Where, in my essay, I emphasized the potential transience of civilization, Wing and colleagues on the Anthropocene Working Group emphasize the eternal mark left on the biosphere, whether our civilization is transient or not. This, they argue, is the Anthropocene.
“It doesn’t stake out a hopeful future and it doesn’t stake out a catastrophic future,” Wing said. “It just says that if you want to be a sentient species you have to reckon with the degree to which you have already changed things.”
And that change—whether through tens of thousands of years of human-driven extinctions, our spreading of invasive species across the face of the Earth, converting half of its land surface to farmland, or warming the planet and souring the seas—is undoubtedly profound.
But such dramatic changes don’t always define epochs in the rock record. True, the asteroid at the end of the Cretaceous and the chaotic rocks it left behind mark both the instantaneous end of the age of dinosaurs and the beginning of the 10-million-year-long Paleocene epoch—the beginning of the age of mammals. And it is a decent (if, to this point, still far more devastating) analogue to humanity’s lightning-fast impact on the living world. But consider the disruption inflicted on the planet by the rise of land plants more than 300 million years earlier. In the Paleozoic, land plants conquered the continents and geoengineered the planet, possibly contributing to, or even causing, at least 10 extinction pulses over 25 million years, including one of the worst mass extinctions in Earth history. Land plants profoundly and permanently altered Earth’s geochemical cycles, underwrote the flourishing of all subsequent life on land, and might have sequestered so much carbon dioxide that they kicked off a 90-million-year ice age.
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“The evolution and spread of land plants across the Earth was far greater than the human impact ever will be, and I don’t see any drive to define a [stratigraphic] unit based on that,” said Stan Finney, the outgoing chair of the International Commission on Stratigraphy, the governing body decides what is and isn’t an epoch. Finney famously dislikes the idea of the Anthropocene, referring to it as “the few millimeters of sediment deposited since 1945.”
“Isn’t the [Anthropocene] anthropocentric?” he asked at the 2015 Geological Society of America annual meeting, proposing instead that we recognize the term on the same footing as “the Renaissance,” rather than bestow it with the official sanction of geology.
Wing thinks the criticism by Finney and others misses the point. Yes, geology—a field that has developed over centuries, and has accumulated rules, and rules of thumb, as haphazardly as keepsakes in an attic—is inconsistent. There isn’t some Platonic “epoch” out there waiting to be cross-referenced with the various layers of Earth’s rocks. This is because naming units of sediment is a fundamentally human endeavor. We decide what to emphasize, and Earth history gets divided up insofar as such divisions are useful or important to scientists, and to the broader public.