Earth Sciences
Deep time, the geological record, and humanity as a planetary force
Edward O. Wilson was a biologist, not a geologist, and yet the earth sciences run through his work like a deep bass line, for no one can study the diversity and history of life without confronting the planet that produced it and the vast reaches of geological time in which it evolved. This chapter, opening the reader's final part on Wilson's reach across the disciplines, traces his engagement with the earth sciences: his evocation of deep time as the essential frame for understanding life, his reading of the geological record of catastrophe and recovery, his account of the co-evolution of life and the planet, and his insistence that humanity has itself become a geological force, opening a new and dangerous chapter in the Earth's history. Wilson approached these subjects always as a naturalist, interested in the earth sciences for what they reveal about the living world; but in doing so he drew biology and geology together, treating the history of life and the history of the planet as a single, inseparable story. The treatment of mass extinction as a biodiversity crisis is developed in Chapter 11, and humanity's ecological predicament in Chapter 19; here the subject is the geological and earth-system dimension of Wilson's thought.
Wilson's point of departure was deep time — the almost incomprehensible vastness of geological history, against which the whole human story is the briefest of moments. He was fond of inviting his readers to imagine traveling backward through evolutionary time, using vivid conceits to convey the immensity of the ages through which life has evolved and to shift the reader's perspective from the human timescale to the geological one. This temporal vision was, for Wilson, not a mere backdrop but an essential intellectual discipline: only by grasping the true depth of geological time can one understand the slow work of evolution, the accumulation of biological diversity over hundreds of millions of years, and the true gravity of the losses now under way. Against the backdrop of deep time, he emphasized, extinction takes on its full meaning as the permanent erasure of evolutionary achievements built up over eons — achievements that, once destroyed, will not be recovered on any timescale meaningful to humanity. And against that same backdrop, the human moment appears in its true proportion: the emergence of our species a very recent event in life's long history, and the rise of civilization more recent still, a mere eyeblink at the end of an immense geological day.
To convey the physical structure of the planet that life inhabits, Wilson offered memorable passages of earth-science exposition. He imagined a walk outward from the Earth's core through its successive layers to the surface, conveying the structure of the planet and the thin film of life that clings to its outer skin. He stressed that the biosphere — the zone of living things — is astonishingly thin relative to the bulk of the planet, a delicate membrane extending, at its full reach, only from the deep crust to the lower atmosphere, and that this thin living layer is all that separates the habitable Earth from the lifeless rock and gas of which the rest of the planet consists. This framing united geology and biology in a single vision: the Earth as a physical body of core, mantle, and crust, and life as a thin and precious phenomenon occupying only its surface. Wilson's evocation of the layered Earth served his larger purpose of instilling a sense of both the grandeur and the fragility of the living world — grand in its embeddedness in the vast physical planet, fragile in its confinement to that thin and vulnerable outer film.
Wilson traced the growth of life's diversity across this deep geological history as a long, uneven ascent. Biological diversity, he explained, has increased overall since the Cambrian period, building through the eons to reach its greatest height in the present — so that the world of today, for all the losses it is suffering, represents the peak of biodiversity in the whole history of life. He marked the great milestones of that ascent as they appear in the geological record: the eukaryotic revolution, the emergence around 1.8 billion years ago of complex cells with nuclei and organelles, which opened the way to all larger life; and the Cambrian explosion, roughly 540 million years ago, when animal body plans diversified with startling rapidity and the major groups of animals first appear in the fossil record. Through the hundreds of millions of years that followed, diversity rose and fell with the rhythm of origination and extinction, the standing richness of life at any moment representing the balance between the birth of new species and the death of old ones. Wilson stressed that this present peak of diversity is also, in a sense, fragile — the product of a long history that could be undone with terrible speed, its accumulated richness vulnerable in a way that its slow geological construction might lead one to forget.
Wilson also drew on the geological record to illustrate life's extraordinary resilience in the face of catastrophe, and here his favorite example was drawn from the recent geological past: the great eruption of Krakatau in 1883, which annihilated virtually all life on the island and left it a sterile ruin of ash and rock. In the decades that followed, Wilson recounted, life returned — plants and animals recolonizing the devastated island step by step, in a natural experiment in the reassembly of a living community that illuminated the very processes of colonization and equilibrium he had studied in his island biogeography (treated in Chapter 9). Krakatau demonstrated both the resilience of life, which recovers wherever the opportunity is given, and the sheer power of geological catastrophe to erase it. Across the far deeper reaches of the fossil record, Wilson stressed this same resilience on the grandest scale: despite the severity of the five great extinctions, life recovered each time, rebuilding its diversity over millions of years. Yet the very length of those recoveries carried the sobering lesson: life's resilience operates on geological timescales, offering no comfort to a species whose concerns are measured in generations, and no assurance that the particular living world we depend upon will survive the catastrophe now under way.
The heart of Wilson's engagement with the earth sciences was the geological record of mass extinction — the evidence, written in the rocks, of the great catastrophes that have periodically devastated life. He surveyed the five great mass extinctions revealed by the fossil record, from the end-Ordovician some 440 million years ago through the catastrophic end-Permian to the end-Cretaceous event that eliminated the dinosaurs, treating these as the defining episodes in the deep history of life. He examined the varied causes that geologists have implicated in these catastrophes — meteorite impacts, massive volcanism, changes in climate and sea level, the disruption of the planet's chemistry — noting that the end-Cretaceous extinction in particular is now widely attributed to the impact of a large asteroid. And he emphasized a fact of profound importance for understanding the present: that recovery from each of these mass extinctions took an immense span of geological time, between five and twenty million years, as life slowly rebuilt the diversity that catastrophe had destroyed. The fossil record, Wilson explained, reveals both the tempo of these ancient extinctions and the slowness of the recoveries, and it is this geological evidence that gives us our only real measure of what a mass extinction means and how long its consequences endure.
Wilson's own science was itself woven into this geological record, for the ants he had studied all his life left their own traces in the deep past. He and Bert Hölldobler recounted with evident delight the discovery of Sphecomyrma, the celebrated dawn ant preserved in amber from the Cretaceous period, a fossil that captured a primitive ant intermediate in form between the wasp ancestors of ants and their modern descendants. Sphecomyrma situated the origins of the ants in deep geological time, tracing the group back to the age of dinosaurs and confirming their evolutionary derivation from vespoid wasp stock, and it allowed Wilson and Hölldobler to reconstruct, from the evidence of the rocks and the amber, the immense antiquity of the social insects whose living descendants Wilson had spent his career pursuing. The dawn ant was, for Wilson, a vivid instance of how the fossil record connects the living world to the geological past, allowing the biologist to read in stone and amber the deep history of the creatures he studies in the field. It reminded him, and his readers, that every living species is the current endpoint of an immense evolutionary lineage stretching back through geological time, and that the ants underfoot are, in their way, living fossils of a history hundreds of millions of years deep.
From this reading of the geological record Wilson drew the conclusion that has become central to his legacy and to the earth sciences of our time: that humanity is now driving a sixth mass extinction, comparable in magnitude to the five great catastrophes of the geological past. The present episode of biodiversity loss, he argued, is not a routine fluctuation but an event of geological proportions, one that the naturalists and geologists of some distant future would read in the rocks as they now read the end-Permian or the end-Cretaceous. Wilson framed the present as the sixth great extinction, warning that a large fraction of the Earth's species could be lost within the coming decades unless the trend is reversed, and that this loss — like the losses of the geological past — would take millions of years to repair (the biodiversity dimension is developed in Chapter 11). What made the sixth extinction distinctive, and uniquely troubling, was its cause: for the first time in the history of the planet, a mass extinction was being driven not by asteroid or volcano but by the activity of a single species. Humanity had become, in effect, a geological agent, a force capable of altering the biosphere on the scale of the great catastrophes recorded in the rocks.
This recognition — that humanity has become a geological force — was the pivot on which Wilson's engagement with the earth sciences turned, and it aligned his thought with the emerging scientific concept of the Anthropocene, the proposed new geological epoch defined by human dominance of the Earth's systems. Wilson named humanity a planetary killer, a force driving extinctions at a rate not seen since the end of the age of dinosaurs, and he documented the many channels through which human activity now reshapes the planet: the transformation of the land surface, the alteration of the atmosphere and oceans, the disruption of the great biogeochemical cycles on which life depends. He presented his late work, culminating in Half-Earth (2016), as the completion of an Anthropocene trilogy — a sustained reckoning with the epoch in which human beings have become the dominant influence on the Earth's biosphere and geology. The concept of the Anthropocene captured precisely what Wilson had been arguing for decades: that human beings, once a minor species confined to a corner of Africa, had grown into a planetary power, altering the Earth on a geological scale and thereby taking upon themselves, whether they willed it or not, a geological responsibility for its future.
Among the geological forces now driven by humanity, Wilson gave increasing attention in his later years to climate change, which he identified as a rising threat of the first magnitude. Climate change, he argued, would intensify all the other drivers of extinction, compounding the destruction of habitat, the spread of invasive species, and the other pressures on the living world, and would rank among the gravest of the dangers confronting the biosphere in the coming century. He analyzed how the accumulation of greenhouse gases in the atmosphere — one of the principal ways in which pollution now alters the planet — was changing the global climate, and how that change would ramify through ecosystems already stressed by human activity. Wilson treated climate change not in isolation but as one component of the larger human transformation of the Earth system, a further expression of humanity's new role as a geological agent, and a further reason for the urgency that animated all his late work. The alteration of the planet's climate by human action was, for Wilson, perhaps the clearest single demonstration that our species had crossed a threshold — that we now influenced the Earth not merely locally, as every species does, but globally, at the level of the planet's fundamental physical systems.
Wilson's engagement with the earth sciences was never that of a detached observer, for it always issued in a moral and practical conclusion: the uniqueness and irreplaceability of the Earth. We have, he insisted, only one planet and one experiment — a single living world, the product of billions of years of geological and biological history, with no second Earth to which humanity might turn if this one is ruined. This was the ultimate lesson he drew from the earth sciences: that the Earth and its biosphere are the unique and unrepeatable outcome of an immense history, that the diversity of life now imperiled took hundreds of millions of years to evolve and cannot be quickly replaced, and that humanity, having become a geological force, bears an unprecedented responsibility for the fate of the only living planet we know. The vast timescales of geology, which might seem to dwarf human concerns into insignificance, carried for Wilson exactly the opposite lesson: precisely because the living Earth is the product of such immense stretches of time, precisely because its recovery from catastrophe takes millions of years, the damage now being done in the geological instant of a few human generations is all the more grave and all the more irreversible. To understand the earth sciences, for Wilson, was to understand the true stakes of the present moment.
In tracing the intersection of biology and the earth sciences, Wilson enlarged the frame of his life's work to its widest extent, setting the diversity of life against the deepest background of all — the history of the planet itself. He showed that the study of life cannot be separated from the study of the Earth, that the fate of the biosphere is a geological as well as a biological question, and that humanity's emergence as a planetary force represents a genuine turning point in the history not merely of our species but of the Earth. His was a vision in which the boundaries between the disciplines dissolved: the naturalist studying ant colonies and the geologist reading the strata were, in the end, engaged in a single enterprise, the understanding of the living planet across the whole sweep of its history. And from that enlarged vision Wilson drew his characteristic conclusion — that a species which has become a geological force must also become a geological steward, using its new and terrible power not to drive the sixth extinction to completion but to preserve the diversity of life through the dangerous passage of the present, so that the living Earth, unique in all the known universe, might continue its long history into a future worthy of its past.
The earth sciences thus provided Wilson with both his grandest perspective and his deepest sense of urgency. From the vantage of deep time, the living world appears as a vast and ancient achievement, the slow accumulation of biological diversity across geological ages, punctuated by catastrophe and painstaking recovery; and against that vantage, the human transformation of the planet appears as a sudden and violent rupture, a mass extinction driven for the first time by a conscious agent, unfolding not over the millions of years of the geological past but in the mere centuries of human history. To hold both perspectives at once — the immensity of geological time and the suddenness of the human impact — was, for Wilson, the beginning of wisdom about the human place in the history of the Earth. It humbled the human species, revealing it as a latecomer to a planet of unimaginable antiquity; and it charged that species with responsibility, revealing it as the first form of life ever to hold the fate of the biosphere in its hands. In drawing biology and the earth sciences together, Wilson gave his readers the fullest possible measure of what is at stake in the present moment: not merely the loss of individual species, but the wounding of a living planet four billion years in the making, by the one creature able to understand what it is doing.