Rubidium strontium dating half life

The ratio of calcium formed to argon formed is fixed and known.

Therefore the amount of argon formed provides a direct measurement of the amount of potassium-40 present in the specimen when it was originally formed.

(Note that this does not mean that the ratios are the same everywhere on earth.At the same time, the fraction of strontium-87 increases from zero and approaches 100% with increasing number of half-lives.The two curves cross each other at half life = 1.00.The number of protons in the nucleus of an atom is called its atomic number.The sum of protons plus neutrons is the mass number.