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Did the Anthropocene begin in the 1950s?

Anthropocene: Old image showing a mushroom cloud erupting over a body of water.
Nuclear test at Bikini Atoll, 1946. Pointing to a layer of plutonium in a lakebed in Canada, experts suggested in 2023 that Earth began a new epoch in the 1950s. They call it the Anthropocene, or Age of Humans. Image via U.S. Dept. of Energy.

Anthropocene, the Age of Humans

The current geologic epoch is called the Holocene. That’s the name given to the last 12,000 years (or so) of Earth’s history, since the last major Ice Age. But, for more than two decades now, scientists have been speaking of a new geologic epoch: the Anthropocene, or Age of Humans. And, on July 11, 2023, an interdisciplinary research group called the Anthropocene Working Group pointed to new evidence in the sediments of Crawford Lake, Ontario, Canada, suggesting the Age of Humans has begun.

It was the biologist Eugene Stormer and the chemist Paul Crutzen who first introduced and popularized the word Anthropocene in the year 2000. It’s derived from the Greek words anthropo, for man, and cene for new. It’s logical to think that a new Age of Humans has begun. After all, as now seems obvious, humans are affecting Earth in unprecedented ways, including changing Earth’s climate.

But what does it take to establish a new epoch of geologic time?

A lot, as it turns out.

Identifying a golden spike

Have humans changed Earth enough to impact the geologic record? That change is the stated required for establishing a new epoch, according to scientists affiliated with the International Commission on Stratigraphy, of which the Anthropocene Working Group (established in 2009) is a part.

What is stratigraphy? It’s the branch of geology concerned with the order and relative position of strata (rock layers) and their relationship to the geological time scale.

So, to declare an Age of Humans, scientists would need to be convinced of a human impact visible within Earth’s rocks layers. And for some years, scientists have proposed that we should be able to find that impact in the form of a layer of plutonium laid down in rock after nuclear weapons testing in the 1950s. Scientists call that a golden spike – evidence in Earth’s sediment layers – clearly demarcating one geologic epoch from another.

Out of many possible sites, geologists picked Crawford Lake in Ontario to look for the golden spike. Specifically, they chose the lake because of the clear annual deposits in its sediments. It’s a small body of water, just about half the size of a football field. But also, it’s about 80 stories deep. It lies southwest of Toronto and west of giant Lake Ontario.

And now, says the Anthropocene working group, the golden spike – the telltale plutonium layer – has been found in the lake.

A spiral chart marked off with the names of eras, periods and epochs.
The Geologic Time Spiral, in which geologists separate time into eras, periods and epochs. Image via the U.S. Geologic Survey.

What are some other golden spikes?

A more familiar and historic example of a golden spike is the one that indicates the end of the Cretaceous Period and the start of the Cenozoic Era.

Indeed, some 65 million years ago, an asteroid struck Earth, bringing about the extinction of the dinosaurs. That impact led to a layer of iridium in the rock record around the world.

And to be sure, in the late 1970s, scientists discovered this golden spike of iridium.

The great acceleration

Humans didn’t exactly wham suddenly into Earth, as an asteroid might. Rather, our impact built slowly, over millions of years of human evolution. However, in the last century – and especially around mid-20th-century – our human population size, and subsequently our impact, began to increase. As a result, some refer to a great acceleration that began on Earth in the 1950s. That’s a term used to describe human impacts intensifying and beginning to happen globally, not just locally.

In addition, testing of nuclear weapons began in the late 1940s and into the 1950s. It led to radioactive elements – such as plutonium, a rare element on Earth – showing up in the geologic rock layers.

And some scientists point to other ongoing signs of the Age of Humans, which will ultimately find their way into the rock record. These include plastic pollution, soot from power stations, high levels of nitrogen and phosphate from artificial fertilizers and more.

University of Leicester geologist Colin Waters, a member of the Anthropocene Working Group, said:

It’s quite clear that the scale of change has intensified unbelievably and that has to be human impact.

Dissenting opinions on the Anthropocene

The Anthropocene age is not official yet, and may never be. After its approval by the Anthropocene Working Group, it still needs to be approved by three other groups. Those groups are the Quaternary Subcommission, the International Commission on Stratigraphy and the International Union of Geological Sciences. According to Erle Ellis on Twitter, the next vote will be within two months, and the final vote will be next year.

Some have argued that the word Holocene is good enough to describe our human impact and that we don’t need the new term Anthropocene.

On the other hand, scientists outside of geology also feel they have a stake in the naming of a new epoch. As paleoecologist Jacquelyn Gill said on Twitter:

If the Anthropocene is to be used by everyone in the way the Anthropocene Working Group hopes, they should have included social scientists, environmental historians, philosophers, ethicists, human geographers, activists and others who are also stakeholders in the academic definition of ‘Anthropocene.’

Humans changing Earth

One thing is clear from the comments on our many articles about Earth here at EarthSky: that is, some people are uncomfortable at the idea that humans have any real impact on the planet at all.

But even just a quick look at the Earth at night from space shows millions of twinkling lights that would beg to differ.

According to NPR, former U.S. White House science adviser John Holdren thinks the proposed start date of the Anthropocene should be much earlier. And while we may have triggered the Anthropocene, he also said:

The hubris is in imagining that we are in control. The reality is that our power to transform the environment has far exceeded our understanding of the consequences and our capacity to change course.

Naomi Oreskes of Harvard University and a member of the Anthropocene Working Group said:

If you know your Greek tragedies you know power, hubris and tragedy go hand in hand. If we don’t address the harmful aspects of human activities, most obviously disruptive climate change, we are headed for tragedy.

Bottom line: A scientific working group declared that a new epoch – the Anthropocene – began in 1950, with evidence from a lake in Ontario, Canada.

Via Nature

July 13, 2023

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