Classroom presentations to accompany Understanding Earth , 3rd edition

1. Classroom presentations to accompany Understanding Earth, 3rd edition prepared by Peter Copeland and William Dupré University of Houston Chapter 9 The Rock Record and the Geologic Timescale

2. Geologic Time William E. Ferguson

3. Geologic Time A major difference between geologists and most other scientists is their attitude about time. A "long" time may not be important unless it is > 1 million years.

4. Two ways to date geologic events 1) relative dating (fossils, structure) 2) absolute dating (isotopic, tree rings, etc.)

5. Amount of Time Required for Some Geologic Processes and Events Fig. 9.1

6. Some geologic processes can be documented using historical records(brown is new land from 1887-1988) Fig. 9.2

7. Ammonite Fossils Petrified Wood Chip Clark Fig. 9.4 Tom Bean

8. Steno's Laws Nicolaus Steno (1669) • Principle of Superposition • Principle of Original Horizontality • Principle of Lateral Continuity Laws apply to both sedimentary and volcanic rocks.

9. Principle of Superposition In a sequence of undisturbed layered rocks, the oldest rocks are on the bottom.

10. Principle of Superposition Youngest rocks Oldest rocks Fig. 9.3b Jim Steinberg/Photo Researchers

11. Principle of Original Horizontality Layered strata are deposited horizontal or nearly horizontal or nearly parallel to the Earth’s surface.

12. Principles of original horizontality and superposition Fig. 9.3a

13. Principle of Lateral Continuity Layered rocks are deposited in continuous contact.

14. Principle of Lateral Continuity Mapview

15. Principle of Lateral Continuity Map view

16. Principle of Lateral Continuity Map view

17. Using Fossils to Correlate Rocks Fig. 9.5

18. Unconformity A buried surface of erosion

19. Sedimentation of Beds A-D Beneath the Sea Fig. 9.6

20. Uplift and Exposure of D to Erosion Fig. 9.6

21. Continued Erosion Removes D and Exposes C to Erosion Fig. 9.6

22. Subsidence and Sedimentation of E over C Unconformity: a buried surface of erosion Fig. 9.6

23. Formation of a Disconformity Fig. 9.6

24. The Great Unconformity of the Grand Canyon Fig. 9.7 Geoscience Features Picture Libraryc

25. Angular unconformity, Grand Canyon

26. South rim of the Grand Canyon

27. South rim of the Grand Canyon 250 million years old Paleozoic Strata 550 million years old 1.7 billion years old Precambrian

28. South rim of the Grand Canyon 250 million years old 550 million years old 1.7 billion years old Nonconformity

29. Nonconformity in the Grand Canyon

30. Nonconformity in the Grand Canyon Tapeats Sandstone (~550 million years old) Vishnu Schist (~1700 million years old)

31. Sedimentation of Beds A-D Beneath the Sea Fig. 9.8

32. Deformation and Erosion During Mountain Building Fig. 9.8

33. Erosional Surface Cuts Across Deformed Rocks Fig. 9.8

34. Subsidence and Subsequent Deposition Buries Erosional Surface Angular Unconformity Fig. 9.8

35. Formation of an Angular Unconformity Fig. 9.8

36. Cross-cutting Relationships Fig. 9.9

37. Fig. 9.10 Schlumberger Executive Communications

38. Sequence A forms during lower sea level Fig. 9.11a

39. Sequence B forms during higher sea level Fig. 9.11b

40. Reconstructing Relative Sequence of Events Fig. 9.12

41. Generalized Stratigraphic Section of Rocks Exposed in the Grand Canyon after: Beus & Moral (1990)

42. Some of the Geologic Units Exposed in the Grand Canyon Michael Collier

43. The Geologic time scale • Divisions in the worldwide stratigraphic column based on variations in preserved fossils • Built using a combination of stratigraphic relationships, cross-cutting relationships, and absolute (isotopic) ages

44. The Geologic Time Scale Fig. 9.13

45. Absolute geochronology • Add numbers to the stratigraphic column based on fossils. • Based on the regular radioactive decay of some chemical elements.

46. Isotopes Different forms of the same element containing the same number of protons, but varying numbers of neutrons. i.e.: 235U, 238U 87Sr, 86Sr 14C, 12C

47. Radioactive Decay of Rubidium to Strontium Fig. 9.14

48. Half-life The half-life of a radioactive isotope is defined as the time required for half of it to decay.

49. Proportion of Parent Atoms Remaining as a Function of Time Fig. 9.15

50. Isotopic dating • Radioactive elements (parents) decay to nonradioactive (stable) elements (daughters). • The rate at which this decay occurs is constant and knowable. • Therefore, if we know the rate of decay and the amount present of parent and daughter, we can calculate how long this reaction has been proceeding.