Although organic chemistry is often described as the science of carbon, Robert Hazen’s latest book, Symphony in C, makes clear that this vital element cannot be contained by such a disciplinary boundary.
Despite its abundance and importance, the location and cycling of carbon on Earth are not yet well understood. Ever-increasing atmospheric concentrations of its dioxide form lend urgency to a more accurate accounting of this element. However, it is Hazen’s enthusiasm, the string of shareable facts presented, and the introduction of so many interesting scientists that make this book such a fascinating read. Trained as a geologist, Hazen also has a deep love of music, which manifests in the symphonic form that superficially organizes the book’s content into four alchemical movements: earth, air, fire, and water. In the first section, “Earth”—the most well-developed of the book—Hazen discusses carbon-based minerals, offering a wonderful account of how mineralogy has gradually turned from a purely observational science to one that can predict missing carbon-containing minerals. Hazen brings a distinct and intentionally personal perspective to this topic as head of the Deep Carbon Observatory (DCO), which brings together hundreds of scientists around the world to understand how carbon moves in all its forms in and around our planet. In 2015, the DCO started the “Carbon Mineral Challenge” to find the almost 150 carbon-containing minerals predicted to exist on or near Earth’s surface. Some of these predicted minerals, including a sodium lead carbonate called abellaite and green middlebackite, have already been found. The extreme pressures and temperatures hundreds of miles below Earth’s surface form denser crystalline minerals, but almost none of the ~400 currently known carbon minerals are in high-pressure phases. Hazen has been fascinated by experimental efforts to mimic these extreme pressures since he was a graduate student, and he details the methods being used to reach 80,000-fold or greater atmospheres of pressure. Such high pressures do not lead only to simple structures, we learn. Additional surprises await when Hazen explores deeper toward Earth’s core. The second section, “Air,” starts with a very brief history of Earth before discussing carbon in the air—primarily carbon dioxide—and its cycling through the atmosphere. Hazen finishes this section with a wonderful discussion of the biases that humans, including scientists, have and the challenges they bring to forming a more integrated picture of the world. “Carbon science is like that—a blending of concepts and principles from every branch of research,” he writes. “So, perhaps when we seek to understand the limits to knowledge—the nature of the unknowable—our own human limitations need to be placed at the top of the list.” “Fire” is devoted to the many ways we manipulate carbon, using it to create plastic materials, for example, as well as other products of modern organic chemistry. Here, Hazen presents an almost random assortment of historical anecdotes about carbon-based materials, from methane to neoprene to paper, giving the reader a sense of the diverse forms carbon can take. This section is the shortest, and readers hoping for more detail might turn instead to Mark Miodownik’s recent book, Liquid Rules (reviewed in Science on 8 February 2019). The final movement is the most speculative as Hazen describes the many scenarios that may account for the origins of carbon-based life forms. He makes clear his own biases—he believes that mineral surfaces were crucial to the formation of the small organic building blocks of life, for example—as he gallops through a history of this field. The final pages of the book end with a very personal look at what Hazen calls the “human carbon cycle”—exploring how we consume and expel carbon—and examines our responsibility to our carbon-based home. “If we are wise, if we can temper our wants with a renewed sense of awe and wonder, if we can learn to cherish our rhapsodically beautiful carbon-rich world as it so urgently deserves, then we may hope to leave an unrivaled, priceless legacy for our children, their children, and all the generations to come.” Given the incredibly wide range of the earlier chapters, this philosophical ending fits. Throughout Symphony in C, science is presented as a living and very human endeavor. Hazen fills the book with scientists and collaborators from around the world and with his own research stories. An eight-page insert of photos, which depict not only mineral structures and timelines of the Earth’s evolution but also the men and women working to extend our knowledge, reinforces the human part of the grand story of carbon. The rapid pace of research in the areas presented could quickly warrant another overview, but for now, this very readable account should inspire a much broader interest in carbon. About the author The reviewer is at the Department of Chemistry, Indiana University, Bloomington, IN 47405, USA.