A radioactive isotope of the element potassium decays to produce argon. If the ratio of argon to potassium is found to be 7:1, how many half-lives have occurred? A. 1 half-lifeB. 3 half-livesC. 7 half-livesD. 8 half-lives

The answer is Option B, 3 half-lives.

Explanation:

Potassium-argon dating (K-Ar dating) is a radiometric dating method. It measures the radioactive decay of an isotope of potassium (K) into argon (Ar). Potassium is a common element found in many materials like clay and certain minerals. The technique is best suited to dating minerals and rocks more than 100,000 years old. For shorter timescales, it is unlikely that enough argon (40 Ar) will have accumulated. This dating method is used by geologists and paleoanthropologists in order to understand very great expanses of time and the deposits that the earth has formed. One paleoanthropological example of how the technique has been used is in bracketing the age of deposits at Olduvai Gorge where hominin remains have been found. The scientists have dated lava flows above and below the deposits where fossils have been found. Other paleoanthropological discoveries have also been dated using this technique. It is well suited to sites that show evidence of volcanic activity, as in the case of East African sites like Hadar, Ethiopia.