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Unformatted text preview: Geology 101 Lab Final Study Guide Lab 8: Geologic Time: What is the difference between a relative and absolute age? +Relative Age:- We establish a relative time scale for the rocks and events in the area of the cross section. - This method gives us no idea of how many years of Earth history are represented, for we have no numerical dates. Nor do we know how this area compares to any other. +Absolute Age:- Radiometric Dating: - The procedure of calculating the absolute age of rocks and minerals that contain certain radioactive isotopes. +What is a Half-Life?-The time required for half of the nuclei in a sample to decay is called a half-life of an isotope (50 percent).-If the half-life of a radioactive isotope is known and the parent/daughter ratio can be determined, the age of the sample can be calculated. +Know how to calculate the age of a crystal (or organic matter) given the % remaining of parent radioactive isotope. +What types of rocks (igneous, sedimentary, or metamorphic) are good for radiometric dating, which arent? - Rubidium-87, Thorium-232, and the two isotopes of Uranium are used only for dating rocks that are millions of years old, but Potassium-40 is more versatile. - +Why? Understand the assumptions (i.e. what can mess up a radiometric date?) Relative Dating: - Rocks and structures are placed in their proper sequence or order. Only the chronological order of events is determined. Law of Original Horizontality: - Strata is deposited horizontally if it is not horizontal, then something must have happened after deposition.- Sedimentary layers and lava flows were deposited in relatively flat sheets. Law of Lateral Continuity: - Strata extends in all directions unless something is there to stop it. Ex. Fault.- Layers extend in all directions until they thin to nothing or are truncated by a fault. Law of Superposition: - In any undeformed sequence of sedimentary rocks, each bed is older than the one above and younger than the one below. - The oldest layer is at the bottom of a sequence and the youngest layer is at the top. Law of Inclusions:- Inclusion is older than the rock they are included in.- Any piece of rock must be older than the rock pr sediment into which it has been incorporated....
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- Fall '08