Half life age dating
The half-lives of several radioactive isotopes are known and are used often to figure out the age of newly found fossils.Different isotopes have different half-lives and sometimes more than one present isotope can be used to get an even more specific age of a fossil.The best radioactive element to use to date human fossils is Carbon-14.There are several reasons why, but the main reasons is that Carbon-14 is a naturally occurring isotope in all forms of life and its half-life is about 5730 years, so we are able to use it to date more "recent" forms of life relative to the Geologic Time Scale.
For nonliving substances, scientists use other isotopes, such as potassium-40.
Plants absorb C-14 during photosynthesis, so C-14 is incorporated into the cellular structure of plants.
Plants are then eaten by animals, making C-14 a part of the cellular structure of all living things.
The rule is that a sample is safe when its radioactivity has dropped below detection limits. So, if radioactive iodine-131 (which has a half-life of 8 days) is injected into the body to treat thyroid cancer, it’ll be “gone” in 10 half-lives, or 80 days.
This stuff is important to know when using radioactive isotopes as medical tracers, which are taken into the body to allow doctors to trace a pathway or find a blockage, or in cancer treatments.