Half life radioactive dating
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.
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.
In the field of nondestructive testing radiographers (people who produce radiographs to inspect objects) also use half-life information.
After another 86 minutes, half of the 5 grams of Barium-139 would decay into Lanthanum-139; you would now have 2.5 grams of Barium-139 and 7.5 grams of Lanthanum-139.
Below is a chart of commonly used radiometric isotopes, their half-lives, and the daughter isotopes they decay into.
Let's say you found a fossil you think to be a human skeleton.
Scientists can use the half-life of Carbon-14 to determine the approximate age of organic objects less than 40,000 years old.
By determining how much of the carbon-14 has transmutated, scientist can calculate and estimate the age of a substance. Isotopes with longer half-lives such as Uranium-238 can be used to date even older objects.
This is what your readout said, so your fossil has undergone two half-lives.