Asked by cindy

The isotope potassium-40 (40K) decays into the isotope argon-40 (40Ar) with a half-life of 1.25 billion years. Suppose we find a rock in which seven-eighths of the potassium-40 has decayed to become argon-40, and only one-eighth of the original potassium-40 remains.
Answered by Steve
1/8 = (1/2)^3
so, 3 half-lives have passed.
Answered by ridge
2.6 billion years
Answered by jeff
69 hahahahaha
Answered by wyatt d'spain
69.420 billion years lol ()
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