On a cosmological timescale, humanity鈥檚 existence is a mere blip. Yet, in our short lifetime, we have done outsized damage to Earth, so much so that some believe we need to invent a new geological epoch, the Anthropocene, to recognise the global change our species has caused. Technically speaking, we aren鈥檛 yet in the Anthropocene 鈥� but that is largely because experts can鈥檛 agree about when it started.
Ask most geologists and they will say we are still in the Holocene, a geological epoch that began about 11,700 years ago and is characterised by a period of planetary stability when human civilisation flourished. But therein lies the rub: our influence on Earth systems means these characteristics no longer apply, and a growing number of scientists believe a new epoch must be recognised. Enter the Anthropocene.
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There is debate about who coined the term, but it was popularised in 2000 by atmospheric chemist and Nobel laureate and biologist Eugene Stoermer. They argued that the Anthropocene began in the 鈥渓atter part of the eighteenth century鈥�, around the time that global greenhouse gas emissions began to rise as the industrial revolution gathered steam. However, the Anthropocene Working Group (AWG) begged to differ. Established in 2009 and tasked with coming up with a formal definition of the epoch, its members said that the effects of human activity at that time were too scattered to provide a picture of global change. Instead, the date they came up with was 1952.
鈥淭he mid-20th century worked much better than any of the other candidates,鈥� says at the University of Leicester, UK, who chaired the AWG. Starting in 1952, radioactive fallout from hydrogen bomb tests resulted in a worldwide uptick in plutonium in rock strata. Pollution from microplastics, fossil fuels, pesticides and forever chemicals , sediments and coral skeletons. There is evidence of changes in atmospheric and oceanic circulation too. Earth shows 鈥渉undreds of signals鈥� of human influence globally, says Zalasiewicz. 鈥淚t is a transformation.鈥�
How humans are transforming Earth
However, for some, a 1952 start date for the Anthropocene is too close for comfort. 鈥淔rom the beginning, a number of my geological colleagues were deeply unhappy with the idea of a geological epoch that could be as short as 70 years,鈥� says Zalasiewicz. They aren鈥檛 alone: some ecologists and social scientists believe that any definition of the Anthropocene must account for the broad sweep of human history. 鈥淭here is not a precise date for the beginning of the Anthropocene, in my view,鈥� says geographer at University College London. 鈥淩ather, it points to the accumulation of transformations over a very long period of time, which have become increasingly critical over the last 50 years or so.鈥�
Zalasiewicz believes we need a precise date to recognise the scale of change humanity has wrought on Earth. He fears that the lack of one creates uncertainty in the minds of the public. 鈥淭he main point about formalisation isn鈥檛 simply to have the Anthropocene there on a geological timescale,鈥� he says. 鈥淚t鈥檚 a means of stabilising the idea鈥� so that it鈥檚 widely known and isn鈥檛 confused.鈥� Nevertheless, last year, when a proposal to define the Anthropocene as beginning in 1952 came to a formal vote, senior geologists rejected it by 12 votes to four.
Geologists won鈥檛 get another chance to consider when the Anthropocene began for at least a decade. So, for now, it is in limbo: not yet a formal geological epoch, but, depending on who you ask, already well under way.
This article is part of a special series exploring seven of the biggest chronological conundrums of all time.
The science of deep time: Wales
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