aoss 102 In a particular igneous rock sample, you find 12 nanograms of 40 Ar and

Question

aoss 102

In a particular igneous rock sample, you find 12 nanograms of 40Ar and 4 nanograms of 40K. What does this say about when this rock sample solidified?

A. It solidified sometime after oxygen was present in the atmosphere. B. It solidified sometime during the period when all the oxygen produced by microbes in the ocean was consumed in producing iron deposits. C. It solidified sometime after the Earth formed, but before life existed on Earth. D. It solidified before the the solar system formed.

Explanation / Answer

Since, the half life of potassium is 1.248×109 years, dating of the isotope give the results after the earth is formed. Here, decay was taken place 3 times. Hence, the it should be after the earth formation but before the life existence.

Hence, the correc option is C.

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