2. There are different ways geologists can describe the age of rocks & geologic events:

3. Relative Dating

4. There are different ways geologists can describe the age of rocks & geologic events: Relative Dating – when a geologist tries to put events into a chronological order -

5. There are different ways geologists can describe the age of rocks & geologic events: Relative Dating – when a geologist tries to put events into a chronological order – tries to find their relative ages.

6. There are different ways geologists can describe the age of rocks & geologic events: Relative Dating – when a geologist tries to put events into a chronological order – tries to find their relative ages. (their ages compared to other events).

7. There are different ways geologists can describe the age of rocks & geologic events: Relative Dating – when a geologist tries to put events into a chronological order – tries to find their relative ages. (their ages compared to other events). Sedimentary rock was formed…

8. There are different ways geologists can describe the age of rocks & geologic events: Relative Dating – when a geologist tries to put events into a chronological order – tries to find their relative ages. (their ages compared to other events). Sedimentary rock was formed… …then faulting occurred.

9. There are different ways geologists can describe the age of rocks & geologic events: Relative Dating – when a geologist tries to put events into a chronological order – tries to find their relative ages. (their ages compared to other events). Absolute Dating

10. There are different ways geologists can describe the age of rocks & geologic events: Relative Dating – when a geologist tries to put events into a chronological order – tries to find their relative ages. (their ages compared to other events). Absolute Dating – finding the actual age of the rock or event (in years).

11. There are different ways geologists can describe the age of rocks & geologic events: Relative Dating – when a geologist tries to put events into a chronological order – tries to find their relative ages. (their ages compared to other events). Absolute Dating – finding the actual age of the rock or event (in years). 165 m. y. old

12. There are different ways geologists can describe the age of rocks & geologic events: Relative Dating – when a geologist tries to put events into a chronological order – tries to find their relative ages. (their ages compared to other events). Absolute Dating – finding the actual age of the rock or event (in years). 165 m. y. old 50 m. y. ago

13. Question: How can we know what happened 50 million years ago?

14. Answer: We can’t KNOW, but we can make very educated guesses (inferences).

15. Question: How can we know what happened 50 million years ago? Answer: We can’t KNOW, but we can make very educated guesses (inferences). Inferences are based on the principle of uniformitarianism.

16. Question: How can we know what happened 50 million years ago? Answer: We can’t KNOW, but we can make very educated guesses (inferences). Inferences are based on the principle of uniformitarianism: The forces at work on the earth have not changed with time.

17. Question: How can we know what happened 50 million years ago? Answer: We can’t KNOW, but we can make very educated guesses (inferences). Inferences are based on the principle of uniformitarianism: The forces at work on the earth have not changed with time. (E.g. rates of erosion or sedimentation haven’t changed.)

18. Other assumptions: Principle of superposition -

19. Other assumptions: Principle of superposition – undisturbed sedimentary rock layers are youngest on top. Oldest youngest

20. Other assumptions: Principle of superposition – undisturbed sedimentary rock layers are youngest on top. Igneous intrusions & extrusions are younger than the rocks they cut through… Youngest rock

21. Other assumptions: Principle of superposition – undisturbed sedimentary rock layers are youngest on top. Igneous intrusions & extrusions are younger than the rocks they cut through… and so are the metamorphic rocks that are made by contact. Youngest rock

22. Other assumptions: Principle of superposition – undisturbed sedimentary rock layers are youngest on top. Igneous intrusions & extrusions are younger than the rocks they cut through, and so are the metamorphic rocks that are made by contact. Structural features (faults, joints, folds) occur after the rock they are in has formed.

24. Xenoliths (pieces of rock broken off and carried by magma) are older than the igneous rock they are stuck in. xenoliths

25. Correlation is a way of showing rocks or events in different locations are the same age:

26. “Walking the outcrop” – following the actual rocks.

27. Similarity of rock – direct similarities between layers of rock in different locations

28. Fossils –

29. Fossils – remains of old dead stuff. mastadont trilobite Grebdnilosaur

30. Fossils – When a shellfish dies and falls to the seabed, its soft parts quickly rot away, to leave just the hard shell. This soon becomes buried under sand and mud. Over millions and millions of years, water trickles through the mud, dissolving the shell away, to leave a hole, called a mold. Minerals in the water may take the place of the shell, hardening to form a cast of the shell. So a fossil may be either a cast or a mold. This series of events rarely happens on land, so fossils of sea creatures are more common than those of land animals.

31. Fossils – remains of old dead stuff. Index Fossils – cover a wide region, but lived for a short period of time.

32. Fossils – remains of old dead stuff. Index Fossils – cover a wide region, but lived for a short period of time. They are very helpful in identifying the ages of rocks and other unknown fossils. Gosiuthichthys – 48 my old Sandstone – 48 my old

33. These trilobites are 375 m.y. old.

34. These trilobites are 362 m.y. old.

35. These trilobites are 375 m.y. old. These trilobites are 362 m.y. old. How old can these spirifers be?

36. Volcanic Time Markers (“key beds”) - rapid deposition of igneous material over large areas.

37. What does the rock record suggest about geologic history?

38. 1.Fossil evidence and rock records give us an overall geologic history of an area.

39. What does the rock record suggest about geologic history? 1.Fossil evidence and rock records give us an overall geologic history of an area. 2. Buried erosional surfaces (“unconformities”) indicate gaps in the rock record. Erosion destroyed the rock record.

40. What does the rock record suggest about geologic history? 1.Fossil evidence and rock records give us an overall geologic history of an area. 2. Buried erosional surfaces (“unconformities”) indicate gaps in the rock record. Erosion destroyed the rock record. 3. Based on fossil evidence, geologic time is divided into large main units (“eras”).

41. Each era represents a time of a different dominant life form (or no life forms).

42. (See Reference Tables for details.)

43. Each era represents a time of a different dominant life form (or no life forms). (See Reference Tables for details.) For example, find out when the following creatures existed: mucrospirifer coelophysis eurypterus phacops

44. Each era represents a time of a different dominant life form (or no life forms). (See Reference Tables for details.) For example, find out when the following creatures existed: mucrospirifer coelophysis eurypterus phacops What’s special about eurypterus?

45. Each era represents a time of a different dominant life form (or no life forms). (See Reference Tables for details.) For example, find out when the following creatures existed: mucrospirifer coelophysis eurypterus phacops What’s special about eurypterus? For what periods does NYS have no rock record?

46. Each era represents a time of a different dominant life form (or no life forms). (See Reference Tables for details.) Cenozoic Era has the mammals.

47. Each era represents a time of a different dominant life form (or no life forms). (See Reference Tables for details.) Cenozoic Era has the mammals. Mesozoic Era had the dinosaurs.

48. Each era represents a time of a different dominant life form (or no life forms). (See Reference Tables for details.) Cenozoic Era has the mammals. Mesozoic Era had the dinosaurs. Paleozoic Era had the trilobites

49. Each era represents a time of a different dominant life form (or no life forms). (See Reference Tables for details.) Cenozoic Era has the mammals. Mesozoic Era had the dinosaurs. Paleozoic Era had the trilobites Precambrian had none for a very long time, and then soft-bodied organisms.

51. How can geologists measure the absolute age of rock and fossils?

52. Radiometric Dating - using the natural breakdown of radioactive elements to determine the age of rocks.

53. How can geologists measure the absolute age of rock and fossils? Radiometric Dating - using the natural breakdown of radioactive elements to determine the age of rocks. Some atoms (“mother isotopes”) are radioactive; they have nuclei that are unstable and decay

54. How can geologists measure the absolute age of rock and fossils? Radiometric Dating - using the natural breakdown of radioactive elements to determine the age of rocks. Some atoms (“mother isotopes”) are radioactive; they have nuclei that are unstable and decay (lose protons, neutrons or energy) to become other, more stable atoms

55. How can geologists measure the absolute age of rock and fossils? Radiometric Dating - using the natural breakdown of radioactive elements to determine the age of rocks. Some atoms (“mother isotopes”) are radioactive; they have nuclei that are unstable and decay (lose protons, neutrons or energy) to become other, more stable atoms (“daughter isotopes”).

56. How can geologists measure the absolute age of rock and fossils? Radiometric Dating - using the natural breakdown of radioactive elements to determine the age of rocks. Some atoms (“mother isotopes”) are radioactive; they have nuclei that are unstable and decay (lose protons, neutrons or energy) to become other, more stable atoms (“daughter isotopes”). The decay is random, natural and unaffected by external forces

57. How can geologists measure the absolute age of rock and fossils? Radiometric Dating - using the natural breakdown of radioactive elements to determine the age of rocks. Some atoms (“mother isotopes”) are radioactive; they have nuclei that are unstable and decay (lose protons, neutrons or energy) to become other, more stable atoms (“daughter isotopes”). The decay is random, natural and unaffected by external forces (heat, pressure, chem. reactions).

58. Radioactive decay is also a secondary energy source for Earth.

59. There is a specific decay rate for each radioactive element,

60. Radioactive decay is also a secondary energy source for Earth. There is a specific decay rate for each radioactive element, which makes the time needed to fully breakdown predictable.

61. Radioactive decay is also a secondary energy source for Earth. There is a specific decay rate for each radioactive element, which makes the time needed to fully breakdown predictable. Half – Life

62. Radioactive decay is also a secondary energy source for Earth. There is a specific decay rate for each radioactive element, which makes the time needed to fully breakdown predictable. Half – Life is the time it takes for half of a mother isotope to decay into a daughter isotope.

63. Radioactive decay is also a secondary energy source for Earth. There is a specific decay rate for each radioactive element, which makes the time needed to fully breakdown predictable. Half – Life is the time it takes for half of a mother isotope to turn into a daughter isotope. Eg. C-14 becomes N-14 in 5700 years

64. Radioactive decay is also a secondary energy source for Earth. There is a specific decay rate for each radioactive element, which makes the time needed to fully breakdown predictable. Half – Life is the time it takes for half of a mother isotope to turn into a daughter isotope. Eg. C-14 becomes N-14 in 5700 years K-40 becomes Ar-40 in 1.3 b. y.

65. A fossil is found to have 25% of its original Carbon – 14. How old is the fossil?

66. Start with 100% C-14.

67. A fossil is found to have 25% of its original Carbon – 14. How old is the fossil? Start with 100% C-14. After one half life (5700 yr.) 50% remains.

68. A fossil is found to have 25% of its original Carbon – 14. How old is the fossil? Start with 100% C-14. After one half-life (5700 yr.) 50% remains. After two half-lives (11400 yr) 25% remains

69. A fossil is found to have 25% of its original Carbon – 14. How old is the fossil? Start with 100% C-14. After one half-life (5700 yr.) 50% remains. After two half-lives (11400 yr) 25% remains In cases where we try to date remains of living things, we look for

70. A fossil is found to have 25% of its original Carbon – 14. How old is the fossil? Start with 100% C-14. After one half-life (5700 yr.) 50% remains. After two half-lives (11400 yr) 25% remains In cases where we try to date remains of living things, we look for Carbon-14.

71. A fossil is found to have 25% of its original Carbon – 14. How old is the fossil? Start with 100% C-14. After one half-life (5700 yr.) 50% remains. After two half-lives (11400 yr) 25% remains In cases where we try to date remains of living things, we look for Carbon-14. The problem is that C-14 doesn’t last very long,

72. A fossil is found to have 25% of its original Carbon – 14. How old is the fossil? Start with 100% C-14. After one half-life (5700 yr.) 50% remains. After two half-lives (11400 yr) 25% remains In cases where we try to date remains of living things, we look for Carbon-14. The problem is that C-14 doesn’t last very long, so for fossils over 70,000 yr old we use other isotopes.

73. What does the rock/fossil record suggest?

74. 1.A great variety of organisms once lived on Earth.

75. What does the rock/fossil record suggest? 1.A great variety of organisms once lived on Earth. Most are now extinct.

76. 2.They lived in a great variety of environmental conditions.

77. 3.Life forms appear to have started as simple organisms and became increasingly complex.

78. 2.They lived in a great variety of environmental conditions. 3.Life forms appear to have started as simple organisms and became increasingly complex. An oversimplified look at evolution of life forms.

79. 2.They lived in a great variety of environmental conditions. 3.Life forms appear to have started as simple organisms and became increasingly complex. 4.Variations in organisms have been observed, which suggests evolutionary development.