Digging Up the Anthropocene

29 November 2017


Photograph by Ben Roberts.

A recent paper, The Working Group on the Anthropocene: Summary of evidence and interim recommendations, by Jan Zalasiewicz and twenty-four additional authors, considers the case for the formalization of the Anthropocene as a chronostratigraphic/geochronologic unit, i.e., a periodization of geological time. Since “Anthropocene” was proposed by Paul Crutzen in 2000 as a geological period marked by the impact of human beings upon the Earth, geologists have been attempting to determine if the geological record will someday bear the distinctive traces of human activity and whether (and this an interesting future contingent) geologists might someday be able to reliably locate and identify the Anthropocene boundary in the geological record. The emerging consensus is that there is, “…a clear synchronous signal of the transformative influence of humans on key physical, chemical, and biological processes at the planetary scale.” These synchronous signals are described as follows:

“A range of potential proxy signals emerged as potentially important during the analysis, for instance the spherical carbonaceous particles of fly ash (Rose, 2015; Swindles et al., 2015), plastics (Zalasiewicz et al., 2016), other ‘technofossils’ (Zalasiewicz et al., 2014a, 2016) and artificial radionuclides (Waters et al., 2015), changes to carbon and nitrogen isotope patterns (Waters et al., 2016) and a variety of fossilizable biological remains (Barnosky, 2014; Wilkinson et al., 2014). Many of these signals will leave a permanent record in the Earth’s strata.”

The Working Group on the Anthropocene: Summary of evidence and interim recommendations, by Jan Zalasiewicz, et al., Anthropocene, Volume 19, September 2017, Pages 55-60.

Will paleontologists of the future someday dig up technofossils, and from these technofossils attempt to reconstruct an entire technological infrastructure, much as we today reconstruct an extinct species from a single preserved vertebra or rib, and around the resulting organism we seek to reconstruct the entire vanished ecosystem in which that extinct species made its home?

Recently I was prompted to think about the Anthropocene from a paleontological perspective by a Twitter post by Ben Roberts, which included images of automobiles being degraded by weathering (these photographs are included in this post). In response to these images I wrote that I would like to see what the fossils of these automobiles would look like in ten million years. This caused me to think about the possibility of the artifacts of human civilization that might be preserved over geological scales of time. The signals mentioned above in the paper quoted all constitute microfossils that would begin to appear in the geological record for the first time with the advent of the Anthropocene, but I also wonder if larger artifacts might be preserved in the geological record.

Photograph by Ben Roberts.

The tissues of organisms — sometimes even soft tissues — are preserved in the geological record through several different processes. While it is unlikely that human artifacts would be fossilized by replacement and recrystallization or by adpression, it seems possible that technological fossils could be formed through permineralization or through casts and molds. It is easy to imagine that the hulk of an automobile, a train, or even an entire industrial facility might fill with sediment, and though the steel would rust away, that rust would be preserved in situ more or less in its finished form by the sediment hardening into sedimentary rock around it. A careful paleontologist thus might be able to excavate an entire locomotive by means of rust encased in sedimentary rocks.

Of course, fossils are rare, and most artifacts will be eroded away rather than fossilized. Moreover, technofossils are likely to be even more rare than natural fossils. Given our interest in our own past, and our technological abilities to recover artifacts, human beings will continually recover our own remains from the historical period. The fossil record that remains to be discovered will depend upon whether civilization is merely transient or whether it will prove to be enduring. In the case of civilization being a transient historical phenomenon (note that civilization could endure for another 10, 20, or 30 thousand years or more and still be “transient” from the perspective of paleontology), the process of recovering artifacts that would otherwise be fossilized will come to be end. There likely will be a few cases at least of human artifacts in sedimentary basins that eventually are preserved by some process or another. Human artifacts will ultimately be preserved in ice, in snow, in a glaciers, covered in sand on beaches and deserts, covered by landslides on land, as well as being preserved in the oceans, in deep, cold anoxic waters, as well as underwater covered in mud. There is a good chance that many ancient ships lost at sea have been entirely covered over by sand, mud, and silt, and are not likely to be located within our own historical period, thereby saved for far future paleontologists specializing in the excavation of technofossils.

Photograph by Ben Roberts.

Human beings have been building structures and leaving artifacts for thousands of years, of course — sufficient time for many of these structures to be abandoned, covered over, forgotten, and subsequently revealed once again to the light of day by archaeology. The extensive remains of the Indus Valley civilization were forgotten in this way, only to be rediscovered in the twentieth century, and the knowledge of the Minoan civilization had been reduced to mere legend when its palaces were eventually excavated. These remains have been subject to weathering and degradation, but some are in a remarkable state of preservation, though they have not been buried for millions of years, or subjected to the temperatures and pressures that result from being contained in geological strata. An insufficient time has passed for there to be a fossil record of human civilization, even though there is an archaeological record of human civilization.

Up until the industrial revolution, human industry was mostly carried out on a modest scale and resulted in little impact on the environment. Most materials employed were biodegradable and have disappeared over scales of historical time. I have previously observed that traces of Roman lead production have been preserved in the ice of Antarctica, and I would not be surprised to learn that silver processing at Potosí in the early modern period also left detectable traces. One might understand these examples as very early anticipations of later industrial processes carried out on a far larger scale. With the advent of technologies made possible by the systematic application of science to industry, new and unprecedented materials were invented and employed in industrial-scale applications. Some of these are the materials cited in the paper quoted above as the distinctive signals of the Anthropocene. While the recent paper cited above singled out a spike of artificial radionuclides, an earlier paper specifically mentioned plastics:

“Plastics are already present in sufficient numbers to be considered as one of the most important types of ‘technofossil’ that will form a permanent record of human presence on Earth.”

“The geological cycle of plastics and their use as a stratigraphic indicator of the Anthropocene,” by Jan Zalasiewicz, et al.

Contemporary industrial processes are sufficiently sophisticated to produce distinctively new technogenic materials (like Chernobylite) and on a scale to distribute the products of industry globally, and so to leave a planetary trace of human activity. It remains only for time, heat, and pressure to transform these distinctive traces into technofossils.

Photograph by Ben Roberts.

That the global deposition of a distinctive Anthropocene layer begins in earnest in the twentieth century (and specifically in the mid-twentieth century) is significant. The authors of the paper write:

“This mid-20th century level seems to serve best the prime requirement for a chronostratigraphic base of high-precision global synchroneity… Human activities only came to have an effect that was both large and synchronous, and thus leave a clear (chrono-) stratigraphic signal, in the mid-20th century. A wide range of evidence from this time indicates the rapid increase in scale and extent of global human impact on the planetary environment, also clearly recognizable from a wide range of synchronous stratigraphic indicators.”

The Working Group on the Anthropocene: Summary of evidence and interim recommendations, by Jan Zalasiewicz, et al.

It is interesting to note how this mid-20th century boundary (as geologists would call it; I might call it a “threshold”) corresponds to other boundaries (or thresholds) in human development. For example, in the Before Present (BP) time scale frequently employed in the sciences, the “present” for purposes of radiometric dating has been set as 01 January 1950, as radiometric dating became practical at about this time. A neat mid-century point of reference fit well with the actual date of the availability of the technologies of radiometric dating.

Recently in Radio Technology and Existential Risk I discussed what we may call “Sagan’s Thesis,” viz. that nuclear and radio technology are tightly-coupled, so that the invention of radio technology means both that the inventors of the technology can see and be seen in the cosmos, and that the inventors soon will be able to build nuclear weapons and so be enabled to destroy themselves. Radio, then, is both an existential risk and an existential opportunity, thus marking a threshold of technological maturity in the history of an intelligent species:

“Radio astronomy on Earth is a by-product of the Second World War, when there were strong military pressures for the development of radar. Serious radio astronomy emerged only in the 1950s, major radio telescopes only in the 1960s. If we define an advanced civilization as one able to engage in long-distance radio communication using large radio telescopes, there has been an advanced civilization on our planet for only about ten years. Therefore, any civilization ten years less advanced than we cannot talk to us at all.”

Carl Sagan, The Cosmic Connection: An Extraterrestrial Perspective, Chap. 31

While radio astronomy sensu stricto is not likely to leave any trace in the fossil record (though the wreckage of radio telescopes might be found), it will leave a lasting mark on civilization, and may (under some circumstances) transform a civilization. A changed civilization that endures for geological scales of time will leave a transformed trace of itself in the geological record. And for humanity, this change began near the mid-20th century boundary — about the same time as we began to use nuclear weapons, which is consistent both with Sagan’s Thesis and with a mid-20th century boundary for the Anthropocene.

The consilience of these several factors — planetary-scale anthropogenic impacts, radio technology, and nuclear technology (which includes both nuclear weapons and radiometric dating) — distinctively manifesting themselves on a global scale in the middle of the twentieth century, constitute “synchronous signals” not only for stratigraphy, but also for civilization on historical scales of time. In other words, the Anthropocene marks not only a geological periodization, but also a new stage in the development of civilization.

Train cemetery, Uyuni, Bolivia

In his original 1964 paper that introduced the idea of “types” of civilization, “Transmission of Information by Extraterrestrial Civilizations,” Kardashev defined a Type I civilization as a civilization at, “a technological level close to the level presently attained on the earth.” (Here I ask the reader to set aside imaginative characterizations of Type I civilizations that have been elaborated by individuals who have never bothered to read Kardashev’s paper.) As this paper was written in 1964, a mid-20th century boundary for the Anthropocene corresponds nicely with the level of technological development close to that attained by civilization at this time. We could, then, identify a Type I civilization with a civilization that produces an Anthropocene-like boundary on its homeworld (i.e., the equivalent of the Anthropocene for some other intelligent species but defined in an non-anthropocentric way).

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