In 1907, the American chemist Bertram Boltwood demonstrated that he could determine the age of a rock containing uranium-238 and thereby proved to the scientific community that radioactive dating was a reliable method.
Uranium-238, whose half-life is 4.5 billion years, transmutes into lead-206, a stable end-product.
There are several methods of determining the actual or relative age of the earth's crust: examination of fossil remains of plants and animals, relating the magnetic field of ancient days to the current magnetic field of the earth, and examination of artifacts from past civilizations.
However, one of the most widely used and accepted method is radioactive dating.
All radioactive dating is based on the fact that a radioactive substance, through its characteristic disintegration, eventually transmutes into a stable nuclide.When the rate of decay of a radioactive substance is known, the age of a specimen can be determined from the relative proportions of the remaining radioactive material and the product of its decay.