass Extinctions Volcanoes • Eruptions can be explosive or non-explosive. • The dust, ash, lava, and gas emitted from volcanic eruptions can affect climate and organisms. • A volcanic eruption is one hypothesis proposed to explain the mass extinction at the end of the Cretaceous period.

20. 8.1 Geologic Time and Mass Extinctions Basalt Flows • Non-explosive floods of molten basalt emit the largest volume of matter of any eruptions. • Geologic evidence shows that large basalt flows occurred during the Permian and Cretaceous mass extinctions.

21. 8.1 Geologic Time and Mass Extinctions Volcanic Haze • The gases produced by basalt flows cause a volcanic haze effect. • Sulfur dioxide gas is released and acid clouds form, preventing the Sun’s ultraviolet rays from reaching Earth. • Global cooling occurs over months and years. • Heat becomes trapped in the atmosphere and global temperatures increase.

22. 8.1 Geologic Time and Mass Extinctions Asteroid Impacts • Scientists believe an asteroid impact in Mexico may have contributed to the Cretaceous mass extinction.

23. 8.1 Geologic Time and Mass Extinctions Asteroid Impacts (cont.) • Scientists propose that this impact sent enough dust and materials into the atmosphere to block sunlight. • Global cooling after the impact turned to global warming as carbon dioxide was released from burning plants.

24. 8.1 Geologic Time and Mass Extinctions The Debate • Evidence supports the idea that many species became extinct at the end of the Cretaceous period because of asteroids. • But the impact did not cause all the extinctions. • Many species became extinct before the impact, and the rate of extinction was increasing before the impact.

25. 8.1 Geologic Time and Mass Extinctions Lesson 1 Review • A • B • C • D Which describes the divisions of the geologic time scale in order of longest to shortest units of time? Aeons, eras, periods, epochs Beons, epochs, eras, periods Cepochs, eons, periods, eras Depochs, eons, eras, periods

26. 8.1 Geologic Time and Mass Extinctions Lesson 1 Review • A • B • C • D What is the likely immediate outcome of an explosive volcanic eruption that sends dust into the atmosphere? Aglobal warming B global cooling C basalt flows D volcanic haze

27. 8.1 Geologic Time and Mass Extinctions Lesson 1 Review • A • B • C • D What type of eruption emits the largest volume of matter? A basalt flows B explosive eruptions C non-explosive eruptions D volcanic haze

28. End of Lesson 1

29. 8.2 Early Earth History cyanobacteria vertebrate amniote

30. 8.2 Early Earth History Life on Earth Changes • Paleontologists discovered that the system used to classify modern organisms could be used to classify fossils. • Fossils from rock layers that are touching are more similar than fossils from widely separated layers. • The more recent a fossil was formed, the more it resembles a living organism.

31. 8.2 Early Earth History Life on Earth Changes (cont.)

32. 8.2 Early Earth History Precambrian Time • Precambrian rocks are difficult to study because they have undergone metamorphism or been destroyed. • Precambrian fossils are not abundant but provide a lot of information about Earth’s early atmosphere and environment.

33. 8.2 Early Earth History The Precambrian Atmosphere • Archean sediments contain large amounts of pyrite and uraninite. • Today’s atmosphere contains oxygen that quickly destroys these minerals through oxidation. • Earth’s early atmosphere had very little oxygen.

34. 8.2 Early Earth History Ozone • The absence of oxygen suggests there was no ozone layer during Precambrian time. • Without ozone, ultraviolet rays cause death or mutations in cells. • Changes in one gene in an organism could result in new life forms many generations later.

35. 8.2 Early Earth History The First Organisms • Cyanobacteria—one of the earliest organisms. • Stromatolites are mounds of alternating thin-layered sediments and photosynthetic cyanobacteria that take in carbon dioxide and release oxygen.

36. 8.2 Early Earth History A Changing Environment • Oxygen levels rose slowly as cyanobacteria and other early-life forms released oxygen. • Natural selection favored organisms that could tolerate or use oxygen. • The amount of ozone in the atmosphere increased.

37. 8.2 Early Earth History Soft-Bodied Organisms • The first invertebrate organisms—animals without backbones—appeared during the Proterozoic eon. • Ediacaran fauna

38. 8.2 Early Earth History The Paleozoic Era • The first appearance of fossils of organisms made from hard parts marks the end of the Proterozoic eon. • Because hard parts fossilize easier, fossils are easier to find in Paleozoic rocks than Precambrian rocks.

39. 8.2 Early Earth History The Cambrian Explosion • During a relatively short period of time, the number of animals with shells greatly increased. • Invertebrates—sponges, jellies, corals—also evolved during the Cambrian explosion.

40. 8.2 Early Earth History Invertebrates of the Paleozoic Era • Throughout the Paleozoic era, the oceans contained a wide variety of invertebrate organisms. • Corals, brachiopods, crinoids, bryozoans • Ordovician period, Silurian period

41. 8.2 Early Earth History Vertebrates of the Paleozoic Era • Vertebrates—animals with backbones—evolved during the early Paleozoic era. • The first of these lived in the oceans. • Bony fish with bony rays that supported their fins • Bony fish with thick fins supported by large bones and muscles

42. 8.2 Early Earth History A New Egg • A new organism that could lay its eggs on land evolved during the early Pennsylvanian period. • Amniotes laid water-tight, amniotic eggs and could spend all their time on land. • Mammals, dinosaurs, and reptiles evolved from amniotes.

43. 8.2 Early Earth History Plants of the Paleozoic Era • During the Ordovician period, plants began spreading onto land. • Early land plants were small and lived in moist areas because they could not move water to all their parts.

44. 8.2 Early Earth History Plants of the Paleozoic Era (cont.) • Plants with vascular systems that could move nutrients between roots and leaves then evolved. • New plants developed quickly.

45. 8.2 Early Earth History Paleozoic Extinctions • The Paleozoic era ended with the late Permian extinction—90% of marine and 70% of land species.

46. 8.2 Early Earth History Paleozoic Extinctions (cont.) • The uplifting formation of Pangaea, or ash and sulfur released from the Siberian Traps may explain the Permian extinction.

47. 8.2 Early Earth History Lesson 2 Review • A • B • C • D Which is not a characteristic of Earth’s early atmosphere during the Precambrian time? A very little oxygen B no ozone layer C iron in minerals quickly oxidized D organisms were exposed to ultraviolet rays

48. 8.2 Early Earth History Lesson 2 Review • A • B • C • D What were some of the first vertebrates? A brachiopods B trilobites C edicacaran fauna D bony fish

49. 8.2 Early Earth History Lesson 2 Review • A • B • C • D What ended the Paleozoic era? A Ordovician extinction B Devonian extinction CPermian extinction DCambrian extinction

50. End of Lesson 2