The broiler chicken is the quintessence of the modern meat complex. In 1925 the average chicken brought to slaughter was 112 days old, ate 4.7 pounds of feed for every pound of liveweight chicken, and weighed 2.5 pounds when its neck was wrung. Today, an industrially raised chicken lives to 47 days, takes only 1.69 pounds of feed for every pound of chicken, and reaches 6.57 pounds. The bird is an unsteady scaffold for its ponderous breast. When they are finished growing, chickens are shoveled (or scooped by a harvester that has been compared to a Zamboni) into boxes and shipped to a processing facility, where Benjamin Ward Richardson’s vision of electronarcosis is carried to its mechanized extreme: The birds are strapped into conveyor belts, flipped upside down, plunged headfirst into water, then washed in an electrical bath. The stunned animals are then decapitated. Chickens are killed by the billions (about seventy-five billion every year), and poultry has become the world’s most consumed meat.
If curious extraterrestrial visitors were to reconnoiter Earth, they might well be struck by a planet that nurtures such an inordinate number of chickens. Chickens are the most numerous bird on the planet by a factor of ten, and there are about four of them for every one of us. We keep them warm, feed them, and tend to their prodigious piles of excrement. If evolution keeps score by counting genetic replication, then chickens have run away with the game, although their success is, in the words of one scientist, “the most heavily qualified of victories,” the fate of blinking alive just long enough to be turned into a nugget.
Whether or not aliens ever observe our curious symbiosis with the chicken, we can believe that someone will puzzle at it. Millions of years from now, the fossilized bones of the artificially evolved broiler chicken will be left behind in the Earth’s crust as a geological tracer of human dominance. Bird bones, in general, tend not to fossilize well. Our future geologists would need sensitive instruments and generous luck to detect the wave of avian extinctions since the late Pleistocene—La Brea storks and moas, dodos and auks, passenger pigeons and Mariana mallards, and more than a thousand others. The lesser prairie chicken will be invisible. But the sudden evolution of the improbably shaped and hyperabundant broiler chicken will be unmissable because the osseous debris of our fowl hunger—drumsticks and wing bones and oversized sternums—winds its way into landfills. There, in these gaping anaerobic middens, their bones mummify. They sink into the Earth, where they will abide in the rock until someday our dying sun swallows this little life-bearing mote of cosmic dust.
The broiler chicken will be an indelible geological signature of humanity, calling out to future eons, like graffiti scratched into a diner table, that we were here once, and we feasted.
Mostly hidden from our daily view, the machinery for making white meat—a chemical and metabolic system of planetary scope—will be a lingering trace of human presence in the annals of Earth history. The broiler chicken will be an indelible geological signature of humanity, calling out to future eons, like graffiti scratched into a diner table, that we were here once, and we feasted.
*
The broiler chicken could be the mascot for the Anthropocene. The Anthropocene, from “anthropo” (human) and “cene” (new), is the name of a new geological epoch, the proposed successor to the stable Holocene. The official timescale for Earth’s history is the stratigraphic chart, which looks like a labeled layer cake. Geologists use it to divide deep time into eons, eras, periods, and epochs based on changes that reflect changing conditions on Earth, its climate and chemistry. Our species was born in the cold Pleistocene, thrived in the comfortable Holocene, and may have plunged Earth into this new epoch, defined by our own dominance.
The idea of the Anthropocene is a prism to understand our influence on global biodiversity. The term itself is only about a generation old. It was born in 2000, at a meeting of the International Geosphere Biosphere Programme (IGBP) held in Cuernavaca, Mexico, when the Nobel Prize-winning atmospheric chemist Paul Crutzen asked to speak. The meeting’s chairman recalled the intervention: “As Paul began to recite with quiet urgency the extraordinary individual planetary changes beginning with James Watt’s invention of the steam engine in 1784, the litany began to take on a shape in the whole. The sum of sum of changes was change at the planetary level. This period of planetary change should be known as the beginning of a new Epoch: The Anthropocene.” Crutzen’s plea left the audience of scientists momentarily agape. But in the quarter century since, the conversation has never stopped.
The Anthropocene is a radical proposition. It claims that our 11,700-year interglacial, the Holocene, has ended and that we have irreversibly entered a new geological epoch. This new epoch is one in which the dynamics of the Earth System are shaped by human influence and in which our traces are etched permanently into the planet’s crust. Formally, the control of the Earth’s timescale is in the hands of the professional geologists—that is, the successors of Charles Lyell. Since Lyell’s day it has become a rather more bureaucratic endeavor to add an epoch to the geological record.
In 2024, after more than ten years of consideration, and contrary to the recommendation of its own Anthropocene Working Group, the Subcommission on Quaternary Stratigraphy voted against formally adopting the Anthropocene as our new epoch. This was the cautious route. But make no mistake: The caution of the geologists was and is excessive, and eventually, they will arrive at the conclusion that becomes more obvious by the day. Among scientists, scholars, and citizens, the term has become indispensable and inescapable. The Anthropocene has begun.
The debate over the stratigraphic timescale is more than a scientific kerfuffle. The Anthropocene is a paradigm for thinking about our place in Earth history. At its heart the concept reaffirms that Earth as we know it is an interlinked chain of the living and nonliving. Our planet is not an inert rock. It is a product of life, of the constant cycling of elements in and out of living beings. The sky is blue because of the oxygen put there by plants and bacteria. The fields and forests are green because green is the slice of visible light not absorbed for photosynthesis. Dirt is brown because it is a crowded, frothing skin on top of the plate beneath. Clouds condense around particulates breathed out by the biosphere. Now, one species dominates the living planet; our appetites, our social metabolism, and our by-products make us an agent of Earth-System change. The idea helps us recognize that humanity’s influence on biodiversity, now and into the foreseeable future, is inseparable from planetary-scale dynamics.
A geological epoch requires a start date, and while Crutzen initially suggested 1784, a near-consensus has since emerged that a more unambiguous stratigraphic marker lies around the mid-twentieth century, in the post-World War II era known as the Great Acceleration. The mid-twentieth century offers a clear dividing line in the geological record: Chicken bones and plastic pollution, disappearing forests, synthetic fertilizers, and the residues of nuclear bomb tests all mark a world transformed. Any far-future geologist sifting through sediment cores will detect a thin dusting of radioactive fallout as a precise time stamp of a world forever changed—an inexpungible technofossil boundary signaling humanity’s broader dominance.
The Great Acceleration refers to the dramatic, post-1950 surge in human population, economic growth, technological development, and resource consumption, all of which caused sharply intensified impacts on the Earth System—including its diverse biosphere. Take population: In 1900 there were about 1.6 billion humans; by 1950, around 2.5 billion; today, we are over 8 billion and counting. In other words, global population has more than tripled in a single lifetime. This demographic growth is premised on ecological deregulation, a breaking of the various barriers that hold population numbers in check. The control of infectious disease—through advances in medicine, sanitation, and public health—removed one of the oldest limits on our growth. In the mid-twentieth century, lifesaving technologies diffused globally. Without the ecological check of microbial parasites, humans proliferated. It is not that we started breeding like rabbits, as one observer put it, but rather that we stopped dying like flies.
Populations in nature are also regulated by their finite food supplies, and our control over infectious disease would have meant little without enough to eat. At the dawn of the twentieth century, fears of food scarcity were a rational nightmare. By century’s end, however, the specter of famine had largely receded (aside from tragedies of war and misgovernment, no small caveat). A global food crisis was averted thanks to rapid innovation. The Haber-Bosch process allowed us to capture inert nitrogen from the air and turn it into reactive fertilizer. This innovation—the mass manufacture of ammonia, vastly more efficient than scraping guano off remote islands or grinding mountains of bison bones—removed the most critical nutrient bottleneck in global agriculture.
Around the middle of the century, agronomists also developed high-yield, fast-growing varieties of staple crops like wheat and rice in what is known as the Green Revolution. Yields per hectare leaped in Asia, Latin America, and Africa. And finally came a massive surge of land brought under cultivation. In the postwar decades, humans seized ecosystems at breakneck speed—forests were felled, prairies plowed, wetlands drained. More tropical forest was destroyed in the late twentieth century than in any previous century, with roughly a sixth of the Amazon rainforest—an area the size of France—lost in just the past fifty years.
More food meant more humans and more of the animals we prefer to eat. Today, the literal weight of our species (approximately 60 million tons of carbon) and our domesticated mammals (mostly cattle and pigs, approximately 100 million tons) overwhelmingly exceeds that of all wild mammals (estimated at less than 10 million tons) on land. By one calculation, humans and our domesticated animals now account for about 94 percent of all terrestrial mammal mass on Earth, leaving only about 6 percent for all wild species. We have tipped the scales of the biosphere toward ourselves. And it is not just our bodies: The “stuff ” produced by human civilization now outweighs all living biomass on the planet. A recent study estimated that as of 2020, the mass of human-made materials (concrete, steel, asphalt, plastic, etc.) has reached about 1.1 teratons, exceeding the total dry weight of all living organisms (approximately equal to 1.0 teraton) on Earth.
Humanity has become an Earth-System force in the most utterly literal way—by moving a lot of earth. We push around the crust, reroute rivers, blast mountains, and layer the planet with artificial material. We displace more dirt and rock each year than all natural erosion processes. Mining operations have become ever more extensive as increasing amounts of overburden atop desired minerals and metals must be moved (for example, with all the easy gold fished out, an average of twelve tons of rock must be mined in order to produce the average four-gram wedding band). Year after year, we fabricate new houses, cars, roads, factories, skyscrapers. An average person now accounts for the production of their own weight in artificial matter every week—though, to put it mildly, there is no “average” person, and this mathematical sleight of hand smooths out our wildly unequal consumption habits.
In the Anthropocene, we have inverted the fundamental ecological predicament of our species: from scarcity to surplus, from hunger to glut.
What Newtonian mechanics was to the First Industrial Revolution, electromagnetism and chemistry have been to the Second Industrial Revolution, whose innovations have fueled the Great Acceleration. Fundamental science went hand in hand with applied technological innovation. Electricity turned on the lights, revolutionized manufacturing, and upended our evolved biorhythms. Telecommunication linked us together in an ever-louder, ever-wider web of chatter. The internal combustion engine finally ended the four-thousand-year reign of the horse.
Above all, advances in chemistry have given us a different kind of control over the rest of animal life. The examples of vitamin D and synthetic fertilizer already point in this direction. We still tend to underestimate chemistry, in part because the true history of the twentieth century reads like the fine print of a shampoo bottle. At the risk of discouraging readers, this chapter’s protagonists will include cholecalciferol, ammonia, neonicotinoids, polyethylene, 17α-methyltestosterone, and diclofenac. (Certainly, if any of these are actually in your shampoo, change brands.) We need deep perspective to see how unusual these compounds are.
Nature, over four billion years of evolutionary history, has learned to build some remarkable molecules. Biological evolution is a blind but tireless research chemist. Some of its engineering feats—the ballet of protein folding, the ribosome’s efficiency, the sewing of sugar from sunlight—we can only admire. But evolution is constrained; it must build incrementally on what already exists, solving a Rubik’s cube of organic chemistry one random twist at a time. By contrast, we dive to the atomic level and start fresh. We are catching up and, in some ways, surpassing nature with our synthetics—plastics, pesticides, and pharmaceuticals. Chemistry is a godlike craft, both generative and destructive.
One strange index of these powers can be registered by counting the mineral diversity on planet Earth. Billions of years ago, this little corner of the universe contained only a dozen or so primary minerals—raw building blocks forged in the hearts of ancient stars and cast into the cosmos by supernovae. These dust grains gathered to form the earliest planetesimals. Inside those embryonic worlds, heat and pressure gave rise to more complexity—perhaps 250 distinct minerals, which fused to make the early Earth. Then, during our planet’s infancy, volcanic upheaval and deep-earth alchemy created more than a thousand new minerals. Then came life. Microbes began chewing and spewing, transforming the chemistry of oceans and rocks. Photosynthesis pumped out oxygen. Life remade geology.
By the time multicellular creatures arrived, our living planet boasted nearly five thousand minerals—an abundance unmatched in our solar system. And then there was us. The International Mineralogical Association—gatekeeper of the rock registry—insists that synthetic minerals don’t count in its official tally (it recognizes only “natural” or “geologically occurring” stable inorganic crystals). But a mineral is a mineral, whether grown in a supernova or in a lab. In objective terms we have added more than three hundred thousand minerals to the Earth. Wafers of monocrystalline silicon. Yt-trium aluminium garnet in lasers. Boron carbide, as hard as anything this side of diamond, embedded in body armor. These, too, will linger in the crust, enduring witnesses to human agency.
Our mastery of synthetic chemistry is akin to a second control of fire, a biological and geological milestone in Earth history. Synthesis also guzzles energy, and energy consumption is the foundation of modern growth, a hallmark of the Great Acceleration. Coal fueled early industrialization and was soon complemented by the hydrocarbons oil and gas: fossil sunlight captured by ancient plankton and stored as fluids. Gradually, contributions from nuclear fission and solar-, water-, and wind-power have augmented our supply. Since 1950, humanity has consumed twenty-two zettajoules of energy. To put it more intuitively, in the last three generations our species has used more energy than we did in the entire Holocene, stretching over more than ten millennia. In whatever year you are reading this, I assure you it represents the annual peak of human energy consumption so far.
In the Anthropocene, we have inverted the fundamental ecological predicament of our species: from scarcity to surplus, from hunger to glut. This transformation has made us a dominant force in the Earth System. It is not difficult to see how human influence on the planet has rewritten its story of biodiversity…: The annihilation of the megafauna reshaped carbon and methane flows; deforestation helped to postpone the next ice age; industrialization burned primeval forests. But these were mere hints and premonitions of the kind of sway that humans now hold. And that dominance is new, in no way requiring Lyell’s quirky sense of deep time to justify it as kainos (-cene, “recent”). In only a few human generations, the Great Acceleration has tipped the planet into a new geological epoch.
The Anthropocene will mark a permanent geological and paleontological boundary in the rock record. Future geologists will see, everywhere, evidence of our Earth-System agency—the physical traces of a planet dominated by one species. Future paleontologists will recognize a decisive turning point in the evolutionary record. That there will be a fossil signal of the Anthropocene is already certain and irreversible, a fait accompli; what exactly that signal will say is uncertain and still to be decided.
Whether or not we precipitate a new mass extinction, our influence on the biosphere is part and parcel of the Anthropocene, something systemic and planetary. It reaches from pole to equator, reshapes the conditions of life on land and in the oceans, and bears on the fate of creatures great and small.
_______________________________
From The Last Animal: Human History and the Fate of Life on Earth from the Ice Age to the Sixth Extinction by Kyle Harper. Copyright © 2026. Available from Princeton University Press.