Iron, Nature's Universal Element: Why People Need Iron & Animals Make Magnets

Earth's living systems use nearly every element, but iron plays a particularly important role, and it is not clear that it could be replaced by other elements. Eugenie Mielczarek, a physicist, and Sharon McGrayne, a science writer, describe in their very readable Iron, Nature's Universal Element the importance of iron for life. The book is entertaining, amusing, and challenging and, despite the elementary level, contains some new information for most readers.

One could expect that a popular book, covering topics from the origin of life to bird migration and the ecosystem, would contain some mistakes. I did not find any; besides being very careful, the authors had the book reviewed for scientific accuracy by many of their friends. A brief description of some of the topics covered and some quotes will give an idea of the wide range covered and of the style of the authors.

In the first chapter, the authors describe the emergence of life, nearly four billion years ago. Life began without oxygen, and relics of this early time most likely survive deep in the oceans, in complete darkness and under immense pressure. The actual origin of life is not known with certainty, but the authors provide a balanced brief review of a conceivable beginning, in which iron is part of the necessary energy source. They describe the ocean floor as a giant laboratory, where one-cell organisms cluster around hot vents and form the food for larger organisms: "Tube worms at the sea vents farm archaea, much like rangers raising cattle."

The second chapter begins with the sentence "Life on earth has at times been devastated by great ice ages, flip-flopping climates, volcanic eruptions, asteroidal collisions, massive extinctions, and other natural disasters, but the most catastrophic of these was the appearance of oxygen molecules in the atmosphere beginning a little less than 2 billion years ago." The book goes on to explain how living things overcame the problem: either by escaping into the anoxic depths of the oceans or adapting to and using the oxygen. Iron was (and is) essential for making the second alternative possible.

The ways living systems learned to deal with oxygen, and how iron is used, are described simply and correctly. Again, stories enliven the scientific accounts. For instance, one story tells about the men of the Bantu tribes whose livers "rusted" because they drank too much homemade beer brewed in iron pots. This story makes the point that iron is both necessary and toxic.

Iron is essential in many proteins, hemoglobin being one example. The book describes the basic aspects of the use of iron in enzymes, but the authors also include other biological uses for iron. For instance, iron is incorporated into tiny magnets, which some anaerobic bacteria use to avoid oxygen and which some birds and sea turtles use for directing their travels.

The authors describe the involvement of iron in two of the most fundamental life processes: photosynthesis and nitrogen fixation. Both of these processes are essential for our ecosystem, to which the book devotes considerable attention. Finally, the last chapter, "Feeding the World's Poor," describes the tragic consequences of dietary iron deficiency in large parts of the world.

A clear glossary and an extensive and excellent bibliography complete the slim book and permit the reader to dig deeper. In summary, I can recommend the book without reservation. In particular, physicists who have not delved into the life sciences may find it stimulating.