Humans now live in a new geological epoch of our own making: the Anthropocene. Or so we’re told.
by Peter Brannen edited by O Society August 21, 2019
Whereas some epochs in Earth history stretch more than 40 million years, this new chapter started maybe 400 years ago, when carbon dioxide dipped by a few parts per million in the atmosphere. Or perhaps, as a panel of scientists voted earlier this year, the epoch started as recently as 75 years ago, when atomic weapons began to dust the planet with an evanescence of strange radioisotopes.
These are unusual claims about geology, a field that typically deals with mile-thick packages of rock stacked up over tens of millions of years, wherein entire mountain ranges are born and weather away to nothing within a single unit of time, in which extremely precise rock dates—single-frame snapshots from deep time—can come with 50,000-year error bars, a span almost 10 times as long as all of recorded human history. If having an epoch shorter than an error bar seems strange, well, so is the Anthropocene.
The idea of the Anthropocene is an interesting thought experiment. For those invested in the stratigraphic arcana of this infinitesimal moment in time, it serves as a useful catalog of our junk. But it can also serve to inflate humanity’s legacy on an ever-churning planet that will quickly destroy—or conceal forever—even our most awesome creations.
What paltry smudge of artifacts we do leave behind, in those rare corners of the continents where sediment accumulates and is quickly buried—safe from erosion’s continuous defacing—will be extremely unlikely to be exposed at the surface, at any given time, at any given place, tens of millions or hundreds of millions of years in the geological future. Sic transit gloria mundi.
If they then somehow found an accompanying plaque left behind by humanity that purports to assign this unusual layer its own epoch—sandwiched in these cliffs, and embarrassed above and below by gigantic edifices of limestone, siltstone, and shale—this claim would amount to evidence of little more than our own species’ astounding anthropocentrism. Unless we fast learn how to endure on this planet, and on a scale far beyond anything we’ve yet proved ourselves capable of, the detritus of civilization will be quickly devoured by the maw of deep time.
Geological time is deep beyond all comprehension. If you were to run a 26.2-mile marathon covering the entire retrospective sweep of Earth’s history, the first five-foot stride would land you two Ice Ages ago and more than 150,000 years before the whole history of human civilization. In other words, geologically and to a first approximation, all of recorded human history is irrelevant: a subliminally fast 5,000-year span is over almost as soon as you first lift up your heel, crammed entirely into the very end of an otherwise humdrum Pleistocene Ice Age interglacial.
This otherwise typical and temporary warm spell of the Pleistocene also is strangely given its own epoch, the so-called Holocene—quite unlike the dozens of similar interglacials that came before it—is the original sin of anthropocentric geology.
For context, let’s compare the eventual geological legacy of humanity (somewhat unfairly) to that of the dinosaurs, whose reign spanned many epochs and lasted a functionally eternal 180 million years—36,000 times as long as recorded human history so far. But you would never know this near-endless age was so thoroughly dominated by the terrible reptiles by looking to the rock record of the entire eastern half of North America. Here, dinosaurs scarcely left behind a record at all. And not because they weren’t here the entire time—with millions of generations of untold dinosaurs living, hunting, mating, dying, foraging, migrating, evolving, and enduring throughout, up and down the continent, in great herds and in solitary ambushes. But the number of sites within that entire yawning span, and over these thousands of square miles, where they could have been preserved—or that weren’t destroyed by later erosion, or that happen to be exposed at the surface today—was vanishingly small.
This astounding paucity can be explained by the fact that there just aren’t that many rocks that survived these extreme gulfs of time, over this vast province. And even among those rocks that did survive, and which are exposed today, the conditions for fossil preservation were rare beyond measure. Each fossil was its own miracle, sampled randomly from almost 200 million years of history—a few stray, windblown pages of a library.
So that’s what 180 million years of complete dominance buys you in the fossil record. What, then, will a few decades of industrial civilization get us? This is the central question of the Anthropocene—an epoch that supposedly started, not tens of millions of years ago, but perhaps during the Truman administration. Will our influence on the rock record really be so profound to geologists 100 million years from now, whoever they are, that they would look back and be tempted to declare the past few decades or centuries a bona fide epoch of its own?
An important thing to keep in mind about paleontology is that most fossil-bearing rock outcrops are marine—that is, they’re from the bottom of the sea. As a result, we have a much higher resolution of the history of life in the oceans than on land. That’s because the sea, for the most part, is where sediment goes to accumulate. Things fall apart on land and in general get destroyed by weathering and erosion, and get carried to the sea as sand grains and silt and in solution. If it weren’t for the ceaseless creation of new mountain ranges, the surface of the Earth would quickly be rendered flat. Yes, some cities, such as New Orleans, Dhaka, and Beijing, sit in subsiding sedimentary basins and, at first pass, seem promising candidates for preservation. But as the example of the dinosaurs shows, the chance that any city-swallowing delta deposit from a window of time only a few centuries wide would be lucky enough to be not only buried and preserved for safekeeping, but then subsequently not destroyed—in the ravenous maw of a subduction zone, or sinking too close to the cleansing metamorphic forge of Earth’s mantle, or mutilated in some mountain-making continental collision—and then, after all that, find itself, at a given point in the far future, fantastically lucky enough to have been serendipitously pushed up just enough so as to be exposed at the surface, but not too high as to have been quickly destroyed by erosion … is virtually nil. In the Grand Canyon, and over much of the Southwest U.S. (and even across the entire world), there’s a billion-year gap between rock formations. That history—that former forever—as marvelous as it may have been in that region of the world, will never be recovered.
But what would we leave on the seafloor, where most sedimentary rock is made, where most of the fossils are, and where we have a slightly better chance of recording our decades-long “epoch” in the rocks? Well, many marine sediments in the fossil record accumulated, over untold eons, from the diaphanous snowfall of plankton and silt, at a rate of little more than a centimeter per thousand years. Given this loose metric (and our current maturity as a species), a dozen centimeters of muck seems an optimistic goal for civilization.
A dozen centimeters is a pathetic epoch, but epoch or not, it would be an extremely interesting layer. It’s tempting to think a whisper of atomic-weapons testing would remain. The Promethean fire unleashed by the Manhattan Project was an earth-changing invention, its strange fallout destined to endure in some form as an unmistakable geological marker of the Anthropocene. But the longest-lived radioisotope from radioactive fallout, iodine-129, has a half-life of less than 16 million years. If there were a nuclear holocaust in the Triassic, among warring prosauropods, we wouldn’t know about it.
These trace isotopes may be the most enduring signals of humanity, together telling much of the story of our strange centuries, in only a few centimeters of ocean rock. They will speak, to those who know how to listen, of life-supporting geochemical cycles going haywire in an eyeblink of geological time, hinted at in small samples from our seam of strange strata that interrupts mile-thick formations of otherwise normal rock. Plastic, that ubiquitous pollutant of the oceans, might be detectable by analyzing small samples of this sediment—appearing, like many organic biomarkers in the fossil record, as a rumor of strangely heavy hydrocarbons. Unassuming peaks on a chromatograph would stand in for all of modernity. Perhaps, perhaps, if one was extremely lucky in surveying this strange layer, across miles of desert-canyon walls, a lone, carbonized, and unrecognizable piece of fishing equipment may sit perplexingly embedded in this dark line in the cliffs. Some “epoch” this.
What humans are doing on the planet, then, unless we endure for millions to tens of millions of years, is extremely transient. In fact, there exists a better word in geology than epoch to describe our moment in the sun thus far: event. Indeed, there have been many similarly disruptive, rapid, and unusual episodes scattered throughout Earth history—wild climate fluctuations, dramatic sea-level rises and falls, global ocean-chemistry disasters, and biodiversity catastrophes. They appear as strange lines in the rock, but no one calls them epochs. Some reach the arbitrary threshold of “mass extinction,” but many have no name. Moreover, lasting only a few tens of thousands to hundreds of thousands of years in duration, they’re all considered events. In our marathon of Earth history, the epochs would occasionally pass by on the side of the road like towns, while these point-like “events” would present themselves to us only fleetingly, like pebbles underfoot.
Fifty-six million years ago, the Earth belched 5,000 gigatons of carbon (the equivalent of burning all our fossil-fuel reserves) over roughly 5,000 years into the oceans and atmosphere, and the planet warmed 5 to 8 degrees Celsius. The warming set off megafloods and storms, and wiped out coral reefs globally. It took the planet more than 150,000 years to cool off. But this “Paleocene-Eocene Thermal Maximum” is considered an event.
A similar catastrophe struck 28 million years before, in the early Cretaceous, and again 60 million years earlier still in the Jurassic. And, again, 201 million years ago. And halfway through the Triassic, 234 million years ago. And 250 million, 252 million, and 262 million years ago. The first major mass extinction, 445 million years ago, took place in multiple pulses across a million years. An event. The second major mass extinction, 70 million years later, took place over 600,000 years—400,000 years longer than the evolutionary history of Homo sapiens. These are transformative, planet-changing paroxysms that last on the order of hundreds of thousands of years, reroute the trajectory of life, and leave little more than strange black lines in the rocks, buried within giant stacks of rocks that make up the broader epochs. But none of them constitute epochs in and of themselves. All were events, and all—at only a few tens of thousands, to hundreds of thousands of years—were blisteringly short.
Until we prove ourselves capable of an Anthropocene worthy of the name, perhaps we should more humbly refer to this provisional moment of Earth history that we’re living through as we do the many other disruptive spasms in Earth history. Though dreadfully less catchy, perhaps we could call it the “Mid-Pleistocene Thermal Maximum.” After all, though the mammoths are gone, their Ice Age is only on hold, delayed as it is for a few tens of thousands of years by the coming greenhouse fever. Or perhaps we’re living through the “Pleistocene Carbon Isotope Excursion,” as we call many of the mysterious global paroxysms from the earliest era of animal life, the Paleozoic. Or maybe we’re even at the dawning of the “Quaternary Anoxic Event” or, God forbid, the “End-Pleistocene Mass Extinction” if shit really hits the fan in the next few centuries. But please, not the Anthropocene. You wouldn’t stand next to a T. rexbeing vaporized 66 million years ago and be tempted to announce to the dawning of the hour-long Asteroidocene. You would at least wait for the dust to settle before declaring the dawn of the age of mammals.
The idea of the Anthropocene inflates our own importance by promising eternal geological life to our creations. It is of a thread with our species’ peculiar, self-styled exceptionalism—from the animal kingdom, from nature, from the systems that govern it, and from time itself. This illusion may, in the long run, get us all killed. We haven’t earned an Anthropocene epoch yet. If someday in the distant future we have, it will be an astounding testament to a species that, after a colicky, globe-threatening infancy, learned that it was not separate from Earth history, but a contiguous part of the systems that have kept this miraculous marble world habitable for billions of years.