A paleontologist estimates that when a particular rock formed, it contained 12 mg of the radioactive isotope

potassium-40, which has a half-life of 1.25 billion years. The rock now contains 3 mg of the isotope. About how old is the
rock?



a. 2.5 billion years
b. 5.0 billion years
c. 1.25 billion years
d. 0.3 billion years
e. 0.4 billion years


ANSWER: a

Biology & Microbiology

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