Radiometric dating is a means of determining the "age" of a mineral specimen by determining the relative amounts present of certain radioactive elements. By "age" we mean the elapsed time from when the mineral specimen was formed. Radioactive elements "decay" that is, change into other elements by "half lives. The formula for the fraction remaining is one-half raised to the power given by the number of years divided by the half-life in other words raised to a power equal to the number of half-lives. If we knew the fraction of a radioactive element still remaining in a mineral, it would be a simple matter to calculate its age by the formula. To determine the fraction still remaining, we must know both the amount now present and also the amount present when the mineral was formed.

If you're seeing this message, it means we're having trouble loading external resources on our website. To log in and use all the features of Khan Academy, please enable JavaScript in your browser. Science Biology History of life on Earth Radiometric dating. Chronometric revolution.

Right now, 40, feet overhead, a cosmic ray is sending a neutron smashing into a nitrogen atom, smacking a proton out of its nucleus and forming an isotope called carbon Living things constantly consume carbon—through photosynthesis, for plants, and for animals, ingestion of those plants. The atmospheric ratio of carbon to regular carbon remains consistent at one part per trillion, so if something is alive, one-trillionth of its carbon atoms will be C But once a plant or animal dies, its carbon is no longer replenished.

If you have a fossil, you can tell how old it is by the carbon 14 dating method. This is a formula which helps you to date a fossil by its carbon. The half life of carbon 14 is years.

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