To measure the rate of decay, a suitable detector records the number of beta particles ejected from a measured quantity of carbon over a period of time, say a month (for illustration purposes).Since each beta particle represents one decayed carbon-14 atom, we know how many carbon-14 atoms decayed during that month.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.The difference in the number of sand grains represents the number of carbon-14 atoms that have decayed back to nitrogen-14 since the mammoth died. The sand grains in the top bowl fall to the bottom bowl to measure the passage of time.Because we have measured the rate at which the sand grains fall (the radiocarbon decay rate), we can then calculate how long it took those carbon-14 atoms to decay, which is how long ago the mammoth died. If all the sand grains are in the top bowl, then it takes exactly an hour for them all to fall.
If we know what fraction of the carbon atoms are radioactive, we can also calculate how many radiocarbon atoms are in the lump.Through photosynthesis carbon dioxide enters plants and algae, bringing radiocarbon into the food chain.Radiocarbon then enters animals as they consume the plants (figure 2).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).
So even we humans are radioactive because of trace amounts of radiocarbon in our bodies.