Life Sculpted Tales of the Animals, Plants, and Fungi That Drill, Break, and Scrape to Shape the Earth

Though we marvel at the creative side of evolution, the destructive flip side of that coin often gets less attention. Since its first stirrings, life has been involved in a war of attrition with its environment, "breaking, scraping, drilling, or otherwise changing the solid to the not-so-solid" (p. x). Leave it to palaeontologist Anthony J. Martin to write a witty book that boils over with fascinating studies about one of the more obscure corners of biology: bioerosion.

Martin's speciality is ichnology: the study of animal traces, both modern and fossilised. I have reviewed and enjoyed his two previous popular science books on this topic, Dinosaurs Without Bones and The Evolution Underground. Life Sculpted focuses on a subtopic within ichnology: bioerosion, the process of life eroding hard substances in its environment, and the traces this leaves behind. How about I break this down?

Life Sculpted is divided into chapters dealing with the erosion of rock, shell, wood, and bone. Rock is attacked by a wide array of organisms and Martin describes how cyanobacteria, fungi, lichens, chitons, sponges, worms, barnacles, clams, and a host of other species attack rock by scraping, drilling, gouging, and dropping acid. Martin poetically describes it as "a wholesale slaughter of landscape exteriors that reveals illusions of immutability" (p. 25). In the process, they leave behind species-specific patterns of grooves, pits, scratches, and other traces. Martin points out that the cumulative effect is so large that the rock cycle has become as much geology as biology. Vertebrates get in on the action too, as evidenced by what is the most glorious chapter title in this book: "Your Beach Is Made of Parrotfish Poop". Because, yes, that beautiful white sand found on tropical beaches? That comes out of the behind of parrotfish crunching corals in the process of scraping algae off them. The biological details of this ecosystem—which fish do it and why coral reefs are not harmed by it—are fascinating.

But life equally excels at attacking the living environment. Almost as soon as shells evolved, other invertebrates evolved ways of drilling into them, with trace fossil evidence dating back at least 500 million years. And if not death by drilling, shelled creatures have faced death by crushing from crustaceans, marine reptiles, mantis shrimp, seabirds, and mammals such as otters. Wood similarly was under attack almost as soon as it evolved by insects, later to be joined by (expectedly) woodpeckers and (unexpectedly) dinosaurs munching on rotten wood, possibly for the extra nutrition afforded by its fungi and insects. Wood furthermore has a second life as driftwood, which allows Martin to introduce one of the most amazing fossils: a large log covered by crinoids. Though they superficially resemble flowers, crinoids are actually echinoderms that spend a large part of their lifecycle attached to substrates. Martin tells the fascinating story of how these crinoid colonies were a temporary phase in life's history, eliminated by the evolution of wood-boring clams that from then on prematurely sundered these rafts.

Finally, the erosion of bone is an opportunity to dedicate a whole chapter to the wonderfully weird world of whale falls and the worms that feed on them. When whale carcasses sink to the bottom of the ocean, they become a miniature ecosystem that lasts for decades, broken down by an ever-shifting cast of scavengers including worms of the genus Osedax that drill into their bones and settle there. Lovingly nicknamed snot or zombie worms, they were only described in 2004. On land, meanwhile, bones are munched on by a diverse cast of organisms looking to supplement their diet with calcium, including surprise appearances by squirrels and assorted herbivorous mammals. Martin goes a bit off-piste here I feel, drifting into a discussion of life's most powerful biters.

The biggest bioeroders of them all in terms of volume are probably humans. What started fairly innocently with our ancestors using stone and bone tools has turned into a planet-altering industry. In the process of extracting the resources to make our material world, we drill, scrape, dig, bore, and tunnel like nobody else. The problem is that this is such a massive topic—encompassing basically all of archaeology and economic geology—that it could be a separate book. Martin here merely gestures at it in the final brief chapter, which is not quite a satisfying ending to this book.

Part of the fun in reading Life Sculpted comes from Martin's humour, though I get the feeling he has toned it down a bit compared to his previous two books. Even so, expect a healthy dose of wit (the boundaries of primitive tectonic plates "supplied both a kitchen and a recipe for primordial soup" (p. 26)), alliterations (mussel muscle), puns (a history of boring boring? Get out!), and the occasional deep cut (how do you calculate the bite force of T. rex when there are no lawyers around?).

One topic I felt Martin could have emphasized more is the importance of a search image for something. There are behaviours for which we do not yet have trace fossil evidence because we do not know what to look for. This was made explicit in Dinosaurs Without Bones but only hovers in the background here. One example is that we have no trace fossils of lichens because we do not know how to distinguish them from fungi trace fossils or chemical and physical weathering. Similarly, woodpeckers have made holes in trees for over 20 million years, and yet we have not been able to identify pecking traces or nest holes in the fossil record that can be reliably attributed to these birds. Another theme that is mentioned in places but not developed further is how climate change will affect bioerosion in the future. Perhaps that would have made a fitting chapter to end the book with.

By all accounts, this is a book I should utterly adore and I was engaged throughout. Still, I admit I felt ever so slightly underwhelmed after finishing it, though I struggle to put my finger on the why. Perhaps the best way I can explain it is that I feel it lacks a throughline or overarching theme that takes it beyond just a list of the wondrous and bizarre. And I write this while acknowledging that it is exactly the wondrous and the bizarre that propelled me through the book.

Life Sculpted brings together a bewildering array of weird and wonderful creatures and studies from the borderlands between palaeontology and evolutionary biology. Ichnology is already an obscure discipline that few people will have heard of, and bioerosion is a subject that will be on the radar of even fewer people. Leave it to Martin to turn that into an arresting book that is both a smooth and fun read.