Which dating method uses the ratio of unstable isotopes to stable isotopes to determine the age of a rock?

• A. Relative dating
• B. Observations
• C. Absolute dating
• D. Evidence

Answer: (C)

Radiometric dating uses the changing ratio of unstable (parent) isotopes to stable (daughter) isotopes to determine a rock’s age. Over time, parent atoms decay at a predictable rate known as the half-life. By measuring how much parent and how much daughter are present in the rock, scientists can calculate how long it has been since the rock formed. This provides a numerical age in years, which is why it’s categorized as absolute dating.

Relative dating, in contrast, tells you the order of events or which rocks are older or younger but doesn’t give an exact age. Observations and evidence are general terms and not dating methods themselves, so they don’t yield precise ages.