If we assume that the mammoth originally had the same number of carbon-14 atoms in its bones as living animals do today (estimated at one carbon-14 atom for every trillion carbon-12 atoms), then, because we also know the radiocarbon decay rate, we can calculate how long ago the mammoth died. This dating method is also similar to the principle behind an hourglass (figure 4).The sand grains that originally filled the top bowl represent the carbon-14 atoms in the living mammoth just before it died.So if half the sand grains are in the top bowl and half in the bottom bowl, then 30 minutes has elapsed since the sand grains began falling.
The most well-known of all the radiometric dating methods is radiocarbon dating.
Although many people think radiocarbon is used to date rocks, it is limited to dating things that contain carbon and were once alive (fossils).
After all, we should be able to estimate how long ago a creature lived based on how much radiocarbon is left in its body. Radiocarbon (carbon-14) is a very unstable element that quickly changes into nitrogen.
Half the original quantity of carbon-14 will decay back to the stable element nitrogen-14 after only 5,730 years.
Since the atmosphere is composed of about 78 percent nitrogen,2 a lot of radiocarbon atoms are produced—in total about 16.5 lbs. These rapidly combine with oxygen atoms (the second most abundant element in the atmosphere, at 21 percent) to form carbon dioxide (CO This carbon dioxide, now radioactive with carbon-14, is otherwise chemically indistinguishable from the normal carbon dioxide in the atmosphere, which is slightly lighter because it contains normal carbon-12.