A space mission to the Moon collects rocks on the surface of the Moon, and deliv

Question

A space mission to the Moon collects rocks on the surface of the Moon, and delivers them back to your lab on Earth. Assume that all the argon-40 in a rock comes from radioactive decay of potassium-40.

a. One lunar rock you study has equal amounts of argon-40 and potassium-40. How old is the rock? Explain.

b. You examine another lunar rock, and conclude that it has three times as much argon-40 as postassium-40. How old is the rock? Explain.

c. Would you expect to find any lunar rocks with 100 times as much argon40 as potassium-40? Explain your reasoning.

*** I only need the answer to part c). Thanks!

Explanation / Answer

Part C: potassium decays into argon from 1:1 ratio to 1:2, 1:4, 1:8 etc. The amount of argon in each case will be 1:1, 1/2, 3/4, 7/8 etc. The ratio can never touch 100 as there will be a smaller portion if potassium decay for billions of years. As one half life itself is 1.3 billion years. Therefore accurate complete decasy of potassium that is 100 times argon is not possible.

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