Nope. Humans have influence, a “profound influence,” researchers say, and on a planetary scale. As a testament to that fact, two geologists writing in the journal “Nature” Wednesday added their voices to the call for the establishment of a new geological epoch, the Anthropocene, with a suggested start date of either 1610 or 1964.
“The impacts of human activity will probably be observable in the geological stratigraphic record for millions of years into the future,” authors Simon Lewis and Mark Maslin said. “Which suggests that a new epoch has begun.”
Scientists have been classifying stages from Earth’s history since the turn of the 19th century, back when geology was a gentleman’s extracurricular conducted over dinner at London taverns. A mining surveyor named William Smith had recently concluded that the stripes of varying types of rock visible in mountains, canyons and outcroppings could be interpreted as evidence of distinct moments of geological time, laid down one on top of the other over the course of millennia. Although Smith spent much of his life in debt and obscurity, his enthusiasm for dividing up geological history based on the layers of rock beneath his feet seemed to catch on. Now we call it stratigraphy.
Modern stratigraphy has us in the Holocene (“entirely recent”) epoch, which began at the end of the last Ice Age 11,700 years ago. That is the last time the Earth saw significant environmental change on a global scale, the kind that leaves evidence in its own stratum of the geological record. At least, that’s what the average high school geology textbook will tell you.
There are stratigraphers who feel differently. Since 2000, some have argued that the planet is being subjected to significant, world-wide change of the kind that characterizes the beginning of a new epoch. Usually such shifts are attributable to continental movement, major atmospheric changes, asteroid impacts and the like, but this time the change appears to be caused by us.
Currently, the possibility of formalizing the new epoch is being reviewed by the Working Group on the “Anthropocene,” a project of the International Union of Geological Sciences established in 2009. Some time next year, they hope to issue a recommendation to the Subcommission on Quaternary Stratigraphy (true to their 19th century roots, geologists still like to make decisions by committee — though this one won’t be meeting in a London pub), launching the first of several steps in establishing an Age of Man.
Several other studies have pushed for a designated Anthropocene and offered up possible start dates. But Lewis, the lead author of the Nature paper, said his is the first to survey all those suggestions and subject them to the kinds of stratigraphic standards that originated with William Smith.
“We wanted to see whether we could find a global environmental change that is captured in the geological record, something that is going to be preserved, that signals a shift in the whole earth system,” he said in a phone interview.
Lewis and Maslin (neither of whom are members of the working group) surveyed nine prominent proposals for the Anthropocene start date, along with the stratigraphic markers that would allow geologists of the future to identify the era in the rock record. Some were dismissed for lacking a clear “inflection point” — a moment at which it was evident that everything changed. One of the most common suggested start dates — the Industrial Revolution — was rejected because the changes caused by industrialization happened in different places at different times, so markers of the period (such as ice core records of carbon dioxide and lead use) are scattered and inconclusive.
In two cases, the duo found a “golden spike,” a clear signal of environmental change that can be found in the geological record worldwide. The first happened in 1610, when ice cores show a sharp, measurable dip in levels of atmospheric carbon dioxide. This shift was caused by the rapid destruction of American farming societies (farms are big producers of carbon) in the collision of the Old and New Worlds. The sudden appearance of American species in the European fossil record — and vice-versa — offers up more evidence of a permanent global change.
The second “golden spike” is the increased levels of Carbon-14, fallout from nuclear activity, which peaked around the year 1964. Much like the carbon dioxide dip, the Carbon-14 spike happened pretty much instantaneously worldwide and is a signal of a massive, irreversible global change: the “Great Acceleration” in human population growth and technological advancement that began in the 1950s.
Jan Zalasiewicz, who leads the Anthropocene working group, said he is especially intrigued by Lewis and Maslin’s 1964 suggestion. The mid-20th century is full of the kind of human activity that leaves geological traces, not only nuclear testing but also the creation of plastics, the release of carbon dioxide, the pouring of miles and miles of concrete.
“All of it eminently fossilizable,” he said.
With a geologist’s eye for time’s vast expanse, Zalasiewicz can envision a future in which the micro particles of a fleece jacket’s plastic fluff can be found preserved in ocean sediments, much the way scientists study the fossilized remains of ancient sea creatures today
But in defining the Anthropocene, he’s not thinking that far ahead.
“We just need it to last for at least 10 years,” he said.
If that seems short, Zalasiewicz will remind you that this has never been done before. Previous epochs have all been established with millennia of hindsight. But pro-Anthropocene geologists are attempting to classify a period they’re currently living through — one that’s changing every day.
There are politics to consider too. In their paper, Lewis and Maslin caution that the chosen start date for the Anthropocene could “affect the stories people construct about the ongoing development of human societies.” Choosing 1610 could highlight social concerns about colonialism and globalized trade, whereas the 1964 option might paint a picture that technological advancement is propelling humanity toward planetary destruction.
Meanwhile, Zalasiewicz has to grapple with other geologists. In a discipline that measures time in the hundreds of thousands of years, the notion of establishing a new epoch based on but a few centuries of geological evidence can seem positively impetuous.