EARTH AND LIFE

A scientific exploration of how geology affects biology, and vice versa.

Knoll is a student of geobiology, “the study of how Earth and life interact and have done so through time,” a relatively new field that flowered with the work of James Lovelock, whose “Gaia hypothesis” envisioned our planet as a living system that, ideally at least, regulates itself through “interacting processes.” In that view, living beings are the fundamental drivers, living beings that are based on carbon—and, as Knoll notes, carbon isn’t especially abundant on our planet, which makes terrestrial life all the more fortuitous. In a memorable phrase, Knoll defines ecosystems as “complicated machines…[that] populate a slightly leaky cycle that moves carbon from the environment and back again.” That self-regulating system has its weak points; as Knoll notes, volcanic activity has threatened life with mass extinctions, and of course human technology is doing the same today. Knoll’s narrative begins in a more or less reader-friendly manner, but the science becomes more complex and the storyline a touch knottier as he proceeds (“scientists commonly assume that on geologic timescales microbial nitrogen fixation keeps N in ready supply, highlighting the importance of P as a limiting nutrient”). Essential to his discussion, however, is the thin skin of soil that veils the earth, with all their bacteria, archaea, nematodes, and burrowing critters that keep the whole carbon-moving cycle up and running. “If you want to discover evidence of life on another planet, look for genuine soils,” he counsels, and in that regard, among so many others, our Goldilocks planet is rare indeed, with plate tectonics, oxygen, and other uncommon ingredients combining to constitute what Knoll calls “the conversation between Earth and life,” one that requires us to clean up our act if it’s to continue.

Occasionally challenging, but a welcome look at the Earth as a single system of countless moving parts.