We have a radioactive isotope called RI which has a half-life of 9 million years. A geologist has used radiometric dating and determined the rock to be approximately 18 million years old. How many half lives have taken place? 1 2 3 4

Question

We have a radioactive isotope called RI which has a half-life of 9 million years. A geologist has used radiometric dating and determined the rock to be approximately 18 million years old. How many half lives have taken place?  1  2  3  4

anonymous · Answer

Is the answer 1, 2, 3, or 4? Can you explain it to me? I'm confused... Half lives were the hardest thing for me to learn in this module and I don't remember it well