Method of determining the age of a fossil by using radioactive half-lives.

Method of determining the age of a fossil by using radioactive half-lives.

• A. Struggle for existence
• B. Carbon dating
• C. Fossil
• D. Evolution

Answer: (B)

Dating fossils with radioactive decay hinges on how certain isotopes decay at a predictable rate. In carbon dating, the key isotope is carbon-14, which forms in the atmosphere and is taken up by living organisms. While alive, the ratio of carbon-14 to carbon-12 stays in balance with the atmosphere. After death, carbon-14 decays to nitrogen-14 with a half-life of about 5,730 years, so the amount left drops exponentially over time. By measuring how much carbon-14 remains in the fossil and comparing it to the original amount, scientists estimate how long it has been since death. This method works best for relatively recent fossils, up to roughly 50,000 years, because after that the carbon-14 becomes too scarce to measure accurately. For much older fossils, other radiometric dating methods are used, often applied to the rocks surrounding the fossil rather than the fossil itself. The other options describe broader evolutionary ideas or general fossil concepts, not a dating method.

Dating fossils with radioactive decay hinges on how certain isotopes decay at a predictable rate. In carbon dating, the key isotope is carbon-14, which forms in the atmosphere and is taken up by living organisms. While alive, the ratio of carbon-14 to carbon-12 stays in balance with the atmosphere. After death, carbon-14 decays to nitrogen-14 with a half-life of about 5,730 years, so the amount left drops exponentially over time. By measuring how much carbon-14 remains in the fossil and comparing it to the original amount, scientists estimate how long it has been since death. This method works best for relatively recent fossils, up to roughly 50,000 years, because after that the carbon-14 becomes too scarce to measure accurately. For much older fossils, other radiometric dating methods are used, often applied to the rocks surrounding the fossil rather than the fossil itself. The other options describe broader evolutionary ideas or general fossil concepts, not a dating method.