Different isotopes
can be used to determine the age of geologic substances such as this rock.
Radioactive decay was first discovered in uranium in 1896 by French physicist, Henry Becquerel. Atoms with large nuclei are inherently unstable and will inevitably decay and lose particles. Different elements decay at different rates. By comparing the amount of radioactive isotope that decayed to the amount of time it takes for half of the isotope to decay, scientists can accurately estimate the age of any substance. This practice is known as radiometric dating.
Instructions
Perform Radiometric Dating
1. Determine the specific isotope you want to use to measure the age of your sample. Different isotopes have different half-lives that range from seconds to billions of years. The half-life of an isotope is the amount of time it takes for half of a radioactive substance to decay. You're going to need to use an isotope with a very long half-life because of the incredible age of the Earth. According to U.S. Geological Survey, the most common isotope used to measure the age of geologic substances is potassium-40 and its decayed form, argon-40. Also, according to Carleton College, carbon-14 cannot be used in radiometric dating because its half-life is too short and can only be used to measure the age of a substance that was once living.
2. Find the half-life of the isotope you're going to use. You can refer to a variety of online sources and textbooks to find the half-lives of common isotopes used for radiometric dating. The Science Education Resource Center at Carleton College has a comprehensive list of radioactive isotopes and their half-lives.
3. Divide the natural log of 2 by the half-life of your isotope. The resulting quotient is the decay constant of your isotope.
4. Multiply the reciprocal of your decay constant by the natural log of one plus the ratio of the number of radioactive isotope atoms to the number of decayed isotope atoms. This will give you the age of your geologic substance. The equation to determine the age of your rock can be found at the U.S. Geologic Survey's website.
Tags: radiometric dating, amount time, amount time takes, Carleton College, decay constant, Different isotopes, geologic substances