Take a long, narrow strip of paper. Tear it in half crossways. Tear one of the remaining pieces in half. Continue until you have made five tears. Measure the length of the piece you have remaining. Use this information and the number of times you

“halved” the paper to determine the length of the original strip of paper. This is analogous to the way in which the measurement of radioactive isotopes can be used to determine the age of rocks.