The illustration below shows the three isotopes of carbon.Some isotopes of certain elements are unstable; they can spontaneously change into another kind of atom in a process called “radioactive decay.” Since this process presently happens at a known measured rate, scientists attempt to use it like a “clock” to tell how long ago a rock or fossil formed.It cannot be used directly to date rocks; however, it can potentially be used to put time constraints on some inorganic material such as diamonds (diamonds could contain carbon-14). Cosmic rays from outer space, which contain high levels of energy, bombard the earth’s upper atmosphere.These cosmic rays collide with atoms in the atmosphere and can cause them to come apart.The atomic number corresponds to the number of protons in an atom.Atomic mass is a combination of the number of protons and neutrons in the nucleus.
If the starting assumption is false, all the calculations based on that assumption might be correct but still give a wrong conclusion. Libby’s original work, he noted that the atmosphere did not appear to be in equilibrium. Libby since he believed the world was billions of years old and enough time had passed to achieve equilibrium. Libby’s calculations showed that if the earth started with no If the cosmic radiation has remained at its present intensity for 20,000 or 30,000 years, and if the carbon reservoir has not changed appreciably in this time, then there exists at the present time a complete balance between the rate of disintegration of radiocarbon atoms and the rate of assimilation of new radiocarbon atoms for all material in the life-cycle.2C in the atmosphere.So, a carbon atom might have six neutrons, or seven, or possibly eight—but it would always have six protons.An “isotope” is any of several different forms of an element, each having different numbers of neutrons.Note that, contrary to a popular misconception, carbon dating is not used to date rocks at millions of years old.Before we get into the details of how radiometric dating methods are used, we need to review some preliminary concepts from chemistry.Recall that atoms are the basic building blocks of matter.