relative-and-absolute-dating_earth-science.pptx

relative and absolute dating

1. Fossil Dating

2. Relative and Absolute Dating

3. HOW DO WE KNOW THE AGE OF FOSSILS? Scientists use 2 methods to determine the age of fossils: 1. Relative Dating 2. Absolute Dating

4. Relative and Absolute Dating

5. What is Dating? When geologists date rocks, they are determining how long ago they formed. Two ways to do this: Relative Dating Absolute Dating

6. Relative Dating Determining how old something is compared to something else Use words like “ older ” or “ younger ” instead of exact numbers

7. I. Relative Dating Relative Dating is when you give the age of a rock or fossil compared to another rock or fossil. Example: Rock A is OLDER than Rock B. An actual age in years is not determined.

8. Relative Dating

9. II. Rules of Relative Dating Law of Superposition : When sedimentary rock layers are deposited, younger layers are on top of older deposits.

10. Rules of Relative Dating 2. Law of Original Horizontality : Sedimentary rock layers are deposited horizontally. If they are tilted, folded, or broken, it happened later.

11. Rules of Relative Dating 3. Law of Cross-Cutting Relationships : If an igneous intrusion or a fault cuts through existing rocks, the intrusion/fault is YOUNGER than the rock it cuts through

12. Order these layers from oldest to youngest Youngest layer Oldest layer

13. Order the events from oldest to youngest Fault Gray Layer Multicolored layer Spotted Layer OLDEST LAYER/EVENT YOUNGEST LAYER/EVENT

14. III. Correlation Rock layers in different places can be correlated or matched up by matching up the rocks and fossils in the layers.

15. IV. Unconformity When rock has been eroded , so you have a missing section of time in the rock record.

16. Unconformity

17. Why are some of the layers tilted? What happened to the top of the folded rocks? The missing rock layers is called an __________.

18. What type of rocks formed above? What events might have caused the rock layers to become tilted? Why is the top flat? What caused the angular unconformity?

19. Index Fossils Some species of organisms only lived for a short period of time before they became extinct . If you use radiometric dating to get an age for the fossil, then you know that the rock the fossil is found in is also that age. Trilobite: Index fossil for the Paleozoic Era Age: 590-250 mya

20. Graptolite Index Fossil of the Ordovician Period Age: 500-335 mya

21. Fossil B lived 10 million years ago – 2 million years ago. Fossil A lived 20 million years ago- 8 million years ago. What do you know about the age of the rock containing both fossils?

22. http://reynolds.asu.edu/glg103/relative_age_principles.htm

23. What is “B”? Place the layers in order from oldest to youngest

24. Put the events in order

25. Put the events in order

26. Youngest _____ _____ _____ _____ _____ _____ Oldest

27. Youngest_____ _____ _____ _____ _____ _____Oldest

28. Youngest ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ Oldest

29. Youngest ____ ____ ____ ____ ____ ____ ____ ____ _____ _____ Oldest

30. Make your own Strata Sequence Requirements: One of each: Igneous intrusion, faulting, folding, erosion Each rock type needs the correct symbol Neatness – use a ruler Key for rock types Separate Answer key

31. Absolute Dating Determining how old something is Use numbers (in millions of years, mya) Only works for Igneous Rocks

32. Absolute Dating Determines the specific age of a fossil Looks at chemical properties 2 types: Carbon-14 (radiocarbon) Potassium-Argon

33. Carbon-14 Dating Also known as Radiocarbon dating Used to date organic substances Scientists measure the radiocarbon in the fossil to determine its age Can only date specimens up to about 60,000 years old

34. Potassium-Argon Dating Scientists determine the age of the rock surrounding the fossil to determine the fossil’s age. Used only for inorganic substances (rocks and minerals) Scientists measure the amount of argon in the rock to determine its age Dates rock 60,000 years old and older

35. How Absolute Dating Works When magma/lava cools, radioactive elements are incorporated into the minerals Examples: -- Potassium 40 -- Uranium 235

36. How Absolute Dating Works These elements begin to decay at a known rate starting when the rock cools We can measure how much of the element is left Tells us how much time has passed since the rock formed.

37. What can we learn from this?  T-Rex Fossil  Geologist Basalt, dated to 80 mya Basalt flow, dated to 100 mya Sandstone So when did this T-Rex live? Between 100 and 80 mya This may not seem very accurate, but compared to the 4,500 million years the earth has been around it gives us a lot more information than we had before

38. What can we learn from this? Absolute Dating Helps us determine the age of the earth Helps us determine when specific events in the history of the earth happened (ex. Extinction of the dinosaurs) Relative Dating Can help us estimate the time span between major earthquakes, storms, tsunamis etc Can help us determine the order that life forms developed on earth

39. QUIZ

40. Which rock layer is the oldest? Youngest? Oldest Youngest

41. If you wanted to figure out the exact age of a rock, what technique would you use? Relative Dating Carbon-14 Dating Law of Superposition Potassium-Argon Dating

42. If you were looking to find the exact age of a fossil that is at least 1 million years old, what technique would you use? a. Carbon-14 Dating b. Potassium-Argon Dating c. Relative Dating d. You can’t; it is impossible

43. If you wanted to figure out the exact age of a fossil that is less than 40,000 years old, what technique would you use? a. Carbon-14 Dating b. Potassium-Argon Dating c. Relative Dating d. You can’t; it is impossible