Scientists say human activity has so fundamentally altered the geology, atmosphere and biology of the earth that it has entered a new geologic epoch known as the Anthropocene.
On Tuesday, members of the Anthropocene Working Group (AWG) presented evidence of that shift from a lake in Ontario, Canada — evidence they believe can help pinpoint a start date for the new human-driven epoch.
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“It’s quite clear that the scale of change has intensified unbelievably and that has to be human impact,” said University of Leicester geologist Colin Waters, who chaired the AWG.
He explained that human activity is “no longer just influencing Earth’s sphere, it’s actually controlling” it.
Tuesday’s announcement centred on discoveries made in Lake Crawford, located approximately 60km (37 miles) west of Toronto.
Sediment deposited at the bottom of lakes can provide scientists with a geological record of changing environmental conditions.
While the team of scientists collected core samples from 11 other sites, Lake Crawford’s exceptional depth allowed sediment to float downward relatively undisturbed, creating layers that can capture distinct environmental markers.
Scientists were therefore able to document a “golden spike” among its layers of sediment: a dramatic and, at least in geological terms, sudden change in the conditions of the earth.
Part of that “spike” was evidenced by the presence of plutonium in the lake sediment. Plutonium rarely occurs naturally, leading scientists to conclude it came from nuclear testing in the 1950s.
Waters, the geologist, said it was a “clear marker” for the shift to the Anthropocene, the age of humans. He and the other members of the AWG have proposed naming the start of the new epoch between 1950 and 1954.
If accepted, the Anthropocene — derived from “anthropo-“, meaning “human” — would mark the conclusion of the Holocene, the epoch that spanned the last 11,700 years.
“Clearly the biology of the planet has changed abruptly,” Waters added. “We cannot go back to a Holocene state now.”
But the idea of an Anthropocene epoch has yet to be formally recognised. First proposed by Nobel Prize-winning chemist Paul Crutzen some 20 years ago, the Anthropocene has been hotly debated: Scientists disagree over when it might have begun or even how to define it.
The AWG plans to submit its proof to the International Commission on Stratigraphy, which is tasked with naming geological eras of the earth’s history. Several scientific committees must still vote to recognise the Anthropocene before it is commonly accepted.
John Holdren, a former United States White House science adviser, is among those advocating for a much earlier start date to the Anthropocene. While he was not a member of the AWG, he nevertheless agrees that human behaviour is changing the earth in unexpected ways.
“The hubris is in imagining that we are in control,” Holdren told The Associated Press. “The reality is that our power to transform the environment has far exceeded our understanding of the consequences and our capacity to change course.”