Final answer:
Potassium-argon dating can date igneous and metamorphic rocks up to 4.3 billion years old, using the decay of K-40 into Ar-40. Other methods like rubidium-strontium and uranium-lead dating are used for varying ranges and materials, helping to estimate the earth's age and understand geological history.
Step-by-step explanation:
Potassium-argon dating can be used to directly date igneous and metamorphic rocks as old as 4.3 billion years. This method relies on the decay of radioactive potassium-40 (K-40) into stable argon-40 (Ar-40). K-40 decays with a half-life of 1.25 billion years, which makes it a useful tool for dating very old geological materials. By crushing a rock sample and measuring the escaped Ar-40 gas, scientists can determine the Ar-40:K-40 ratio and thus calculate the age of the rock. This dating technique assumes that no argon gas was originally present in the rock when it solidified, which is generally the case for deep geological formations.
Other dating methods, like rubidium-strontium dating and uranium-lead dating, work on similar principles but are used for different age ranges and types of materials. For example, uranium-lead dating has been used to determine the age of the oldest known rocks on Earth, the Jack Hills zircons, which are almost 4.4 billion years old. These methods are crucial for scientists to estimate the lower age limit of the Earth itself, as well as to understand geological time scales and the history of our planet.