Ted Nield, editor of Geoscientist magazine from 1999 to 2018 mulls over an ambitious opus on the sixth element, as he reviews Symphony in C: Carbon and the Evolution of (Almost) Everythingby Robert M. Hazen, published by W. W. Norton & Company (2019). As Robert Hazen tells us more than once in Symphony in C, most of Earth’s carbon is inside the planet. Nothing remarkable there — most of Earth is ‘inside the planet’, just as most of an orange is inside the orange. But Hazen, a mineralogist and astrobiologist, is right to emphasize this in his all-encompassing survey of the element in nature. The carbon cycle we usually learn about, first described by Enlightenment scientists Joseph Priestley, Antoine Lavoisier and Humphry Davy (although you won’t find that information here), seems to take place mostly on Earth’s surface.

Once we accept that the carbon cycle involves rocks as well as water, air and living things, we vastly extend its time dimension. Carbon-rich rocks, such as limestones, are sucked inside Earth at plate margins. Some of what goes down comes back up through volcanoes. But how much stays below, to be added to the carbon in the slowly churning mantle? And what about the carbon in the nickel–iron core?

Hazen is the executive director and motivating force behind the Deep Carbon Observatory (DCO), a ten-year global, multidisciplinary research project into all aspects of Earth’s carbon budget, which ends this year after long-term support from the Sloan Foundation in New York City. He admits that he had no idea how to write a book this comprehensive, until someone suggested that, as an experienced orchestral trumpet player, he should think of it as a symphony. Like composer Gustav Mahler, Hazen tries to ‘contain the world’, but he must squeeze it into a suitcase of dimensions more befitting the concision of Franz Joseph Haydn.

An ode to carbon