The age of fossils can sometimes be determined by radiometric dating, which is based on the constant rate of decay of radioactive isotopes. the time required for half of a radioactive isotope to decay is called the half-life of that isotope. for example, the isotope carbon-14 has a half-life of 5,730 years. suppose it is determined that a fossilized leaf contains 12.5% of the carbon-14 that was present when the fossil formed. how old is the fossil? express your answer numerically.