# Half life dating formula

Half-life is defined as the amount of time it takes a given quantity to decrease to half of its initial value.

The term is most commonly used in relation to atoms undergoing radioactive decay, but can be used to describe other types of decay, whether exponential or not.

If we knew the fraction of a radioactive element still remaining in a mineral, it would be a simple matter to calculate its age by the formula To determine the fraction still remaining, we must know both the amount now present and also the amount present when the mineral was formed.

Carbon-14 dating: See Carbon 14 Dating in this web site.

Any argon present in a mineral containing potassium-40 must have been formed as the result of radioactive decay.

F, the fraction of K40 remaining, is equal to the amount of potassium-40 in the sample, divided by the sum of potassium-40 in the sample plus the calculated amount of potassium required to produce the amount of argon found. In spite of the fact that it is a gas, the argon is trapped in the mineral and can't escape.

Potassium-Argon dating: The element potassium (symbol K) has three nuclides, K39, K40, and K41. K40 can decay in two different ways: it can break down into either calcium or argon.

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