Final answer:
K-Ar dating is used to date geological samples like igneous and metamorphic rocks. It measures the decay of K-40 to Ar-40 to determine the age of rocks, useful for rocks older than about 100,000 years and can estimate the earth's age.
Step-by-step explanation:
Potassium-argon (K-Ar) dating is a radiometric technique used to establish the age of geological materials. This method is highly useful in the kind of environment where igneous and metamorphic rocks occur, as it determines the time since these rock samples last cooled to a temperature at which the argon could no longer escape the lattice structure of the minerals within the rock.
K-40, a naturally occurring isotope, decays to form Ar-40 with a half-life of 1.25 billion years. To determine the age of a rock using K-Ar dating, scientists crush the rock sample and measure the escaped Ar-40 gas. By analyzing the ratio of Ar-40 to K-40, they can calculate the time elapsed since the rock solidified. The precision of K-Ar dating generally falls within a few percent of the sample's true age, assuming no argon has been lost or gained since the rock was formed.
K-Ar dating is particularly useful for dating volcanic rocks and can provide dates for the oldest known terrestrial rocks and by extension, the age of the earth. However, it's not suitable for dating rocks younger than about 100,000 years or the bones of living organisms, for which other dating methods, like carbon-14 dating, would be more appropriate.