Most radioactive isotopes have short half-lives and lose their radioactivity within a few days or years.
There are some that have longer half-lives; they are used to determine the age of materials on the geologic scale.
(2) Remember earth is estimated to be well over 4.5 billion years old.(1) The lore of fossils is attributed to its link to dinosaurs.However, fossils are much older than the age of the dinosaurs.By carefully cataloging their observations of which fossils were found in which rocks, these men and other geologists were able to confer that rocks of the same age could be found on either side of the English Channel."Smith and others knew that the succession of life forms preserved as fossils is useful for understanding how and when the rocks formed.They have since been revised but his accomplishments were on the correct track.Radioactive decay is a spontaneous process in which an isotope (the parent) loses particles from its nucleus to form an isotope of a new element (the daughter).The radiometric scale is a more recent development borrowed from the physical sciences and applied to geologic problems.The ability to use radioactive elements to date the materials that exist in the composition of rocks is due to the discovery of the natural radioactive decay of uranium in 1896 by Henry Becquerel, the French physicist.Followed shortly thereafter by Professor Boltwood in 1907, a radiochemist of Yale University, who applied the idea of using radioactivity to approximate the ages of ancient particles, rocks, and fossils.Professor Boltwood published the first list of geologic ages based on radioactivity.