How can scientists measure the age of fossils or other objects using radioactivity?

How can scientists measure the age of fossils or other objects using radioactivity? Why is it that radioactive chemicals, or radioisotopes, can be safely injected into a person for diagnostic purposes with no lingering effects? Why is there so much concern about where people discard radioactive wastes? These questions can all relate to radioactive half-lives, or the time required for a given radioactive sample to lose half of its radioactivity. Small quantities of natural radioactivity exist in the environment in part due to the constant bombardment from outer space of cosmic rays. This continually creates small amounts of radioactive carbon and other radioisotopes which are incorporated in carbon-containing compounds, such as carbon dioxide used in photosynthesis, which then becomes part of glucose, which can be eaten by an animal, and on through the food web. As long as living organisms are absorbing substances from their environment by breathing, drinking, or eating, they absorb this radioactivity, much of which becomes part of the organism’s body. Once dead, obviously no more is absorbed, so whatever was there will slowly, over time, undergo radioactive decay. Eventually, no radioactivity will remain. However, that can take many millions of years for some types of radioactivity. (Some radioisotopes, such as those used for medical diagnoses, decay quite rapidly — a matter of microseconds — so after a few minutes, virtually no radioactivity remains. Unfortunately, many radioactive wastes decay very slowly, making it difficult to find safe repositories that will contain them for, say, thousands of years. By comparing the ratio of radioisotopes to non-radioactive isotopes, the amount of time that has passed for a given sample can be calculated.

In this lab, you will simulate radioactive decay, make a half-life curve, and use it to make some predictions.