Hewitt/Lyons/Suchocki/Yeh Conceptual Integrated Science

1. Hewitt/Lyons/Suchocki/YehConceptual Integrated Science Chapter 26 EARTH’S HISTORY

2. This lecture will help you understand: • History of Earth Science • How the rock record reveals Earth’s history • The methods used to determine rocks’ age • The construction of the geologic time scale • The evolution of Earth’s atmosphere • How life evolved through time • Plate tectonics and its role in evolution • When and how different mountains formed

3. A Model of Earth’s History • Earth is ~4.5 billion years old. • Compared to a single calendar year: • Formation of Earth Jan. 1 • Oldest rocks Feb. 26 • Bacterial life Mar. 23 • Dinosaurs Dec. 14 to 26 • Homo sapiens Dec. 31 @11:50 pm • Human history Dec. 31 @11:59 pm

4. A Model of Earth’s History • Geologic Time—from Earth’s formation to the present. • This history is recorded in the rocks of Earth’s crust.

5. Uniformitarianism vs. Catastrophism Catastrophism—Earth’s present state is the result of sudden, short-lived, violent events. • Implies a young Earth (creation ~4000 BC) Uniformitarianism—Earth is the result of slow processes over long periods of time. • Implies an old Earth (~4.5 billion years), dynamic and everchanging.

6. Earth’s History The most fundamental principle in geology is Uniformitarianism: The present is the key to the past. The processes and laws (physics, chemistry, biology, etc.) that operate today are the same as those that have operated in the past.

7. The Rock Record 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

8. Principles of 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.

9. Principles of Relative Dating Inclusion: • Any inclusion is older than the rock containing it. Faunal succession: • Fossil organisms follow one another in a definite, irreversible time sequence.

10. Principles of Relative Dating CHECK YOUR NEIGHBOR Three dikes (igneous intrusion) cut into a rock body. Which dike is the oldest, and which is the youngest? • A is oldest, then B, and C is the youngest. • C is oldest, then B, and A is the youngest. • B is oldest, then A, and C is the youngest. • A is oldest, then C, and B is the youngest.

11. Principles of Relative Dating CHECK YOUR ANSWER Three dikes (igneous intrusion) cut into a rock body. Which dike is the oldest, and which is the youngest? • A is oldest, then B, and C is the youngest. • C is oldest, then B, and A is the youngest. • B is oldest, then A, and C is the youngest. • A is oldest, then C, and B is the youngest.

12. Principles of Relative Dating CHECK YOUR NEIGHBOR The embedded rocks (inclusions) in the sedimentary layers are • metamorphic. • older than the sedimentary layers. • younger than the sedimentary layers. • the same age as the layers.

13. Principles of Relative Dating CHECK YOUR ANSWER The embedded rocks (inclusions) in the sedimentary layers are • metamorphic. • older than the sedimentary layers. • younger than the sedimentary layers. • the same age as the layers.

14. 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.

15. Principles of Relative Dating CHECK YOUR NEIGHBOR Radiometric dating can give the actual age of a rock. An exception to the “actual age” can be found in • sedimentary and some metamorphic rocks. • igneous rocks. • metamorphic rocks. • sedimentary rocks.

16. Principles of Relative Dating CHECK YOUR ANSWER Radiometric dating can give the actual age of a rock. An exception to the “actual age” can be found in • sedimentary and some metamorphic rocks. • igneous rocks. • metamorphic rocks. • 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.

17. 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

18. Precambrian Time The Precambrian ranges from 4.5 billion years ago to ~542 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

19. 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

20. Transformation of Earth’s Atmosphere First atmosphere—primarily hydrogen and helium Second atmosphere: • Volcanic outgassing and cometary impacts • Rich in CO2 and H2O, no free oxygen • H2O condensed to form oceans Third atmosphere: • Removal of CO2to rocks • Nitrogen increase • Oxygen increase (photosynthesis) • Development of O3

21. Transformation of Earth’s Atmosphere CHECK YOUR NEIGHBOR The development of free oxygen was crucial to the emergence of life on Earth, because it led to the formation of • air for animals to breathe. • ozone, O3, which helped screen Earth from harmful incoming UV radiation. • ozone, O3, which primitive organisms could breathe. • the oceans, where life emerged.

22. Transformation of Earth’s Atmosphere CHECK YOUR ANSWER The development of free oxygen was crucial to the emergence of life on Earth, because it led to the formation of • air for animals to breathe. • ozone, O3, which helped screen Earth from harmful incoming UV radiation. • ozone, O3, which primitive organisms could breathe. • the oceans, where life emerged.

23. Transformation of Earth’s Atmosphere CHECK YOUR NEIGHBOR The evolution of cyanobacteria helped oxygen escape to the atmosphere by • keeping the carbon and expelling the oxygen. • photosynthesis. • releasing it from carbon dioxide. • All of the above.

24. Transformation of Earth’s Atmosphere CHECK YOUR ANSWER The evolution of cyanobacteria helped oxygen escape to the atmosphere by • keeping the carbon and expelling the oxygen. • photosynthesis. • releasing it from carbon dioxide. • All of the above.

25. Paleozoic Era Spans ~300 million years. • Six periods—Each period 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.

26. Cambrian Period—542 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.

27. Ordovician Period—490 to 443 Ma Abundant and diverse marine life: • Emergence of vertebrates (e.g., jawless fishes) Many landmasses on journey to become southern continent of Gondwanaland: • Situated close to South Pole • Widespread glaciation • Sea level drops • Shallow-water invertebrates deprived of habitat

28. Silurian Period—443 to 417 Ma Many landmasses joining together as southern continent of Gondwanaland: • Africa, South America, India, Australia, Antarctica • Situated close to South Pole Ancestral North America and Europe begin convergence and are situated near equator • Continents flooded by periodic shallow seas • Formation of many evaporite beds Terrestrial life • Plants, scorpions, and millipedes

29. Devonian Period—417 to 354 Ma Gondwanaland completely formed in Southern Hemisphere North America and Eurasia joined as continent of Laurussia 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

30. Carboniferous Period—354 to 290 Ma Warm moist climate Dense swamplands • Present-day coal beds Insects Amniote egg Collision of Gondwanaland with Laurussia • Appalachian Mountains • Ural Mountains

31. Permian Period—290 to 248 Ma Amniote vertebrates continue to diversify • Ancestral link to reptiles and mammals Permian extinction • ~90% of all marine species • ~70% of all land species Possible causes of extinction • Volcanic activity in Siberia • Blocked solar radiation • Formation of Pangaea • Lowering of sea level

32. The Paleozoic Era CHECK YOUR NEIGHBOR The Paleozoic experienced several fluctuations in sea level. When sea level rises, • shallow seas cover the continents. • more water is tied up in glaciers making the climate colder. • the climate turns warmer, and swamps form. • ocean basins become shallow.

33. The Paleozoic Era CHECK YOUR ANSWER The Paleozoic experienced several fluctuations in sea level. When sea level rises, • shallow seas cover the continents. • more water is tied up in glaciers making the climate colder. • the climate turns warmer, and swamps form. • ocean basins become shallow.

34. The Paleozoic Era CHECK YOUR NEIGHBOR At the end of the Permian, sea level lowered. The lowering of sea level could be a result of • glaciation as Pangaea drifted near the South Pole. • the collision of Gondwanaland and Laurussia to form Pangaea. • tectonics and climate change. • all of the above.

35. The Paleozoic Era CHECK YOUR ANSWER At the end of the Permian, sea level lowered. The lowering of sea level could be a result of • glaciation as Pangaea drifted near the South Pole. • the collision of Gondwanaland and Laurussia to form Pangaea. • tectonics and climate change. • all of the above.

36. 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”

37. 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 • North American plate began to override the Pacific plate • Mountains of western North America began forming

38. 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 • Reptiles have shell-covered eggs that can be laid on the land

39. 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.

40. The Mesozoic Era CHECK YOUR NEIGHBOR The breakup of Pangaea was the greatest tectonic event in the Mesozoic. Of all the continental unions that existed in Paleozoic time, only that of • Africa and Asia has survived to this day. • the United States and Mexico has survived. • Asia and India has survived to this day. • Europe and Asia has survived to this day.

41. The Mesozoic Era CHECK YOUR ANSWER The breakup of Pangaea was the greatest tectonic event in the Mesozoic. Of all the continental unions that existed in Paleozoic time, only that of • Africa and Asia has survived to this day. • the United States and Mexico has survived. • Asia and India has survived to this day. • Europe and Asia has survived to this day. Comment: Asia and India came together in the Cenozoic, producing the Himalayas.

42. 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” • Two Periods: • Tertiary • Quaternary

43. Cenozoic Era North America: Most of the continent was above sea level throughout the Cenozoic era. Western North America: • Mountain building, volcanism, and earthquakes • Large region uplifted—Basin and Range province is formed, Rockies are re-elevated, rivers erode the Grand and Black canyons, volcanic activity is abundant • San Andreas Fault

44. Cenozoic Era Eastern North America: • Stable with abundant marine sedimentation • Eroded Appalachians raised by isostatic adjustments Eurasia: • Africa–Arabia collision produces Alps • India with Asia produce the Himalayas Worldwide: • Climates cooled • Glaciation in temperate zones • One-third of the land covered by ice

45. Cenozoic Era Cenozoic life: Mammals replaced reptiles as the dominant land animals. Flowering plants dominated the plant world: • Strongly influenced the evolution of both birds and mammals • Food source for both birds and mammals

46. Cenozoic Era Cenozoic life: • Mammals diversified quite rapidly, and some groups become very large: • e.g., hornless rhinoceros, which stood nearly 16 feet high • Many large animals became extinct • Humans evolve • And dominate

47. The Cenozoic Era CHECK YOUR NEIGHBOR Glaciation during the Cenozoic resulted in • lowering of sea level worldwide. • carving of the Swiss Alps. • land bridge connections between various continents. • all of the above.

48. The Cenozoic Era CHECK YOUR ANSWER Glaciation during the Cenozoic resulted in • lowering of sea level worldwide. • Carving of the Swiss Alps. • land bridge connections between various continents. • all of the above.

49. The Cenozoic Era CHECK YOUR NEIGHBOR The Cenozoic era is noted for • the debut of humans. • ice ages. • great mountain building activity. • the San Andreas Fault. • the Hawaiian Islands. • all of the above.

50. The Cenozoic Era CHECK YOUR ANSWER The Cenozoic era is noted for • the debut of humans. • ice ages. • great mountain building activity. • the San Andreas Fault. • the Hawaiian Islands. • all of the above.