Uncovering Earth's History: Rock, Fossil Record & Dating Methods

1. 6th Grade Science Chapter 3- The Rock & Fossil Record

2. Formula • °C  x  9/5 + 32 = °F • (°F  -  32)  x  5/9 = °C • Examples • 1)  Convert 37°C to Fahrenheit. • 37°C x  9/5 + 32 = 98.6°F • OR • 37°C x 9 + 32 = 98.6°F  5 • 2)  Convert 98.6°F to Celsius. • (98.6°F  -  32)  x  5/9 = 37°C • OR • (98.6°F - 32) x 5 = 37°C  • 9

3. “The present is the key to the past.”-James Hutton What Do You Think? We study the past because if we don’t, we are doomed to repeat it. But how can studying the present help us understand earth’s history? What are some processes you can see today that also occurred millions of years ago?

4. Earth’s Story & Those Who Listened • “The present is the key to the past.” • Father of modern geology James Hutton 1726-1797

5. Earth’s Story & Those Who Listened • Hutton knew that Hadrian’s wall was built by the Romans in historical times Hadrian’s Wall, England

6. Earth’s Story & Those Who Listened • Only 1600 years old, the wall was already starting to weather and erode Hadrian’s Wall, England

7. Earth’s Story & Those Who Listened • Hutton wondered how long it would take to erode a mountain Arthur’s Seat Volcano, Edinburgh, Scotland

8. Earth’s Story & Those Who Listened • Hutton decided that it would take millions of years, making the earth very ancient Arthur’s Seat Volcano, Edinburgh, Scotland

9. Earth’s Story & Those Who Listened • Hutton realized that erosion and deposition have been going on for a long time Arthur’s Seat Volcano, Edinburgh, Scotland

10. Earth’s Story & Those Who Listened • In 1788, James Hutton • wrote: • Theory of the Earth • (a collection of his notes) notes)

11. Earth’s Story & Those Who Listened • In his book he described: • Uniformitarianism • It is the idea that the same geologic processes shaping the Earth today have been at work throughout Earth’s history. James Hutton 1726-1797

12. Earth’s Story & Those Who Listened • Hutton’s views of a billion-year-old earth clashed with most scientists’ belief in catastrophism James Hutton 1726-1797

13. Earth’s Story & Those Who Listened • Most scientists supported catastrophism. It is the idea that all geologic change happens quickly

14. Earth’s Story & Those Who Listened • These scientists used huge floods, eruptions, and other catastrophes to explain rapid geologic change

15. Earth’s Story & Those Who Listened • Catastrophism was a guiding principle for decades. • Only after the work of Charles Lyell did people consider uniformitarism. • 1830-1833 Lyell published 3 volumes in: • Principles of Geology • In it, he stated that change happened gradually.

16. Earth’s Story & Those Who Listened • Today, scientists think that sudden events are the cause of some changes in earth’s past

17. Earth’s Story & Those Who Listened • But they agree that the earth is old, and that most change is gradual

18. Earth’s Story and Those Who First Listened Today’s Scientists realize that neither of these principles: uniformitarianism nor catastrophism account for all geologic changes. Most change is gradual, but catastrophes have occurred throughout Earth’s history.

19. Earth’s Story and Those Who First Listened paleontology-science involved with the study of past life paleontologist-a scientist who studies past life What data do they study? Fossils

20. Earth’s Story and Those Who First Listened fossils-the remains of organisms preserved by geologic processes Invertebrate paleontologist-studies animals without backbones Vertebrate Paleontologist-studies animals with backbones

21. Relative Dating: Which came first? What Do You Think? Suppose your friend piles his stuff on his floor and never cleans his room. Under the top layer of clothes, you find a pizza box. Under this is a bunch of CDs then some homework and under this is a ham sandwich. Arrange these four layers from oldest to youngest…

22. Relative Dating: Which came first? relative dating-determining whether an object or event is older or younger than other objects or events

23. Relative Dating: Which came first? • The Principle of Superposition states that younger rocks lie over older rocks Grand Canyon

24. Relative Dating: Which came first? • The Principle of Superposition is used to find the relative ages of rock layers Grand Canyon

25. Relative Dating: Which came first? • Geologists can use rock layers from many locations to create a geologic column James Hutton 1726-1797

26. Relative Dating: Which came first? • The geologic column is an ideal sequence of rock layers that contains all known rock formations and fossils on Earth

27. Relative Dating: Which came first?

28. Relative Dating: Which came first? • The dike is the youngest feature, because the other layers were cut by it

29. Relative Dating: Which came first? Look at page 66 Figure 3 Terms: fault-a break in the Earth’s crust along which blocks of the crust slide relative to on another intrusion-molten rock from the Earth’s interior that squeezes into existing rock and cools

30. Relative Dating: Which came first? folding-occurs when rock layers bend and buckle from Earth’s internal forces tilting-occurs when internal forces in the Earth slant rock layers These features are younger than the rock layers because the rock layers had to be present before the features could cut across them.

31. Relative Dating: Which came first? • The Law of Cross-Cutting Relationships can tell geologists the relative age of a fault or intrusion

32. Relative Dating: Which came first? • Use your knowledge to order the layers, faults and intrusions in the next slide from oldest to youngest

33. Relative Dating: Which came first?

34. Relative Dating: Which came first? • If rock layers are not horizontal, something must have disturbed them after they formed.

35. Relative Dating: Which came first? • An unconformity is a surface that represents a missing part of the geologic column Hutton’s Unconformity

36. Relative Dating: Which came first? • Most unconformities form by erosion and nondeposition.

37. Relative Dating: Which came first? Types of unconformities: • disconformities-are found where part of a sequence of parallel rock is missing. This is the most common type.

38. Formation of an Unconformity • Sediment is eroded from a hill and deposited in a valley 30-15 Million Years Ago

39. Formation of an Unconformity • The area is uplifted and exposed to erosion, then theland surface is eroded away 15-5 Million Years Ago

40. Formation of an Unconformity • Deposition resumes • Can you spot the unconformity? 5 Million Years Ago- Present

41. Relative Dating: Which came first? • nonconformities-are found where horizontal sedimentary rock layers lie on top of an eroded surface of older intrusive igneous or metamorphic rock

42. Relative Dating: Which came first? • angular unconformities-are found between horizontal layers of sedimentary rock and layers of rock that have been tilted or folded.

43. Section 3: Absolute Dating • Absolute dating-the process of establishing the age of an object by determining the number of years it has existed

44. How is this done? • element-a substance that cannot be separated or broken down into simpler substances by chemical means • atom-the smallest unit of an element that maintains the properties of that element • isotope-atoms of the same element that have the same number of protons but a different number of neutrons

45. An atom is made of protons, neutrons, and electrons.

46. Rules • In a stable atom, protons and electrons are equal.

47. Radioactive-this is what scientists call unstable isotopes Radioactive decay-a process where radioactive isotopes tend to break down into stable isotopes of the same or other elements

48. Radioactive Decay Parent Isotope Daughter Isotope Radioactive Decay When some unstable isotopes decay a neutron is converted into a proton. An electron is released Unstable Isotope 6 protons, 8 neutrons Stable Isotope 7 protons, 7 neutrons

49. What does this show you? • Scientists can use it to determine an object’s age (like rocks or fossils)

50. How is this done? • parent isotope-the unstable radioactive isotope • daughter isotope-the stable isotope that is produced by the radioactive decay of the parent isotope