Mystery Science offers this video that answers the question, ‘How old is the earth?’ by examining the different natural events that function as indicators of time. The host, Doug, takes participants on a journey looking at natural markers such as tree rings and sediment layers within rocks to determine the age of planet Earth. He presents the information in an engaging fashion using age-appropriate vocabulary and explanations while celebrating the work of scientists whose efforts around radioactivity has brought them to an answer to this question.