Potassium-argon dating Potassium-40 is a radioactive isotope of potassium that decays into argon-40. The half-life of potassium-40 is 1.3 billion years, far longer than that of carbon-14, allowing much older samples to be dated. K–Ar dating was used to calibrate the geomagnetic polarity time scale.

## What is the purpose of potassium-argon dating and carbon-14 dating?

Potassium-argon dating, method of determining the time of origin of rocks by measuring the ratio of radioactive argon to radioactive potassium in the rock.

## Why is potassium-argon dating used instead of carbon dating for items that are estimated to be about a million years old?

Geologists have used this method to date rocks as much as 4 billion years old. It is based on the fact that some of the radioactive isotope of Potassium, Potassium-40 (K-40) ,decays to the gas Argon as Argon-40 (Ar-40). Potassium (K) is one of the most abundant elements in the Earths crust (2.4% by mass).

## What is the difference between radioactive dating and carbon dating?

Radiocarbon dating is also simply called carbon-14 dating. Carbon-14 is a radioactive isotope of carbon, with a half-life of 5,730 years (which is very short compared with the above isotopes), and decays into nitrogen. A carbon-based life form acquires carbon during its lifetime.