For this article, we will use Carbon-14 as an example to illustrate how radiometric dating works. Please see the article “What is Carbon-14?” to help understand where this element comes from. Radiometric dating is the process of dating the age of rocks and fossils by measuring the amount of radioactive decay found within the specimen. Decay refers to the “parent” (Carbon-14) decaying to the “daughter” (Nitrogen-14). The decay process continues until it becomes a stabilized element. Scientists measure the specimen’s ratio of parent-to-daughter.
After an animal dies, it will no longer receive Carbon-14 into its body. As already mentioned, radioactive elements decay. Carbon-14 decays to 50% of its initial amount over the span of 5,730 years. In other words, if you find a fossil today, it will contain “X” amount of Carbon-14, but in 5,730 years (the half-life), 50% of the Carbon-14 will decay back into Nitrogen (remember that Nitrogen was the starting element that became radioactive). When radiometric dating is used on a fossil, scientists are looking for the ratio of remaining Carbon-14 to Carbon-12 (C-12 never leaves the fossil).
At the time of the animal’s death, there are one trillion Carbon-12 atoms for every one Carbon-14 atom. After the half-life, there will be two trillion C-12 atoms for every one C-14 atom because half of the C-14 had decayed. After another half-life (5,730 years), there will be four-trillion C-12 atoms for every one C-14 atom, and only 25% of the initial amount of C-14 will be left. This process continues exponentially, and after so many half-lives, there is not enough Carbon-14 left to perform an accurate measurement. The scientist then adds the number of half-lives, multiplies that sum times the length of the half-life, and that equals the age of the fossil.
Carbon-14 dating can only be reliable for up to 80,000 years. That is why other dating methods such as Uranium-Lead; Thorium-Lead; Rubidium-Strontium; Potassium-Argon; Potassium-Calcium, and a list of others are used to measure ages. A similar process is used for dating with these chemicals. It should be added that dinosaur bones, which are supposedly 65 million years old, still have Carbon-14 in them, but Carbon-14 should have decayed long ago!
Radiometric dating sounds like a valid process to date things, but there are flaws in the method.