This Mystery Science short video could be used to introduce the concepts of time scale in scientific learning. Scientists ask some hard questions that can take a long time to figure out an answer. Here the question posed is "How old is the earth?" The video tells of various ways that have been used to try and answer this particular question. After viewing the video kids will know the age of the earth but they will also understand that newer scientific techniques continue to help scientists uncover more information to help make more accurate answers to all the hard questions we use science to investigate.