The Age of Humans The Age of Humans

The Atomic Age Ushered In the Anthropocene, Scientists Say

Geoscientists have concluded that the Age of Humans officially began at the start of the nuclear age.

A mushroom cloud rises in the sky during an atomic weapons test in the 1950s. (Roger Ressmeyer/CORBIS)
smithsonian.com

Humans are living in a new geologic epoch, one that is largely of their own making, scientists say.

In a new study, published in this week’s issue of the journal Science, an international team of geoscientists concluded that the impact of human activity on the Earth is so widespread and persistent that it warrants formal recognition with the creation of a new geologic time unit, which they propose to call the Anthropocene epoch.

“We’re saying that humans are a geological process,” says study coauthor Colin Waters, a geologist with the British Geological Survey in the U.K. “We are the dominant geologic force shaping the planet. It’s not so much river or ice or wind anymore. It’s humans.”

The term “Anthropocene”–from anthropo, for “man”, and cene, for “new”–has been slowly gaining popularity as an environmental buzzword to describe humanity’s planet-scale influence since 2000, when it was popularized by the atmospheric chemist and Nobel laureate Paul Crutzen.

In recent years, however, there has been a growing movement amongst scientists to formally adopt the term as part of the official nomenclature of geology. Those who advocate this action argue that the current epoch dominated by humanity is markedly different from the Holocene epoch of the past 12,000 years, the time during which human societies developed and flourished.

The new study is not the first to propose a formal establishment of an Anthropocene epoch–Simon Lewis and Mark Maslin of the University of College London made a similar recommendation last year– but it is one of the most comprehensive to date. In it, Waters and his colleagues sought to answer whether human actions have left measurable signals in the geological strata, and whether those signals are markedly different from those of Holocene. The answer to both questions, the scientists say, is overwhelmingly yes.

The researchers conducted a review of the published scientific literature and found evidence for numerous ways that humans have changed the Earth to produce signals in ice and rock layers that will still be detectable millions of years from now. Among them: a preponderance of unique human products such as concrete, aluminum and plastics; elevated atmospheric levels of the greenhouse gases carbon dioxide and methane; higher levels of nitrogen and phosphorus in the soil from fertilizers and pesticides; and radionuclide fallout from above-ground nuclear weapons testing in the 20th century.

Humans have also indelibly shaped the biological realm by raising a few domesticated animals and cultivated crops to prominence while pushing other species toward extinction.

“I think these changes will be really obvious in the fossil record,” says Scott Wing, the curator of fossil plants at the Smithsonian National Museum of Natural History.

“Imagine the abundance of beef and chicken bones and corn cobs in sediments from now versus sediments deposited 300 years ago,” says Wing, who was not involved in the study.

Humans have also facilitated the mixing of species to a degree unprecedented in the history of the Earth, says Waters, who is also the secretary of the Anthropocene Working Group, an organization within the International Union of Geological Sciences.

“If we find a plant that’s nice to look at, within years we’ve transported it across the globe,” Waters says. “That is creating pollen signatures in sediments that are very confusing. Normally, you have to wait for two continents to collide until you get that kind of transfer of species, but we’re doing it in a very short period of time.”

As far as epochs go, the Anthropocene is a young one: Waters and his team argue that it only began around 1950 C.E., at the start of the nuclear age and the mid–20th century acceleration of population growth, industrialization, and mineral and energy use. In this, the group differs from Lewis and Maslin, who suggested the Anthropocene’s “golden spike”– the line between it and the Holocene–be set at either 1610 or 1964. The year 1610 is when the collision of the New and Old Worlds a century earlier was first felt globally, and the year 1964 is discernable in rock layers by its high proportion of radioactive isotopes–a legacy of nuclear weapons tests.   

“The Holocene was an abrupt event as far as geologists are concerned. And yet, we’re seeing changes that are even more rapid than that,” Waters says.

The Smithsonian’s Wing says he agrees that humans have changed the Earth sufficiently to create a distinct stratigraphic and geochemical signal. “I don’t think there is any doubt about it,” he says. “Not only is the signal distinct and large, it will persist for a geologically long amount of time, so it will be recognizable hundreds of thousands or millions of years into the future, should there be anyone then to look at the record.”

Interestingly, unlike the notion of climate change, for which scientific consensus was established long before public acceptance became widespread, Waters says members of the general public appear to be more willing to accept the idea of an Anthropocene epoch than some scientists.

 “Geologists and stratigraphers”–scientists who study the layers of the Earth–“are used to looking at rocks that are millions of years old, so many of them have a hard time appreciating that such a small interval of time can be a geologic epoch,” Waters says.

Both Waters and Wing say that in addition to being scientifically important, formally recognizing the Anthropocene epoch could have a powerful impact on the public perception of how humanity is changing the planet.

“There’s no doubt that when 7 billion people put their minds to doing something, they can have a big impact. We’re seeing that now,” Waters says. “But it also means that we can reverse some of those impacts if we wish, if we are aware of what we’re doing. We can modify our progress.”

Wing agrees. “I think the Anthropocene is a really important mechanism for getting people of all sorts to think about their legacy,” he says. “We humans are playing a game that affects the whole globe for an unimaginably long time into the future. We should be thinking about our long-term legacy, and the Anthropocene puts a name on it.”

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