Question

Geochronologists rely on distinct isotopic systems to date ancient materials, choosing methods based on the composition and age of the sample. Radiocarbon dating determines the age of organic remains by measuring the ratio of unstable carbon-14 to stable carbon-12. This carbon is absorbed by living organisms from the atmosphere, and the measurement directly tracks the progressive loss of the radioactive isotope over time. Because of carbon-14’s relatively brief half-life of 5,730 years, this technique is precise only for materials under 50,000 years old, and it is entirely restricted to organic substances. In contrast, potassium-argon (K-Ar) dating measures the accumulation of gaseous argon-40, which is the decay product of radioactive potassium-40 found in volcanic minerals. Instead of measuring the depletion of a biological isotope, K-Ar dating measures the ratio of the parent isotope to the trapped daughter gas within solidified rock, a process initiated only when volcanic rock cools. With a half-life of 1.25 billion years, K-Ar dating is suited only for inorganic samples older than 100,000 years.

According to the passage, which of the following statements explicitly describes a difference between the mechanisms of radiocarbon dating and potassium-argon (K-Ar) dating?