Why are unstable isotopes useful for dating rocks

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After all, a dinosaur wouldn’t be caught dead next to a trilobite.The narrower a range of time that an animal lived, the better it is as an index of a specific time.If a rock has been partially melted, or otherwise metamorphosed, that causes complications for radiometric (absolute) age dating as well.

Look for “absolute” ages such as cornerstones, dates carved into fresh concrete, or dates stamped on manhole covers.No bones about it, fossils are important age markers.But the most accurate forms of absolute age dating are radiometric methods. Sedimentary rocks in particular are notoriously radioactive-free zones.Radioactive isotopes decay at a known rate, and have a predictable half life; the time it will take for half of a given quantity of radioactive isotope to decay into a stable state.Using these known numbers, it is possible to estimate the relative age of an object..

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