A team of scientists have a new contender for determining the precise date that we entered the so-called Anthropocene: A lonely spruce tree on an island 400 miles south of New Zealand.
Scientists are searching for a “golden spike” to help define the precise start of the Anthropocene Epoch, a human-driven era that would follow the 12,000-year Holocene, which began with the rise of human civilization at the end of the last Ice Age. Potential dates range from the rise of agriculture 10,000 years ago to the peak of the “bomb spike” of artificial radionuclides in the middle of the 20th century, or even later to the spread of industrial chemicals.
The new study, published Monday in Scientific Reports, places the start date near the end of the timeline, between October and December 1965. Conducted by members of the 2013-2014 Australasian Antarctic Expedition, the study suggests that a single Sitka spruce (Picea sitchensis) could mark the start of the Anthropocene, due to the clear radioactive bomb record from the 1950s and 1960s in its wood—peaking in 1965 just after atomic bomb tests were banned.
According to researchers Chris Turney, Jonathan Palmer, and Mark Maslin, who all participated in the study, the tree’s remote location is key.
“The problem from a geologist’s point of view is most of the records of this spike in radioactivity (for example preserved in lake sediments and the annual growth of tree-rings) have been reported from the Northern Hemisphere where the majority of the tests took place,” they wrote in The Conversation. “To demonstrate a truly global human impact requires a signal from a remote, pristine location in the Southern Hemisphere that occurs at the same time as the north. This is where our new study comes in.”
They say the tree’s peak radioactive signal, between October and December 1965, coincides with that found in the Northern Hemisphere, demonstrating “unequivocally that humans have left an impact on the planet, even in the most pristine of environments, that will be preserved in the geological record for tens of millennia and beyond.”
They also argue that the date aligns nicely with the “Great Acceleration” of global economic activity following the Second World War, when rapid industrialization drove population expansion and created a much larger human environmental impact.
Turney, a professor of Earth Science and Climate Change at the University of New South Wales, told Earther that the radioactive CO2 spike was also found in local shrubs and from a sediment core taken through a local peat bog.
“The presence of this ‘bomb peak’ in geologic-forming materials means the signal will be present for tens of millennia, allowing future geologists to identify the same signal and therefore locate the start of the Anthropocene,” he said.
The spruce—which could become world famous were it to be selected as the Anthropocene’s “golden spike”—was planted on Campbell Island in the early 20th century by then-governor of New Zealand Lord Ranfurly. It is already well known as the “world’s loneliest tree,” as there are no other trees within 170 miles. The species is found naturally along the U.S. Pacific coast. In its alien location the lone tree has never produced cones, suggesting it remains permanently in a juvenile state.
“It seems somehow apt that this extraordinary tree, planted far from its normal habitat by humans has also become a marker for the changes we have made to the planet, it is yet further evidence, if that was needed, that in this new epoch no part of our planet remains untouched by humans,” Maslin, from University College London, said in a statement.
In 2016, scientists at the International Geological Congress recommended that the 11,700-year-old geological epoch known as the Holocene be cut short and supplanted by the Anthropocene. Most geologic epochs last millions of years, but humans have greatly accelerated planetary changes. It seems it’s no longer a matter of if we’ve started a new geologic epoch, but when exactly we started it.