A sample starts off with all uranium and no lead. Over time, the ratio of lead to uranium increases.
How do they do it? Particle accelerator piece is from 3: Using layers of sequenced rock to find out which is older and younger Ages of events are placed in order of occurrence. Ages of events are placed in order of occurrence. No exact date is identified. Miss Miller is older than her students. My presentations Profile Feedback Log out. Auth with social network: Registration Forgot your password?
Exact Age Dating"— Presentation transcript: Download ppt "Relative Age Dating Vs. What is relative dating? OK Do First Actions: List the layers from youngest to oldest.The Right Age for Dating
About project SlidePlayer Terms of Service. How do scientists actually know these ages? Geologic age dating—assigning an age to materials—is an entire discipline of its own.
In a way this field, called geochronology, is some of the purest detective work earth scientists do. There are two basic approaches: Here is an easy-to understand analogy for your students: Absolute age dating is like saying you are 15 years old and your grandfather is 77 years old.
To determine the relative age of different rocks, geologists start with the assumption that unless something has happened, in a sequence of sedimentary rock layers, the newer rock layers will be on top of older ones. This is called the Rule of Superposition. This rule is common sense, but it serves as a powerful reference point. Geologists draw on it and other basic principles http: Relative age dating also means paying attention to crosscutting relationships.
Say for example that a volcanic dike, or a fault, cuts across several sedimentary layers, or maybe through another volcanic rock type.
Exact age dating
Pretty obvious that the dike came after the rocks it cuts through, right? With absolute age dating, you get a real age in actual years. Based on the Rule of Superposition, certain organisms clearly lived before others, during certain geologic times. The narrower a range of time that an animal lived, the better it is as an index of a specific time.
No bones about it, fossils are important age markers. But the most accurate forms of absolute age dating are radiometric methods.
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This method works because some unstable radioactive isotopes of some elements decay at a known rate into daughter products. This rate of decay is called a half-life.
Half-life simply means the amount of time it takes for half of a remaining particular isotope to decay to a daughter product. Good discussion from the US Geological Survey: So geochronolgists just measure the ratio of the remaining parent atom to the amount of daughter and voila, they know how long the molecule has been hanging out decaying. There are a couple catches, of course. Not all rocks have radioactive elements.