Which of the following is not a useful ratio in determining the age of rocks or sediments?

• A. Potassium-argon
• B. Uranium-Lead
• C. Silica - Carbon
• D. Rubidium-Strontium

Answer: (C)

Dating hinges on a parent–daughter radioactive decay pair with a known half-life. The ratio of parent to daughter in a mineral records how many half-lives have passed since the system formed, provided the system stayed closed.

Potassium-argon, uranium–lead, and rubidium–strontium are all classic radiometric pairs because they involve a radioactive parent that decays to a measurable daughter within minerals that can retain the products over geological timescales. The silica–carbon pairing isn’t a radiometric dating pair. Silicon has no practical, long-lived radioactive decay scheme used for rock ages, and carbon dating relies on carbon-14 in organic material or specific carbon-bearing contexts—not on a general silica–carbon ratio in rocks. Therefore, silica–carbon isn’t a reliable dating method for rocks or sediments.