Unraveling time and the Earth's biologic history are arguably geology's most important contributions to humanity. Yet it is very difficult for humans to appreciate time beyond that of one or two generations, much less hundreds, thousands, millions and billions of years. Perhaps we can only hope that students catch glimpses of our rich geologic heritage, particularly when most of our teaching is done in a classroom and not in a field setting. This exercise begins to make time more "three dimensional" and most importantly, students gain a better appreciation for geologic time and our Earth's history.

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The atmosphere is a mixture of gases. Similarly, the world's oceans and fresh waters contain dissolved chemicals. Many substances dispersed in air or water are measured in parts per million. Some of these substances are colorless, odorless, and tasteless, yet even in small quantities they can be toxic. To develop an understanding of parts per million as a concept, teams of students will create successive dilutions of a solution to reach a parts-per-million concentration.