We also need nitrogen, which is part of every protein and DNA molecule in our body. How do we obtain this element that is so essential for life? Although about 78 percent of the air around us is nitrogen, neither plants nor animals can absorb it directly. So nitrogen in the air must be converted into other forms before it can be taken in by plants and later utilized by humans and animals. How does that conversion, or fixation, occur? In various ways. One way is by the action of lightning.a Nitrogen fixation is also accomplished by bacteria that live in nodules on the roots of legumes, such as peas, soybeans, and alfalfa. These bacteria convert atmospheric nitrogen into substances that plants can use. In this way, when you eat green vegetables, you take in nitrogen, which your body needs in order to produce proteins. Amazingly, we find species of legumes in tropical rain forests, deserts, and even tundras. And if an area is burned over, legumes usually are the first plants to recolonize.

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“Each of the elements central to life—carbon, nitrogen, sulfur—is converted by bacteria from an inorganic, gaseous compound into a form that can be used by plants and animals.”—The New Encyclopædia Britannica.