“An anthropogenic marker horizon in the future rock record”

CITATION:
Corcoran, P.L., Moore, C.J., and Jazvac, K. 2014. GSA Today, Vol. 24, No. 6, pp. 4-8.
ON-LINE AVAILABILITY:
ABSTRACT:
Recognition of increasing plastic debris pollution over the last several decades has led to investigations of the imminent dangers posed to marine organisms and their ecosystems, but very little is known about the preservation potential of plastics in the rock record. As anthropogenically derived materials, plastics are astonishingly abundant in oceans, seas, and lakes, where they accumulate at or near the water surface, on lake and ocean bottoms, and along shorelines. The burial potential of plastic debris is chiefly dependent on the material’s density and abundance, in addition to the depositional environment. Here, we report the appearance of a new “stone” formed through intermingling of melted plastic, beach sediment, basaltic lava fragments, and organic debris from Kamilo Beach on the island of Hawaii. Agglutination of natural sediments to melted plastic during campfire burning has increased the overall density of “plastiglomerate,” which inhibits transport by wind or water, thereby increasing the potential for burial and subsequent preservation. Our results indicate that this anthropogenically influenced material has great potential to form a marker horizon of human pollution, signaling the occurrence of the informal Anthropocene epoch.

Walk into any Target, Walmart, or really any store, and look around. Everything you see will move out of the store, through the consumption cycle, and into the garbage, wherever that may be. The organic matter degrades in relatively short order. But the plastics do not. Imagine all those clamshell packages. All the plastics surrounding the pallets of endless stacks of plastic water bottles piled up to the rafters of the great “big-box” stores. Plastic chairs, plastic toys, plastic bags. Stand in the center of the store and imagine it all in the dump. Or in the ocean. In bellies of whales, in the Pacific gyre, composing the largest accumulation of plastic on the planet.

Paul Crutzen’s suggestion of a new epoch—the Anthropocene—has spawned arguments over the nature of the marker for this new epoch. In the arcane world of what geologists call “stratigraphy,” proposing a new interval of geologic time is no small matter. It begs the question of the nature of time—the passage of events. Celestial events (eg. the Sun rising) awake us in the morning. Celestial events mark the timing for Easter, Ramadan, and other observances.

So how is time marked in the geologic record? By the passage of significant events—usually related to major faunal/floral turnovers (extinctions). Where marked by fossils this is relatively easy. If not marked by fossils, then global biogeochemical shifts can work. Markers suggested for the Anthropocene have included the Cs-137 spike denoting the nuclear age, or perhaps it will be a marine dissolution horizon resulting from global ocean acidification related to carbon emissions. Or the perturbation of the nitrogen cycle, or analogous chemical signal related to the breaching of a “planetary boundary.”

Or perhaps it is the Time for Plastic. In this short paper, Corcoran et al. demonstrate what used to be discussed in jest—that our time will be marked by plastic. Reading it reminded me of a geological field trip I took over 20 years ago. The trip was to a beach setting, to study modern carbonate depositional environments. What I recall most about it was not the cobbles of brain coral awash but the flotsam and jetsam of civilization— in the form of doll parts, toilet seats, hypodermic needles, and yes—plastic bags (some filled with contraband), piled up so high as to obscure the coral debris. Corcoran et al. illustrate that, beyond the now widely recognized piles of plastic debris on land and in the oceans, this debris is now forming lithified sediment—an event layer in the geological record.

Is plastic a problem? Actually, it’s extremely useful—plastic has transformed our lives. It’s lightweight yet strong, and can be used in place of other materials derived from resources harder to extract. Plastics help preserve and transport food, and reduce fuel use by providing lightweight containers. And on and on. So the problem is not necessarily plastic per se, but the life cycle of plastic—or rather that there IS no “cycle” to its life. If plastic were recycled, there would be no issue, and it is eminently recyclable.

We are creative animals. Surely we can do better than to mark the rise of Man with the ignominy of (unrecycled) plastic.


FURTHER READING:
Rockstrom, J., and 28 others. 2009. “A safe operating space for humanity.” Nature, v. 461, pp. 472-475. In this paper Rockstrom presents the concept of “planetary boundaries.”
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