Potassium-argon (K-Ar) dating is a radiometric technique used to determine the age of rocks and minerals. It relies on the radioactive decay of potassium-40 (K-40) to argon-40 (Ar-40). Potassium-40 is a naturally occurring isotope of potassium, and over time, it decays into argon-40, a stable gas. Since argon is a gas, it can escape from minerals when they are heated or formed, so the amount of argon-40 present in a mineral is used to estimate the time since the mineral last cooled or crystallized.
The process works like this:
- Potassium-40 decays to argon-40 at a known rate (its half-life is about 1.3 billion years).
- By measuring the ratio of potassium to argon in a sample, scientists can calculate how much time has passed since the rock or mineral last cooled and trapped argon within it.
When is it used?
Potassium-argon dating is primarily used for dating volcanic rocks and minerals, particularly when they are older than 100,000 years, since the method is effective for very old samples. It’s commonly used in:
- Dating volcanic rocks: To establish the age of volcanic eruptions.
- Dating ancient rock formations: Useful in studying the age of earth’s crust and ancient geological processes.
- Dating early hominid fossils: In some cases, when associated with volcanic layers, it can help establish the age of fossils found in these strata.
It’s particularly useful for dating materials that are millions or even billions of years old, such as rocks from volcanic eruptions or minerals from early Earth.