Which quantity helps determine the absolute age of rocks and fossils? (1 point)
O the ratio of protons to neutrons in carbon-14
• the ratio of carbon-12 to carbon-14
• the difference between the number of protons and neutrons in carbon-14
• the difference between the amounts of carbon-12 and carbon-14
• the difference between the amounts of carbon-12 and carbon-14
The quantity that helps determine the absolute age of rocks and fossils is the ratio of carbon-12 to carbon-14. Carbon-14 is an isotope of carbon that is commonly used in the process of radiometric dating. It decays over time, so by measuring the ratio of carbon-12 (a stable isotope) to carbon-14 in a sample, scientists can estimate how long it has been since the organism died.
To determine the absolute age using this method, scientists compare the ratio of carbon-12 to carbon-14 in a sample with the known ratio in living organisms. Since organisms take in carbon during their lifetime, the ratio of carbon-12 to carbon-14 is relatively constant. However, once an organism dies, it no longer takes in carbon, and the carbon-14 in its remains gradually decays. By measuring the current ratio of carbon-12 to carbon-14, scientists can calculate how many half-lives have passed since the organism died, and hence determine its absolute age.