The doom-sayers and gloom-gatherers among us have gotten pretty familiar with the Anthropocene; that evocative epoch some scientists say we’re living in right now—adios, Holocene. It defines the time where man began to fundamentally change the face of the planet. When biologists talk about the human-caused mass species extinctions, they may nod to the the Anthropocene. When climate scientists talk about the concentration of carbon dioxide in the atmosphere now influencing weather events the world over, they might mention the Anthropocene.But there’s one particularly notable band of holdouts: geologists. As we learn in Paul Voosen’s wonderful report on how geologists are engaging this notion of a new epoch—which was pretty much whipped up by a single atmospheric chemist, the Nobel laureate Paul Cruzen, around the turn of the century—those students of rock and earth are skeptical that we humanfolk have made a significant enough dent in the planet to warrant our own epoch.And indeed, such questions have been posed before; here, for instance, the Geological Society of America wonders: Is the Anthropocene an issue of stratigraphy or pop culture?It’s a good question. After all, though human beings undoubtedly dominate the planet and its resources right now, if we were to be wiped off the face of it all, we’d leave relatively little trace. Things would return to their pre-human status pretty quickly, as Alan Weisman demonstrated in his nonfiction thought experiment ‘The World Without Us’:So. Even though we’re killing all the world’s animals and transforming its climate, there’d be precious little human residue left for the alien excavators who happen upon earth in the year 377 million AD or whatever. Most of our impressive-looking stuff—our cities, or monuments, our harbors—would vanish without a trace in a matter of tens of thousands. This certainly wouldn’t last.And yet the geologists are interested. There are a number of distinctly human-made impacts that they think might come to define the Anthropocene, and they’re venturing some conjecture. Here’s what’s in the running so far as the stuff the epoch of man is made of:
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- Runaway climate change. If we don’t address rising carbon levels, and the ice caps melt, or we trigger one of the ‘feedback loops’ (like methane in the permafrost), then we’ll likely have some bona fide global indicators that man planted his conniving flags around the planet.
- Nuclear detritus. Though not the stuff you’d think; plutonium only hangs around for a bit with a half life of 22K years. No, the geologists are more interested in the spread of iodine-129. It has a half-life of 15 million years, so it would be quite detectable even 200 million years into the future. Voosen writes that “the global distribution of this detritus has made atmospheric testing a strong candidate for the Anthropocene’s start. It helps that the testing coincides with what IGBP scientists call the Great Acceleration: the postwar period when oil- and coal-fired growth took off like a rocket throughout the world. By 1950, CO2 emissions sat at 315 parts per million, barely outside the Holocene’s normal variation; that soon changed. Synthetic fertilizer become common in farming. Dam construction boomed.”
- Fossil fuels mining. There are 568,000 abandoned mines in the U.S. alone, and millions more around the world.
- Chemicals, radioactive particles, and pollutants trapped in runoff that accumulates at river mouths and deltas. Geologists wager that the stuff being trapped in places like the Mississippi around the world may make for a permanent marker.
- Nitrogen. We’ve changed the global nitrogen cycle; scientists have already confirmed that. If there’s a durable trace …