It is one of the simplest examples of a differential equation.Geologist Ralph Harvey and historian Mott Greene explain the principles of radiometric dating and its application in determining the age of Earth.Since there is now only 1/4 of the original amount of Parentium-123, we know that two half-lives of Parentium-123 have elapsed.

...igneous activity (both extrusive and intrusive) occurred in the Caledonian mountain belt, which stretched from New England, Nova Scotia, Newfoundland, Scotland, and Scandinavia to eastern Greenland.If the mineral contained 1 part per million Parentium-123 and 3 parts per million Daughterium-123, we could be sure all the Daughterium-123 was originally Parentium-123.In other words there was originally 4 parts per million Parentium-123 and 0 parts per million Daughterium-123.Analyzing specimens whose relative geologic ages were known, Boltwood found that the ratio of lead to uranium did indeed increase...Scientific knowledge of Earth’s geologic history has advanced significantly since the development of radiometric dating, a method of age determination based on the principle that radioactive atoms in geologic materials decay at constant, known rates to daughter atoms.If one knows how much of this radioactive material was present initially in the object (by determining how much of the material has decayed), and one knows the half-life of the material, one can deduce the age of the object.Imagine we have an undiscovered element, Parentium, that has a radioactive isotope, Parentium-123, which decays to stable Daughterium-123.