King James was on the throne, Shakespeare’s Cymbeline was playing in the theatre and Galileo discovered four moons of Jupiter. In future, though, 1610 could be chiefly remembered as the geological time-point at which humans came to dominate Earth.
Scientists have argued that it is time to draw a line under the current geological epoch and usher in the start of a new one, defined by mankind’s impact on the planet.
The year 1610 is a contender for marking the transition, they claim, because this is when the irreversible transfer of crops and species between the new and old worlds was starting to be acutely felt.
Simon Lewis, an ecologist at University College London and author of the paper, said: “In a hundred thousand years, scientists will look at the environmental record and know something remarkable happened in the second half of the second millennium. They will be in no doubt that these global changes to Earth were caused by their own species.”
When Europeans started arriving in the Americas, he added, a cascade of events was triggered that was “as Earth-changing as a meteorite strike”.
The concept of the “anthropocene” is already widely used on an informal basis by writers and environmentalists, but scientists remain divided on whether the designation of a new time period is justified.
Critics argue that the desire to redraw geological boundaries is politically motivated by those wanting to highlight the extent of human destruction on the planet. Others say that it is about 1,000 years too soon to identify the most enduring geological markers of human activity on Earth.
The International Commission on Stratigraphy (ICS), the world body that decides on geological time boundaries, is actively considering the question and a working group is due to report on the issue next year.
The central problem is identifying a permanent and global change that has been captured in natural material, such as rocks, ice or marine sediment – a so-called “golden spike”.
“Global long-term changes to Earth’s system … are required to have one marker that can be precisely dated that is captured in some ancient geological material,” said Lewis.
Lewis and his UCL co-author, Mark Maslin, considered and rejected the earliest use of fire, the dawn of agriculture and the industrial revolution as possible candidates.
Eventually they identified two events – the joining of the two hemispheres and nuclear testing in the 20th century – that met the golden spike criteria.
The year 1610 marks the low-point of a dip in global carbon dioxide levels caused by a drastic reduction in farming in the Americas. This was a knock-on effect of the 50 million or so indigenous deaths that resulted from the introduction of small pox to the continent by European colonialists. A secondary marker of the colliding of worlds is the sudden appearance, in 1600, of fossil pollen maize, a Latin American species, in the European marine record.
The paper, published today in Nature, also considered the year 1964, which saw a peak in radioactive fallout following nuclear weapons testing before the test ban treaty came into force.
The authors conclude that 1610 has a stronger claim because so far the testing of nuclear weapons has not been an Earth-changing event. “I tend to go with 1610 because … the evolutionary consequences of that are pushing Earth onto a new evolutionary trajectory,” said Lewis.
Jan Zalasiewicz, chair of the ICS’s Anthropocene working group, said his committee would consider the authors arguments. However, the working group is converging on nuclear testing as a more universal marker - the CO2 dip and pollen records are patchy and have fuzzier boundaries, he contends.
A potential downside of the nuclear signal is that it will have decayed away within 100,000 years – a blink of the eye in geological time. “Geologists are very pragmatic creatures though,” said Zalasiewicz. “We’re looking for the best signal for dividing strata now, not for geologists a million years in the future.”
The arrival of the Anthropocene would mark the end of the Holocene, the epoch that we currently live in, which itself was only defined in 2008. It is marked by a signal in the Greenland ice cores indicating the end of the last ice age, 11,700 years ago.
Since epochs typically last tens of millions of years, some suggest that the Holocene should not only end, but be scrapped or downgraded. “The Holocene is supposed to last tens of millions of years and it’s several orders of magnitude to short,” said Lewis. “I think we’d have to call that a stage rather than an epoch.”
