Which dating method measures potassium converting to argon?

• A. Dendrochronology
• B. Potassium-argon dating
• C. Radiocarbon dating
• D. Thermoluminescence

Answer: (B)

Potassium-argon dating relies on the radioactive decay of potassium-40 to argon-40. As minerals form, some of the argon produced by this decay can become trapped inside the crystal. Over time, argon-40 accumulates in proportion to how much potassium-40 remains. By measuring the ratio of potassium-40 to argon-40 in a sample, scientists determine how long it has been since the rock crystallized. This method is especially useful for dating ancient volcanic rocks and ash layers, where the solidified rock has trapped the argon gas. The dating relies on a closed system—argon must not escape since formation—otherwise the measured ratio would be misleading. Radiometric dating methods like this are chosen when the material contains enough potassium and has remained sealed; other dating methods, such as radiocarbon dating for organic materials, dendrochronology from tree rings, or thermoluminescence from trapped electrons, use different processes and materials.