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USGS CMG InfoBank: Determining the Age of Rocks

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Comment: 22:16 - 23:19 (01:03)
Source: Annenberg/CPB Resources - Earth Revealed - 10. Geologic Time
Keywords: "geologic age", mineralogy, mineral, element, isotope, "mass spectrometer", "isotopic ratio", "absolute age dating"

Our transcription: The first step in determining the age of the rock is finding the proper rock in the field and determining its mineralogy.
Once we've determined what it is we want to date, then we sample it in the field, bring it back into the laboratory, separate out the minerals that we want to date, that tell us the age of the rock.
Once we have a clean mineral separate, then we take it into the laboratory, and we separate out chemically the elements that are within the rock that have the isotopic system that we're interested in.
And then once we have the elements separated, we bring the elements into the mass spectrometer and with the mass spectrometer we analyze the isotopes of the elements that we're interested in.
And it's the isotopic ratios between the parent and the daughter isotopes and between the various daughter isotopes, that give us the age of the rock.

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