One way of understanding the environment is to understand the way matter and energy flow through the natural world. For example, it helps to know that a fundamental law of nature is that matter can be neither created nor destroyed. That law describes how humans can never really "throw something away." When wastes are discarded, they do not just disappear. They may change location or change into some other form, but they still exist and are likely to have some impact on the environment.

Perhaps the most important laws involving energy are the laws of thermodynamics. These laws were first discovered in the nineteenth century by scientists studying heat engines. Eventually, it became clear that the laws describing energy changes in these engines apply to all forms of energy.

The first law of thermodynamics says that energy can be changed from one form to...