When humansfirst set foot on the moon in 1969, the people of that decade thought the worldhad changed forever. Little did they know the world had already laid down theprecise marker of a far greater global change four years earlier, signalling ourplanet had entered an entirely new geological epoch, the Anthropocene.
That newepoch began between October and December 1965 according to new researchpublished today in Scientific Reportsby members of the Australasian Antarctic Expedition 2013-2014.
Theresearchers were able to mark this profound change so precisely because of a radiocarbon"golden spike" found in the heartwood of a strange and singular tree, a SitkaSpruce found on Campbell Island, a World Heritage site in the middle of theSouthern Ocean. The spruce is locally referred to as ‘the loneliest tree in theworld’ with the next closest tree over 200km away on the Auckland Islands.
The radioactivecarbon spike was created by the culmination of mostly Northern Hemisphereatmospheric thermonuclear bomb tests in the 1950s and 1960s. The signal was fixedin the wood of the Campbell Island Sitka spruce by photosynthesis.
"We wereincredibly excited to find this signal in the Southern Hemisphere on a remote island,because for the first time it gave us a well-defined global signature for a newgeological epoch that could be preserved in the geological record," said leadauthor Prof Chris Turney (University of New South Wales).
"Thousandsof years from now this golden spike should still stand as a detectable markerfor the transformation of the Earth by humankind."
Various researchersfrom around the world have been talking about declaring a new geological epochcalled the Anthropocene, indicating the point where human influence on theplanet fundamentally changed the natural world. However, for a new epoch to be officiallydeclared there must be a clear and precise "global" signal that can be detectedin the geological forming materials of the future. This radiocarbon spike isthat signal.
In the NorthernHemisphere, the atmospheric radiocarbon peak occurred in 1964 where the signal ispreserved in European trees. That same peak took until late 1965 to reach the SouthernHemisphere atmosphere. With that spruce, the signal became global, precise anddetectable in the geological record, meaning it fitted the requirements as amarker for a new epoch.
The 100-year-oldtree itself is an anomaly in the Southern Ocean. It is naturally found alongthe North American Pacific Coast but it is credited with being planted onCampbell Island by the Governor of New Zealand in 1901. The oceanic climate hashad an unusual effect on the spruce. Although it has grown to 10m tall, thetree has never produced cones, suggesting it has remained in a permanentlyjuvenile state.
"It seems somehowapt that this extraordinary tree, planted far from its normal habitat by humanshas also become a marker for the changes we have made to the planet," said co-authorProfessor Mark Maslin (University College London).
"It is yetfurther evidence, if that was needed, that in this new epoch no part of ourplanet remains untouched by humans."
The research is supported by the Australasian Antarctic Expedition2013-14, the Australian Research Council, the New Zealand Department ofConservation and the University New South Wales. Funding support was alsoprovided by the Crown Research Institutes from the New Zealand Ministry ofBusiness, Innovation and Employment’s Science and Innovation Group.
Prof Chris Turney is AustralianResearch Council (ARC) Laureate Fellow, Co-Director of the PANGEA ResearchCentre (UNSW), and Node Director of the ARC Centre of Excellence for AustralianBiodiversity and Heritage (CABAH).
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