Lessons Trapped IN Stone
by Kenneth Lacovara
A fellow of The Explorers Club since 2003, paleontologist Kenneth Lacovara, PhD, has excavated some of the world’s largest dinosaurs, including the behemoth Dreadnoughtus, which at 65 tons, outweighed nine T. rex. Lacovara is the Founding Dean of the School of Earth & Environment at Rowan University, and is Founding Director of the Jean and Ric Edelman Fossil Park, where he and his team are unraveling the mysteries of the extinction of the dinosaurs. His book, Why Dinosaurs Matter (Simon & Schuster, 2017), is winner of a Nautilus Book Award, and his 2016 TED Talk was rated one of the year’s top three. Lacovara is the recipient of this year’s 2019 Explorers Club Medal, the Explorers Club’s highest honor.
You got lucky. And so did I. That’s the resounding, persistent message of the Earth’s rock record. Our planet’s history is a chain of happenstance, four and a half billion years long. Most events along the chain are miniscule and commonplace—the products of slow acting, everyday processes. The imperceptible tunneling of a tree root that cleaves a rock in two. The delicate buzz roll of raindrops that return a mountaintop to the brine. The lofty trade winds that buoy silt along an intercontinental voyage. The rhythmic swash and backwash that arbitrates the joining of the land and the sea.
Over the brief glimmer of a human lifespan, these tiny natural acts do their work in ways that are largely insensible to us. Though weak, they should not be mistaken for impotent. They are endowed by the great engine of geology—deep time—with the power to raise up landscapes and to cut them down again. These feeble exertions have built the mountains, carved the canyons, filled the bottomlands, and sculpted the coastlines. For the most part, they do the work of shaping our world. But the humdrum of everyday geological processes is punctuated, rarely, but importantly, by the occasional catastrophe.
Our world has had oxygen crises and carbon dioxide crises. It has iced over from pole to pole at least twice. Asteroids and comets have pummeled it. Seas have sloshed on and off the continents. Ocean chemistry has gone bad. And our magnetic field, our great shield against the solar winds, has often failed us. Alone or in combination, these calamities have wiped out more than 75 percent of species on at least five occasions. The geosphere is resilient, tough, and the landscape is quick to slough off these transitory insults. The biosphere, on the other hand, is thin, precariously balanced, and easy to damage. Whereas geological history can repeat itself, evolutionary history is a one-way street. Once set upon a new path, the course of biology is forever altered.
Three decades of digging into Earth’s past have taught me that all of it matters, the unremarkable processes and the extraordinary catastrophes. Together they form a singular thread of events whose culmination is the fleeting series of instances that we perceive as our present, a reality that is thoroughly contingent upon innumerable past occurrences. The rocks will whisper “It didn’t have to be this way” to anyone willing to learn their language. In my 2017 book, Why Dinosaurs Matter, I address the improbability and the wonder of our particular path through history:
The latest page of this epic—the one we call the present—has an air of inevitability, but it is the product of innumerable contingencies that lined up in just the right way to create the world that we know. It could have been otherwise. Disturb something here, delay an event there, reorder a single step in a long sequence, or shift a continent this way or that, and Earth history changes forevermore. A single sunbeam, causing a single mutation, is all that it takes. A space rock nudged an infinitesimal degree to the left or right could change the course of all it is yet to pass. Kill off a mundane wolflike creature on the ancient shores of Pakistan, and today there are no whales. Shift the winds one way or another across northern Africa six million years ago, and humans evolve or do not evolve, as forests turn to grasslands, or not. The contingencies are endless and mind-boggling, an infinite kaleidoscope of things and events interacting with one another in ways that we may never fully understand.
Along the path from our wormy Cambrian ancestors to primates dressed in suits, innumerable forks in the road brought us to this very particular reality. But would it happen this way again? It’s nearly impossible.
If you made a thousand more Earths, in a thousand more solar systems, and let them run, you would always get a different result. No doubt, those worlds would be both amazing and amazingly improbable, but they would not be our world and they would not have our history. There are an infinite number of histories that we could have had, but we only get one. And, from a human perspective, we got an especially good one—the one that led to us.
When I am in the field, prospecting for fossils, these sorts of thoughts are never far from my mind. While life might be inevitable on planets that bear the right conditions, the chance of any particular species evolving into existence is vanishingly small. And within a species, the chance occurrence of a particular individual, such as you or me, is vastly more diminished. For those of us who discover fossils, we usually refer to them by their genus and species. For example, “I found a Tyrannosaurus rex femur,” or “I discovered a Hadrosaurus foulkii skeleton.” But really, we are finding individuals—individual members of their species whose existence was similarly improbable to yours.
In 2005, when I discovered a large sauropod dinosaur, whose genus and species I would later name Dreadnoughtus schrani, I happened upon the huge femur of a particular individual that roamed the (then) forested hills of southern Patagonia 77 million years ago. This titanic plant-eater was 26 meters long, stood two-and-a-half stories at the shoulder, and all fleshed out in life would have weighed 65 tons. That’s the mass of nine T. rex. We labored during five austral summers to extract 145 of its bones from sandstone and mudstone as hard as concrete. It lived—like you—an improbable existence. And, as with all individuals, it possessed a life history that was unique among its kind.
Most animals that perish on the landscape vanish quickly as scavengers tear their flesh and chomp their bones, and as the elements weather their corpses to dust. To enter the fossil record, an organism must make a rapid transition from the biosphere to the geosphere to forestall these recycling agents. This requires the coincidental death of an organism in just the right geological situation, one capable of burying the body rapidly.
How many Dreadnoughtus lived and died without contributing to the fossil record, I cannot say. Millions, probably. This particular giant, however, perished in a river that was bursting its banks and disgorging large volumes of water and sediment and whatever else was caught up in its flow onto its flood plain. There, this Dreadnoughtus quickly sank into a soupy mire that deprived the hungry scavengers of its body and the pitiless rain and wind of breaking it down. This serendipitous demise led to an exquisitely preserved fossilized skeleton of extraordinary completeness—the stuff of paleontological dreams.
Across the Tethys Sea, huddling in their Laurasian hidey holes, our ancestors were half a world away. They would not have known of the storm that toppled the banks of the ancient Patagonian river that caught Dreadnoughtus in its flow, but they did cohabit the same world. By this time, most of the genes that make up our human DNA had already come into being, stowed away in each warm cell of our tiny shrewy ancestors. As our fuzzy forebears padded vigilantly through steamy Cretaceous nights, they carried their fate and ours on their delicate frames as they crept timidly across the dinosaur world. The hegemony of the saurians would have probably persisted until the present were it not for a table-turning cosmic accident.
Following the fall of the non-avian dinosaurs 66 million years ago, our mammalian ancestors and their kin climbed out from the devastation and began an evolutionary extravaganza that filled many of the vacated dinosaurian niches and created still more de novo. Plesiadapiforms, precursors of primates, appeared almost immediately after the era-ending calamity. Then, by 55 million years ago, the true primates had appeared. The branching that set us hominins apart from our chimpanzee cousins occurred just six million years ago. Our own species, Homo sapiens, appeared 300,000 years ago, spurred on perhaps by a chaotic shift in climate.
And then there’s you and me—each of us with our own unique tale. My DNA results from National Geographic’s Genographic Project suggest that members of my paternal lineage departed Africa 70,000 years ago, followed 55,000 years ago by members of my maternal lineage. Dispersing through the Levant and the Caucasus, my ancestors of African descent reached Western Europe by about 35,000 years ago. However, some of my forebears were already there to meet them. DNA results from 23andMe indicate that I bear 343 Neanderthal variants of human genes. That means I have more Neanderthal variants than 99 percent of those tested—a heritage that I embrace and relish. Fast forward through most of Western civilization to the seventeenth century when some of my British ancestors sailed for the New World. Two centuries later, my Italian ancestors would follow. My immediate progenitors on both sides were born and bred in the Mid-Atlantic States. In 1947, my parents were wed, after an improbable blind date a year and a half earlier. Robert Lacovara and Ruth Marple had three boys and seven years later, hoping for a daughter, they had a fourth boy—me.
My story is by no means unique in its complexities and myriad contingencies. Yours is similarly intricate, and manifestly unlikely. Yet, here we are. If highly unlikely mishaps are known as “freak accidents,” it’s fair to say that we are all freaks of nature. It is this way for all species, and exponentially more so for every individual therein. Which brings me back to Dreadnoughtus.
The individual that I encountered in the rugged badlands of Patagonia lay underground for 77 million years. All the while, my lineage was evolving from shrews to primates to apes to humans.
It’s a common misconception that paleontologists dig for dinosaurs. We don’t, not for large ones. We dig once we’ve found them. And we find them by getting ourselves in the right geological situation and walking until we see bones sticking out of the rock. It’s not pickaxes and shovels that first uncover them, it’s erosion. As the land surface retreats under the unrelenting forces of wind, rain, frost, and a host of other physical and chemical processes, treasures from the past are exposed at the surface. Although a skeleton may persist for tens or even hundreds of millions of years underground, once exposed it will quickly weather away. After being uncovered, I’ve seen pristine fossil bone degrade to a crumbly mess in just a few days. Under the right conditions, bones may survive at the surface for a decade, or even a hundred years, but not much more.
Pulling it all together, the story goes like this: The species, Dreadnoughtus schrani, appeared in the Late Cretaceous Period after descending from a long line of ancestors that extend back to a bacterium that was the last common ancestor of all life on Earth. Most Dreadnoughtus left no trace, but one in particular had the poor fortune to perish in a mire that quickly entombed its body. The shrews that inhabited the far side of the planet would continue on well beyond this moment, secreting themselves in the shadows of the dinosaur world until the tables were turned by a chance encounter with an asteroid.
In the course of 66 million years, they would evolve into sentient beings that invented all manner of things never before seen on Earth, including science. By this time, the hillside above Dreadnoughtus had been pushed back dangerously close to its remains. A slight increase in the rate of erosion would have destroyed its skeleton before humans reached South America, before the Age of Enlightenment, and before we recognized dinosaurs as a thing. Had I reached this site a few years before, nothing would have been exposed and I would have trod unknowingly across the grave of this giant. Had I arrived a few years hence, its remains would have been reduced to unrecognizable bone fragments littering the bed of the nearby arroyo.
Given all these uncertainties and low probabilities, how can we find fossils? And how is it that paleontologists can encounter them with sufficient frequency to base their careers upon their discovery? Time. Deep time. Time in expanses well beyond any human comprehension. In a 2016 TED talk, I summarized it this way:
With seven billion peripatetic Homo sapiens on the planet, it was perhaps inevitable that one of them would eventually trod on the grave of the magnificent titan buried beneath the badlands of Southern Patagonia. I was that ape. Standing there, it was not lost on me that the chance of any one individual entering the fossil record is vanishingly small. But the Earth is very, very old. And over vast tracts of time, the improbable becomes the probable. That’s the magic of the geological record. Thus, multitudinous creatures living and dying on an old planet leave behind immense numbers of fossils, each one a small miracle, but collectively, inevitable.
We live in an amazing age on a stunning planet with a wondrous past, one that includes dinosaurs and the tiny fuzzballs that turned into us. We’re all freaks of nature and cosmic lottery winners, a revelation based on the rocks beneath our feet that inspires my immense gratitude and a feeling of connectedness with the events that led to this singular moment in time. It didn’t have to be this way. But it is. You got lucky. And so did I.