Radiometric dating equation
Radiometric dating is based on the decay of long-lived radioactive isotopes that occur naturally in rocks and minerals.
These parent isotopes decay to stable daughter isotopes at rates that can be measured experimentally and are effectively constant over time regardless of physical or chemical conditions.
Lord Kelvin and Clarence King calculated the length of time required for the Earth to cool from a white-hot liquid state; they eventually settled on 24 million years.
James Joly calculated that the Earth’s age was 89 million years on the basis of the time required for salt to accumulate in the oceans.
There were other estimates but the calculations were hotly disputed because they all were obviously flawed by uncertainties in both the initial assumptions and the data.
Unbeknownst to the scientists engaged in this controversy, however, geology was about to be profoundly affected by the same discoveries that revolutionized physics at the turn of the 20th century.
My purpose here is not to review and discuss all of the dating methods in use.
Some methods work only on closed systems, whereas others work on open systems.
There are a number of long-lived radioactive isotopes used in radiometric dating, and a variety of ways they are used to determine the ages of rocks, minerals, and organic materials.