Sometimes I like to just be still and think about my bones.

It’s something I regularly do when I’m bored and trying to make the hours melt away. The last time was while I was hiding from a torrential downpour in Utah’s eastern desert. To be fair, bones were already on my mind. I had spent days toiling away in the 105‐degree heat—nothing like fieldwork in July—on the petrified bed of a 157‐ million‐year‐old dinosaur, the skeletal pieces only stubbornly letting us take them from the rock. It was slow work, the passage of time tracked by the amount of stone chipped away from the maroon‐ colored bones and the gradual thunderhead buildup over the distant Abajo Mountains. Now and then, those storms would visit and give the crew an excuse to huddle in a shallow sandstone cave downhill from the elevated quarry, trying to forget the fact that lightning could still strike us there.

During these forced breaks, most of the crew would close their eyes and start to doze. Rhythmic snores lulled those who hadn’t al‐ ready drifted. But I couldn’t sleep. Relaxation has never come easily to me. Instead, my arms folded behind my head and the tips of my boots misted by the downpour at the edge of the overhang, I thought about my skeleton. If I were to be totally stripped of all my flesh and viscera, but still kept alive by some kind of magic, what would I look like as I lay there? An X‐ray version of myself, each joint shifting and flexing as I tried to get comfortable and as I simply breathed, my rib cage slightly expanding and falling back even as I tried to remain completely still. Would anyone be able to tell it was me? Maybe. Once, while at a conference in Washington, D.C., an osteologist acquaintance of mine walked up from behind and said, “I knew it was you from the shape of your skull!” It was an odd sensation to try to focus on my bones—not so much an out‐of‐body experience as an inner one, trying to envision each of the two‐hundred‐some‐odd parts in their place.

Try the meditation yourself sometime. The next time you’re waiting for a flight or for a movie to start, or if you can tear your eyes away from your smartphone in a moment of quiet, think about your bones. Concentrate on what’s beneath the surface, what you can sense but cannot see. Hands are wonderful for this. They’re the most mobile parts of our ape skeletons, after all, and among the most personal. Hands are how we experience so much of the world around us, and they carry more character than we often realize. And inside the rind of skin, muscle, and ligament are stacks of flat, fiddly little bones, connected to your lower arm by a gap that ends up making a flexible hinge. Then try it with the other parts. There’s a spine inside you. There are all those skull bones, biologically welded together just below the surface of your skin. Trying to envision what a navicular or cuneiform is doing at any one moment is probably going too far in, but you get the idea. Envision your skeleton by itself for a moment, the core of who you are.

But that’s only considering the skeleton as a fact of nature, a manifestation of what is . What all those bones mean depends on your point of view. When I think of bones, I think of Darwin’s “endless forms most beautiful and most wonderful.” Everything about the bones inside us, from their arrangement to their microscopic structure, is a testament to the way evolution mixes blind chance with the winnowing edge of natural selection. By mixing and matching old parts, forced along only by what’s useful in any given moment, what’s old becomes something new. But that’s hardly all. We carry the past in our bones. Our species is relatively young, still a long way away from the million‐year average that most mammals tend to persist, but even though we prefer to believe in our novelty, our skeletons underscore the truth. The basics of our body plans were forged in the seas in a series of happenstances, with tweaks and refinements coming from life on land and in the trees. Our evolution continues, but we’re mostly able to pick out these differences because we’ve developed a talent for noticing patterns in our own species. From the broader view of the fossil record, there is nothing about you or me that is particularly unexpected or staggering. We’re variations on a theme, a new combination of features that makes us stand out but also, more important, joins us to a history longer than any of us have a hope of truly and fully comprehending.

I can only imagine what a future intelligence—our descendants? life from elsewhere? another species that happens to evolve the wisdom to examine its past?—would make of us, or at least those of us who leave our bones to the fossil record. It’s really the best chance we have at lasting beyond ourselves. The legacies that we try to build are either dimmed or destroyed by the passing of time. There is almost nothing that we can create that holds any permanence. But if summer after summer of scuffing my boots on arid rocks and feeling the back of my neck crisp as I scan the ground has taught me anything, it’s that bones are the one chance we have at lasting millions upon millions of years, the purest and most minimalistic records of who we were. Even better, we don’t have to wait for happenstance. With a little forethought, and hopefully someone willing to carry out our wishes, we can become fossils.

The thought first occurred to me while hiking alone down Park Avenue of Utah’s Arches National Park one June afternoon. There were no towering skyscrapers here, but from the tall stone walls, it was easy to see how the short trail got its name. And even though it was not remote by any means—you can stand at one end and see the park traffic go by at the other—the orange and rust sandstone provided that most essential of desert comforts, shade. It was peak season, but I hardly saw another person as I ambled along the slickrock below, a few croaking ravens perched in the nooks of the Jurassic rock above being my main company. And after I turned around and started to make my way back, I stopped to look at the sandal prints I’d left behind in a few dry pools of rust‐colored sand. How long would they remain there? Would they have any chance of withstanding the ages, like the dinosaur tracks that pock the stone at various places around the park? Not likely. If they weren’t brushed over by another tourist, the wind or occasional thundershower would wipe them away, not to mention that this desert was an erosional environment—a place where the elements were chipping rock away and moving it elsewhere, not laying it down to be preserved in perpetuity. But the petrified cogs of my mind kept whirring as I climbed the trail back to the road. In slightly different circumstances, those prints might have been preserved for a time as deep as the surrounding rock walls. The fossil record isn’t something of the past, but grows every single day existence keeps rolling on. If I were to become a fossil, how would I want to do it?

Fossil is not synonymous with bone. Footprints can be fossils. In fact they’re sometimes more informative about the way an animal lived than bones are, given that traces are actual moments preserved in stone, like the trail at Laetoli. I could pick various mudflats and lakeshores, walking back and forth barefoot to leave my tracks behind, and if I’m lucky, some of those might dry up and harden only to be buried and preserved by the next wave of incoming sediment. (Or if I really wanted to confuse paleontologists of the future, I could leave my sandals on, letting them wonder what “Vibram” means.) But the thought of tracks being my permanent record doesn’t appeal to me very much. All the future would know of me would be the soles of my feet and, with the right calculations, my height, walking speed, and the fact that my feet tend to turn outward as I go along. Nor was I very happy with the contributions to the fossil record I’ve already made. Like billions of others, I have generated plenty of garbage that’s rotting in trash heaps and driven vehicles that have belched a horrific amount of greenhouse gases into the air, contributing to the biological crisis that may mark this time in history not so much as an era but as a mass extinction event. I don’t want my legacy to be a break of barren rock that marks the latest of the worst die‐offs in history. Bone has to be the way to go, and here a science called taphonomy will be our guide.

Even though it didn’t have a name yet, taphonomy got its start with the help of the eccentric British clergyman William Buckland. Buckland was off the mark with his identification of the “ Red Lady ,” but his main claim to fame was that he founded the study of how fossils are made. This was his work at Kirkdale Cave in Yorkshire.

In 1821, local quarry workers found a cavern with a vast jumble of bones buried in its floor. Laborers, amateur collectors, and local parish heads all descended on the spot, plucking up mementos from this place that was said to be paved with osteological treasures. Early identifications suggested a mix of animals—mammoths and rhinos as well as foxes and abundant hyena bones—and this news puzzled Buckland. Deposits like this were supposed to come in one of two flavors. There were fissures that the bones of long‐lost herbivores were swept into—a phenomenon Buckland attributed to the “Noachian deluge”—or caves that carnivorous mammals used as dens. To have an abundance of both kinds of remains didn’t seem to make any sense. So, despite the winter chill, Buckland crawled into the cave himself, and even though collectors had already been messing around in the cramped space, he nevertheless was able to determine that there was no fissure for animals to tumble in through. They must have been dragged in here by the voracious hyenas at a time that, from the cave’s geology and a Christian faith that did not yet have to reconcile with the reality of millions of years of evolutionary change, Buckland put at just before the great flood.

But it’s one thing to come up with a story and another to test it. That’s what science requires—the persistent but essential little gremlin that whispers, “Is this testable?” when you think you’ve come up with a brilliant solution to a problem. Buckland did just that. Among the fossils previous collectors had overlooked was something that Buckland had already taken a keen interest in—prehistoric poop. He plucked up a few of these plops, suspecting that they had been left by the cave’s hyenas, and, sure enough, his chemist friend, William Wollaston, confirmed that the scats had exactly the high bone content you’d expect. Buckland even went so far as to ask France’s Georges Cuvier, the most respected anatomist of his or perhaps any era, to send him the crap of a hyena that lived at the Museum of Paris, and these comparisons, as historian Martin Rudwick wrote, “clinched the case.”

But Buckland did something else that was just as critical. After he returned to Oxford, the implications of the cave for connecting the past world to the present buzzing in his skull, a traveling show with a spotted hyena passed through town. Buckland offered the beast a selection of ox bones and watched carefully which ones the hyena plucked up, how it broke them open, and, eventually, what came out the other end. It turned out to be a near‐perfect replay of what must have happened at Kirkdale; the pattern of breakage and gnawing was practically identical to the fossil bones from the cave. Modern hyenas had bridged the gap between the world as we know it and what came before, even explaining their part in forming the fossil record by bringing bones into a place where they would eventually be covered.

You can still see some of those experimental bones today in a quiet little corner of the churchlike Oxford University Museum of Natural History. These cracked remains are behind a glass pane with a few fossilized and more recently gnawed bones side by side. They’re beautiful, despite the bone‐crushing violence that created them, and I wanted to run around to the quiet families gazing at the hall’s dinosaur skeletons and drag them over to the darkened corner to show them the bones that launched a science. I held back from doing so—everyone knows that unless you’re a paleontologist or archaeologist yourself, a strange man insisting that you look at old bones is how horror movies start—but, really, I just wanted someone to share my joy as I fawned over the battered fragments propped up behind the glass. They weren’t just hyena leftovers, but proof of the geological maxim Buckland’s student Charles Lyell would eventually coin—“The present is the key to the past.”

The reaction to Buckland’s “hyena story” was momentous. Even if his colleagues looked down their noses at his methods—what distinguished professor wrote letters to acquire fresh poop?—they could not argue with his results, particularly as he attempted to place Kirkdale Cave in the context of how the world had changed. Buckland even won the highest honor available to geologists, the Copley Medal, for this work. That’s why it’s strange that his interest in reconstructing prehistoric events did not catch on among his peers. Maybe it was too dirty for the respectable men of science. Perhaps fieldwork, crawling through caves and feeding carnivores the butcher’s leftovers, did not appeal to anatomists, who preferred the cleanliness and order of the museum lab and writing desk. Or maybe it was because there was so much novelty in the fossil record that simply describing the various pieces that had been found and how they fit together was a job bigger than any scientist could hope to accomplish in their lifetime. Especially when the badlands of the American West were found to spill out an abundance greater than anything ever seen in Europe.

Still, the bigger point of any study of prehistory is to put the past in its place against the watermark of the present, perhaps even joining the two. As much as I love the phrase “lost worlds,” the fact is that it has always been the same world, with today’s life inextricably entwined with that of the past. Processes that occur now did not just pop into existence for us to observe them—they’ve been going on as long as there has been life.

Adapted from SKELETON KEYS by Brian Switek, published by Riverhead, an imprint of Penguin Publishing Group, a division of Penguin Random House LLC. Copyright © 2019 by Brian Switek.