less than 1 minute read

Dating Techniques

Potassium-argon Dating



When volcanic rocks are heated to extremely high temperatures, they release any argon gas trapped in them. As the rocks cool, argon-40 (40Ar) begins to accumulate. Argon-40 is formed in the rocks by the radioactive decay of potassium-40 (40K). The amount of 40Ar formed is proportional to the decay rate (half-life) of 40K, which is 1.3 billion years. In other words, it takes 1.3 billions years for half of the 40K originally present to be converted into 40Ar. This method is generally only applicable to rocks greater than three million years old, although with sensitive instruments, rocks several hundred thousand years old may be dated. The reason such old material is required is that it takes a very long time to accumulate enough 40Ar to be measured accurately. Potassium-argon dating has been used to date volcanic layers above and below fossils and artifacts in east Africa.




Additional topics

Science EncyclopediaScience & Philosophy: Cyanohydrins to Departments of philosophy:Dating Techniques - Stratigraphy, Seriation, Faunal Dating, Pollen Dating (palynology), Amino Acid Racimization, Cation-ratio Dating - Relative dating, Absolute dating, Radioactive decay dating