Which dating method is used to determine the age of very old rocks and minerals by isotopic decay, such as potassium-argon dating?

Which dating method is used to determine the age of very old rocks and minerals by isotopic decay, such as potassium-argon dating?

• A. Relative dating: superposition
• B. Absolute dating: carbon dating
• C. Absolute dating: potassium-argon (K-Ar) dating
• D. Relative dating: fossil succession

Answer: (C)

Isotopic decay provides a clock because certain unstable isotopes decay at a fixed rate over time. When a rock forms, minerals that contain potassium-40 can trap the argon-40 produced as it decays. Over the ages, more argon-40 accumulates while some potassium-40 remains. By measuring how much argon-40 is present compared with how much potassium-40 is left, scientists calculate how long this process has been occurring, giving an actual age for the rock. This approach is a form of absolute dating and is ideal for very old rocks because potassium-40 has a long half-life, allowing the clock to run over hundreds of millions to billions of years. In contrast, carbon dating works for organic material and only up to about 50,000 years, and relative dating methods like superposition or fossil succession tell only which rocks are older or younger, not their actual ages. So potassium-argon dating is the technique suited for determining ages of very old rocks and minerals by isotopic decay.

Isotopic decay provides a clock because certain unstable isotopes decay at a fixed rate over time. When a rock forms, minerals that contain potassium-40 can trap the argon-40 produced as it decays. Over the ages, more argon-40 accumulates while some potassium-40 remains. By measuring how much argon-40 is present compared with how much potassium-40 is left, scientists calculate how long this process has been occurring, giving an actual age for the rock. This approach is a form of absolute dating and is ideal for very old rocks because potassium-40 has a long half-life, allowing the clock to run over hundreds of millions to billions of years. In contrast, carbon dating works for organic material and only up to about 50,000 years, and relative dating methods like superposition or fossil succession tell only which rocks are older or younger, not their actual ages. So potassium-argon dating is the technique suited for determining ages of very old rocks and minerals by isotopic decay.