Article / Updated 03-26-2016
Scientists estimate that the Earth is about 4.5 billion years old, based on radioisotope dating techniques. To understand how this process works, you need to know a little bit about atoms and isotopes. Often, any one atom has several different forms, called isotopes. Atoms are made up of electrons, protons, and neutrons, and the number of electrons and protons determines the type of atom.