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# Relative and absolute dating

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### Relative and absolute dating

1. 1. IV. Relative Dating
2. 2. Relative dating tells us the sequence in which events occurred, not how long ago they occurred. Chronological order - relational
3. 3. a. Law of Superposition The law of superposition states that in an undeformed, undisturbed sequence of sedimentary rocks, each bed is older than the one above it and younger than the one below it.
4. 4. Undistrubed Rock Layer
5. 5. A Record of Uplift, Erosion, and Deposition
6. 6. Distrubed Rock Layer
7. 7. Animation
8. 8. b. Original Horizontality The principle of original horizontality means that layers of sediment are generally deposited in a horizontal position. Draw it out!
9. 9. c. Index fossils • Index fossils are used to determine approximate age. Index fossils are widespread geographically, are limited to a short span of geologic time, and occur in large numbers. FOUND IN SEDIMENTARY ROCKS
10. 10. Index Fossils
11. 11. d. Geological Column Geologic column is an ideal sequence of rock layers that contains all the known fossils and rock formations on Earth arranged from oldest to youngest.
12. 12. Draw it out!
13. 13. V. Absolute Dating
14. 14. Absolute Dating – • the process of establishing the age of an object by determining the number of years it has existed. • It’s the most precise. It gives an actual number to the age
15. 15. A. Radioactivity  Radioactivity - the spontaneous decay of certain unstable atomic nuclei
16. 16. 1. Half - life  A half-life is the amount of time necessary for one-half of the nuclei in a sample (parent) to decay to a stable isotope (daughter).
17. 17.  Radiocarbon dating is the method for determining age by comparing the amount of carbon-14 to the amount of carbon-12 in a sample. 1. When an organism dies, the amount of carbon-14 it contains gradually decreases as it decays. 2. By comparing the ratio of carbon14 to carbon-12 in a sample, radiocarbon dates can be determined. B. Carbon-14
18. 18. Radioactive atom has an unstable nucleus that decays a. Radiation is given off b. Decay is at a constant rate c. Decay material is formed d. Half-life is the amount of time for ½ of the radioactive element to decay