With the discovery of radiometric dating, it became possible for the first time to attempt precise figures.Radiometric dating works on the principle that certain atoms and isotopes are unstable.Even in the case of very long half-lives, modern scientific instruments are now accurate enough to give very fine readings.
so geological dating is usually done by looking for pairs of elements bound in the rocks. Geological dating requires isotopes with longer half lives than carbon-14 has.It also requires other things, such as that the elements involved do not wash away in water or escape as gas in an unknown manner.However, the error range increases drastically once you pass 50,000 years.Also, it is of little use in anything more recent than 5,000 years ago.Fortunately, we are able to date older fossils using the radiometric breakdown of other elements (Potassium-Argon dating, Argon-Argon dating, and Rubidium dating [I'm writing this without any refs - so this last one might be wrong]).Usually the radioactive 'clocks' for these elements are started when the elements are deposited by a volcanic eruption (usually in the form of ash).(The item being tested must be organic based, and must be dead - tests on live mollusks showed an age of 2000 years).If a fossil is completely replaced (permineralized), then it would be useless in a similar test - because it no longer is organic.they can emit alpha partices, or beta particles, or pure energy called gamma rays. It is not radio active If suppose one neutron is added then it becomes an isotope P-32.This is radio active Same way right from P-31 if one neutron is taken out then P-30 would result. These isotopes are said to be radio active isotopes.