1. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Chapter 21: GEOLOGIC TIME—READING THE ROCK RECORD

2. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley This lecture will help you understand: The Rock Record-Relative Dating Radiometric Dating Geologic Time Precambrian Time The Paleozoic Era The Mesozoic Era The Cenozoic Era Early History in a Capsule

3. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Rock Record—Relative Dating Earth is ~4.5 billion years old. Compared to a single calendar year: —Formation of Earth Jan. 1 —Oldest rocksFeb. 26 —Bacterial lifeMar. 23 —DinosaursDec. 14 to 26 —Homo sapiensDec. 31 @11:50 pm —Human historyDec. 31 @11:59 pm

4. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Uniformitarianism Uniformitarianism is the assumption that Earth’s geology is the result of slow processes over long periods of time. Assumes that natural laws have been constant throughout geologic history.

5. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Rock Record— Relative Dating The rock record is like a very long, old book with many pages that are tattered, torn, indecipherable, and missing. Two methods of dating rock: Relative dating—relative age, the ordering of rocks in sequence by comparative ages Radiometric dating—absolute age, actual age of rock determined in a laboratory

6. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Rock Record— Relative Dating Original horizontality: New layers of sediment are horizontally laid down over older layers. Superposition: In undeformed sequences of rock, top layers are younger than bottom layers. Cross-cutting: A fault or intrusion that cuts into a rock is younger than the rock it cuts through.

7. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Rock Record— Relative Dating Inclusion: Any inclusion is older than the rock containing it. Lateral continuity: Allows us to date separated rock outcrops from similar characteristics. Faunal succession: Fossil organisms follow one another in a definite, irreversible time sequence.

8. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Three dikes (igneous intrusion) cut into a rock body. Which dike is the oldest, and which is the youngest? A.A is oldest, then B, and C is the youngest. B.C is oldest, then B, and A is the youngest. C.B is oldest, then A, and C is the youngest. D.A is oldest, then C, and B is the youngest. The Rock Record—Relative Dating CHECK YOUR NEIGHBOR

9. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Three dikes (igneous intrusion) cut into a rock body. Which dike is the oldest, and which is the youngest? A.A is oldest, then B, and C is the youngest. B.C is oldest, then B, and A is the youngest. C.B is oldest, then A, and C is the youngest. D.A is oldest, then C, and B is the youngest. The Rock Record—Relative Dating CHECK YOUR ANSWER

10. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The embedded rocks (inclusions) in the sedimentary layers are A.metamorphic. B.older than the sedimentary layers. C.younger than the sedimentary layers. D.the same age as the layers. The Rock Record—Relative Dating CHECK YOUR NEIGHBOR

11. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The embedded rocks (inclusions) in the sedimentary layers are A.metamorphic. B.older than the sedimentary layers. C.younger than the sedimentary layers. D.the same age as the layers. The Rock Record—Relative Dating CHECK YOUR ANSWER

12. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Uncomformities Gaps in the rock record are called uncomformities. An angular unconformity happens when tilted or folded rock is covered by younger, horizontal rock.

13. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Radiometric Dating Radiometric dating gives the actual age of a rock by measuring the ratio of radioactive isotopes to their daughter products. Half-life—the time it takes for half of the parent isotopes to decay to their daughter products.

14. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Radiometric dating can give the actual age of a rock. An exception to the “actual age” can be found in A.sedimentary and some metamorphic rocks. B.igneous rocks. C.metamorphic rocks. D.sedimentary rocks. Radiometric Dating CHECK YOUR NEIGHBOR

15. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Radiometric dating can give the actual age of a rock. An exception to the “actual age” can be found in A.sedimentary and some metamorphic rocks. B.igneous rocks. C.metamorphic rocks. D.sedimentary rocks. Explanation: In a sedimentary rock, the age of individual minerals can be determined but not the age of when the sedimentary rock formed. In a mineral reheated by metamorphism, the “time clock” is reset, complicating estimation of the rock’s age. The date obtained will be the date of the metamorphic event, not the original age of the mineral. Radiometric Dating CHECK YOUR ANSWER

16. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Geologic Time The geologic time scale—a “calendar” of Earth history. Originally created using relative dates Specific dates using radiometric dating Subdivides geologic history into units —Eons, eras, periods, and —epochs based on changes —in life forms

17. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Precambrian Time The Precambrian ranges from 4.5 billion years ago to ~543 million years ago. ~90% of Earth’s history Considerable volcanic activity Meteorite bombardment Cyanobacteria Soft-bodied organisms Primitive atmosphere and ocean Beginnings of lithospheric plate formation and movement

18. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Precambrian Time Precambrian fossils: Most common are stromatolites —Material deposited by algae —Microfossils of bacteria and algae —Importance of cyanobacteria Plant fossils—middle Precambrian Primitive animal fossils—late Precambrian Diverse and multicelled organisms existed by the close of the Precambrian

19. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Precambrian Time: Transformation of Earth’s Atmosphere First atmosphere—primarily hydrogen and helium Second atmosphere: Volcanic outgassing and cometary impacts Rich in CO 2 and H 2 O, no free oxygen H 2 O condensed to form oceans Third atmosphere: Removal of CO 2 to rocks Nitrogen increase Oxygen increase (photosynthesis) Development of O 3

20. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The development of free oxygen was crucial to the emergence of life on Earth, because it led to the formation of A.air for animals to breathe. B.ozone, O 3, which helped screen Earth from harmful incoming UV radiation. C.ozone, O 3, which primitive organisms could breathe. D.the oceans, where life emerged. Precambrian Time: Transformation of Earth’s Atmosphere CHECK YOUR NEIGHBOR

21. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The development of free oxygen was crucial to the emergence of life on Earth, because it led to the formation of A.air for animals to breathe. B.ozone, O 3, which helped screen Earth from harmful incoming UV radiation. C.ozone, O 3, which primitive organisms could breathe. D.the oceans, where life emerged. Precambrian Time: Transformation of Earth’s Atmosphere CHECK YOUR ANSWER

22. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The evolution of cyanobacteria helped oxygen escape to the atmosphere by A.keeping the carbon and expelling the oxygen. B.photosynthesis. C.releasing it from carbon dioxide. D.All of the above. Precambrian Time: Transformation of Earth’s Atmosphere CHECK YOUR NEIGHBOR

23. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The evolution of cyanobacteria helped oxygen escape to the atmosphere by A.keeping the carbon and expelling the oxygen. B.photosynthesis. C.releasing it from carbon dioxide. D.All of the above. Precambrian Time: Transformation of Earth’s Atmosphere CHECK YOUR ANSWER

24. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Paleozoic Era Spans ~300 million years. Six periods Each period was characterized by changes in life forms and tectonics. Characterized by rise and fall of sea level. Shallow seas covered the continents. Marine life flourished. Changing sea levels contributed to diversification of life forms. Hard-bodied organisms.

25. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Cambrian Period—543 to 490 Ma The “Cambrian explosion”—great diversity of life forms evolved during this time. Hard-bodied organisms: —Ability of organisms to secrete calcium carbonate and calcium phosphate for formation of an outer skeleton.

26. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Ordovician Period—490 to 443 Ma Abundant and diverse marine life: Emergence of vertebrates (e.g., jawless fishes) Surge in rate of extinctions Many landmasses on journey to become southern continent of Gondwanaland: Situated close to South Pole Widespread glaciation Sea level drops and shallow-water invertebrates deprived of habitat

27. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Silurian Period—443 to 417 Ma Supercontinent of Gondwanaland near South Pole Ancestral North America and Europe begin convergence and are situated near equator Terrestrial life—plants, scorpions, and millipedes

28. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Devonian Period—417 to 354 Ma Gondwanaland completely formed in Southern Hemisphere North America and Eurasia joined as continent of Laurasia in Northern Hemisphere Devonian known as “age of fishes” Two groups of bony fishes: —Lung fish —Lobe-finned fish, which evolved to become the amphibians

29. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Carboniferous Period—354 to 290 Ma Warm moist climate Dense swamplands Present-day coal beds Insects Amniote egg Collision of Gondwanaland with Laurasia Appalachian Mountains Ural Mountains

30. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Permian Period—290 to 248 Ma Amniote vertebrates continue to diversify Ancestral link to reptiles and mammals Permian extinction ~95% of all marine species ~70% of all land species Possible causes of extinction Redistribution of water and land Changes in landmass elevations Climate change Lowering of sea levels

31. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Paleozoic experienced several fluctuations in sea level. When sea level rises, A.shallow seas cover the continents. B.more water is tied up in glaciers making the climate colder. C.the climate turns warmer, and swamps form. D.ocean basins become shallow. The Paleozoic Era CHECK YOUR NEIGHBOR

32. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Paleozoic experienced several fluctuations in sea level. When sea level rises, A.shallow seas cover the continents. B.more water is tied up in glaciers making the climate colder. C.the climate turns warmer, and swamps form. D.ocean basins become shallow. The Paleozoic Era CHECK YOUR ANSWER

33. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley At the end of the Permian Period, sea level lowered. The lowering of sea level could be a result of A.glaciation as Pangaea drifted near the South Pole. B.the collision of Gondwanaland and Laurussia to form Pangaea. C.tectonics and climate change. D.all of the above. The Paleozoic Era CHECK YOUR NEIGHBOR

34. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley At the end of the Permian period, sea level lowered. The lowering of sea level could be a result of A.glaciation as Pangaea drifted near the South Pole. B.the collision of Gondwanaland and Laurussia to form Pangaea. C.tectonics and climate change. D.all of the above. The Paleozoic Era CHECK YOUR ANSWER

35. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Mesozoic Era Mesozoic era spans ~180 million years from 248 Ma to about 65 Ma Three Periods Triassic, Jurassic, Cretaceous Often called the “age of reptiles”

36. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Mesozoic Era Mesozoic history: Begins with much of the world’s land above sea level Seas invade western North America Breakup of Pangaea begins forming the Atlantic Ocean Subduction of oceanic crust produced widespread deformation, volcanism, and mountain building along the Western coast Mountains of western North America began forming

37. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Mesozoic Era Mesozoic life Survivors of the great Paleozoic extinction: True pines and redwoods Flowering plants Insects Reptiles (first true terrestrial animals) readily adapt to the dry Mesozoic climate

38. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Mesozoic Era Mesozoic life: Dinosaurs dominated. One group of reptiles led to the birds. Many reptile groups, along with many other animal groups, become extinct at the close of the Mesozoic. —One hypothesis is that a large asteroid or comet struck Earth. —Another possibility is that extensive volcanism occurred.

39. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The breakup of Pangaea was the greatest tectonic event in the Mesozoic. Of all the continental unions that existed in Paleozoic time, which one survived to this day? A.Africa and Asia B.The United States and Mexico C.Asia and India D.Europe and Asia The Mesozoic Era CHECK YOUR NEIGHBOR

40. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The breakup of Pangaea was the greatest tectonic event in the Mesozoic. Of all the continental unions that existed in Paleozoic time, which one survived to this day? A.Africa and Asia B.The United States and Mexico C.Asia and India D.Europe and Asia Comment: Asia and India came together in the Cenozoic, producing the Himalayas. The Mesozoic Era CHECK YOUR ANSWER

41. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Cenozoic Era Cenozoic—a smaller fraction of geologic time than the Paleozoic or Mesozoic 65 million years ago to the present Often called the “age of mammals” Pangaea’s breakup complete Two Periods: Tertiary Quaternary

42. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Cenozoic Era North America and Greenland split from Europe. Alps and Himalayas formed by collisions of land masses. Ridge formation and plate movement led to San Andreas Fault.

43. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Cenozoic Era Climates cooled Glaciation in temperate zones One-third of the land covered by ice Marine mammals and large land animals evolved Humans evolved

44. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Glaciation during the Cenozoic resulted in A.lowering of sea level worldwide. B.carving of the Swiss Alps. C.land bridge connections between various continents. D.all of the above. The Cenozoic Era CHECK YOUR NEIGHBOR

45. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Glaciation during the Cenozoic resulted in A.lowering of sea level worldwide. B.Carving of the Swiss Alps. C.land bridge connections between various continents. D.all of the above. The Cenozoic Era CHECK YOUR ANSWER

46. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Which of the following is the Cenozoic era NOT noted for? A.the debut of humans. B.ice ages. C.swampy conditions that later developed fossil fuels D.great mountain building activity. E.the San Andreas Fault. The Cenozoic Era CHECK YOUR NEIGHBOR

47. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley Which of the following is the Cenozoic era NOT noted for? A.the debut of humans. B.ice ages. C.swampy conditions that later developed fossil fuels. D.great mountain building activity. E.the San Andreas Fault. The Cenozoic Era CHECK YOUR ANSWER