Changes
The mathematical formula that is used to figure the age of the rock depends on the [[half-life]] of potassium-40 (the time it takes for half the potassium-40 in a given sample to decay). The half-live of potassium-40 is approximately 1.26 billion years (that is, 1.26x10<sup>9</sup> years).
Obviously, this formula depends on the laws of physics remaining constant over time. If the rate of [[radioactive decay]] has changed over time, the formula will not give correct dates. Most scientists believe that the rate of potassium-argon decay has not changed over the history of the earth. However, some creationists have argued that God increased the rate of potassium-argon decay during the first few days of Creation, thus causing the potassium-argon dating method to give erroneously old date readings.{{fact}}
Other isotopes with shorter half-lives can also be used to date objects- however, each method has its own drawbacks. For instance, the decay of carbon-14 is often used to complement the potassium-argon dating of [[dinosaur]] [[fossils]].
