The half-life of a radioactive isotope is 10,000 years. This isotope and its breakdown product do not normally occur together before molten rock cools and becomes solid. You analyze a volcanic rock and find 25 percent of the original amount of

radioactive isotope remains, and 75 percent has decayed to its daughter element. How long ago did the rock solidify?

A) 2,500 years ago B) 20,000 years ago C) 50,000 years ago D) 10,000 years ago


Answer: B

Biology & Microbiology

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What happens when the resting potential reaches threshold voltage?

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What determines the direction of the voltage change that occurs at the postsynaptic membrane?

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