The Rock Record

1. The Rock Record Chapter 8 Mr. Sierra's Earth Science

2. p.185 itarianism Uniform • A principle that geologic processes that occurred in the past can be explained by current geologic processes. • Volcanism and Erosion

3. p.186 Relative Age • The age of an object in relation to the age of other objects

4. p.187 Law of Superposition • The law that a sedimentary rock layer is older than the layers above it and younger than the layers below it if the layers are not disturbed. Newest Oldest

5. Unities p.189 conform • A break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time.

6. Absolute Age • The numeric age of an object or event, often stated in years before the present. • Using a process like “radiometric dating” or “carbon dating”

7. Rates of Deposition • In general, about 30 cm of sedimentary rock are deposited over a period of 1,000 years. • However, a flood can deposit many meters of sediment in just one day.

8. Radiometric Dating • A method of determining the absolute age of an object by comparing the relative percentages of a radioactive (parent) and a stable (daughter) isotope. • Half-Life: the time required for half of a sample of a radioactive isotope to break down.

9. Carbon-14 Dating • Plants absorb Carbon during Photosynthesis • Scientists compare the carbon isotopes 12C and 14C(radioactive) • This can be used to determine the ages of wood, bones, shells and other organic remains that areless than 7,000 years old.

10. Paleontology • The scientific study of fossils.

11. Trace Fossils • Fossilized evidence of past movement of an animal such as tracks, footprints, borings and borrows.

12. Index Fossils • A fossil that is used to establish the age of rock layers because it is: • Distinct – features different from other fossils • Abundant – occurs in fairly large numbers • Widespread – present in scattered rocks • Existed only for a short span of geologic time