If an isotope has a half-life of 4 billion years, then in 4 billion years what will happen?

Question

Quizplus · Accepted Answer

Half-life is the time taken for half of a radioactive substance to decay. Therefore, after one half-life, half of the substance will have decayed and half will remain. After two half-lives, half of the remaining substance will have decayed (i.e. 1/2 x 1/2 = 1/4) and 1/4 will remain, and so on. Therefore, after 4 billion years (assuming the environment has remained constant), the original amount of the isotope will have undergone 1 billion years of decay, which equals 1/2 x 1/2 x 1/2 x 1/2 = 1/16 of the original amount remaining. So, half of the original amount will still be present.

If an Isotope Has a Half-Life of 4 Billion Years