The radioactive form of K K40 has a half life of 125 billion

The radioactive form of K (K40) has a half life of 1.25 billion years and decays to Ar0 A microfossil was found in a rock with 25% K40 and 75% Ar40. How old is the microfossil 1 year old B. 1.25 billion years C. 2.5 billion years D. 5 billion years Copyright The McGraw-Hill Companies Inc Permission required tormproduction or display Radioactive decay Amountof daughter isotope .50 Amount of parent isotope Time in halt-lives

Solution

Answer:

The term half-life is the time it takes for one-half of the atoms of a radioactive material to disintegrate.

Let\'s assume a rock is 100% K¹⁰, it takes 1.25 billion years to become 50% K¹⁰

Now we have 50% K¹⁰ It takes another 1.25 billion years to become 25%.

In total = 1.25+1.25 =2.5 billion years