Scientists have been wondering how to define ‘Anthropocene’, the current geological age when human activity became a dominant influence on Earth’s climate and environment, and have proposed 1610 as a starting date.
The authors, who published their findings in the academic journal Nature Perspectives (citation below), say 1610 was when there was an unusual decline in atmospheric carbon dioxide and the irreversible exchange of species between the New and Old Worlds.
In other words, human activity caused long-term changes to Earth that started in 1610 and will last hundreds of thousands of years, just like the huge meteorite that struck the Yucatan peninsula and led to the extinction of the dinosaur and several other species.
The Columbian Exchange refers to the widespread transfer of animals, plants, culture, human populations, communicable diseases, technology and ideas between the New and Old Worlds in the 15th and 16th centuries.
Previous epochs started and finished as a result of natural factors, such as sustained volcanic eruptions, meteorite/asteroid impacts, and the shifting of continents. Our planet is now changing because of human actions. But are we really a geological force of nature that will drive Earth into a new epoch lasting a geologically relevant period, i.e. millions of years?
Humankind has sparked a new epoch
Scientists at University College London (UCL) believe we have become a geological force and suggest that human activity has produced a new geological epoch.
An epoch requires two main criteria:
1. There needs to be documentation of long-lasting changes to Earth.
2. Scientists need to be able to pinpoint and date a worldwide environmental change that has been captured in natural material, such as the sediment from the ocean floor, ancient ice, or rocks.
An example of such a marker, like the meteorite strike that drove dinosaurs to extinction, is called a Golden Spike.
The authors systematically examined and compared the major environmental impacts of human activity of the last 50,000 years against those two main criteria.
Collision of Old & New Worlds or Nuclear Testing Fallout?
They came up with a shortlist of two dates: 1610, when the collision of the Old and New Worlds one hundred years earlier was first felt globally; and 1964, associated with the nuclear weapons tests and their fallout. There is geological evidence of both in rocks and marine sediment.
The scientists felt that 1610 was the stronger candidate.
In 1492 Christopher Columbus arrived in the Americas. The subsequent global trade moved species across new continents and oceans, which led to a global re-ordering of life on our planet. This rapid, repeated transatlantic exchange of species had never happened before in the history of our planet.
The authors, Dr. Simon Lewis (UCL Geography and the University of Leeds) and Professor Mark Maslin (UCL Geography), argue that the joining of the two hemispheres is an “unambiguous event after which the impacts of human activity became global and set Earth on a new trajectory.”
The first fossilized maize pollen, a species that comes from Latin America, appears in marine sediment in Europe in 1600, becoming more common over the centuries that followed. “This irreversible exchange of species satisfies the first criteria for dating an epoch – long-term changes to Earth,” they wrote.
About 50 million Amerindians died in the first few decades of the 1600s, mainly from smallpox, an Old World disease.
The ‘Golden Spike’
The scientists also found a Golden Spike that can be dated around 1610 – a significant decline in atmospheric CO2 captured in Antarctic ice-core records.
The drop in CO2 levels was a direct result of the arrival of Europeans in the New World. The colonization of the Americas led to the deaths of 50 million indigenous people. Most of them died during the first few decades of the 16th century from smallpox.
This led to an abrupt, almost total cessation of farming across the continent, and the subsequent re-growth of Latin American forests and other vegetation which removed atmospheric CO2. Thus, the second Golden Spike requirement is met.
The authors have dubbed the 1610 dip in CO2 the ‘Orbis Spike’. Orbis is Latin for ‘World’. This Golden Spike was caused by once-disconnected peoples who became globally linked.
“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.”
“Today we can say when those changes began and why. The Anthropocene probably began when species jumped continents, starting when the Old World met the New. We humans are now a geological power in our own right – as Earth-changing as a meteorite strike.”
Dr. Lewis added:
“Historically, the collision of the Old and New Worlds marks the beginning of the modern world. Many historians regard agricultural imports into Europe from the vast new lands of the Americas, alongside the availability of coal, as the two essential precursors of the Industrial Revolution, which in turn unleashed further waves of global environmental changes.”
“Geologically, this boundary also marks Earth’s last globally synchronous cool moment before the onset of the long-term global warmth of the Anthropocene.”
With no nuclear war, 1960s is a weak candidate
Dr. Lewis and Prof. Maslin also considered the merits of dating the Anthropocene to 1964, when the radioactive fallout following nuclear weapons testing peaked. Scientists can see this marked in several geological deposits. The human impact on the Earth was large by the 1960s.
However, the authors pointed out that while a nuclear war would alter the Earth dramatically, so far we have not had one.
“While the fallout from nuclear bomb tests is a very good marker, the testing of nuclear weapons has not been – in geological terms – an Earth-changing event,” they explained.
Industrial Revolution lacks a ‘Golden Spike’
Some archaeologists, geologists, historians and anthropologists have suggested the Industrial Revolution in the late 18th century as the starting date of the Anthropocene. This period marked a clear turning point in the history of humankind, and the increase in atmospheric CO2 from fossil fuel usage will have a long-term impact on the environment of our planet.
However, the Industrial Revolution has no Golden Spike, the authors say. Most of the effects were local at that time, while the global exponential rise in carbon dioxide was too gradual to form a precisely dated marker.
Prof. Maslin said:
“A more wide-spread recognition that human actions are driving far-reaching changes to the life-supporting infrastructure of Earth will have implications for our philosophical, social, economic and political views of our environment.”
“But we should not despair, because the power that humans wield is unlike any other force of nature, it is reflexive and therefore can be used, withdrawn or modified. The first stage of solving our damaging relationship with our environment is recognising it.”
The official decision on whether the Anthropocene should be recognized, and if so when it began, will be initiated by a recommendation of the Anthropocene Working Group of the Subcommission of Quaternary Stratigraphy, due next year.
Citation: “Defining the Anthropocene,” Simon L. Lewis & Mark A. Maslin. Nature Perspectives. Published 12 March, 2015. DOI: 10.1038/nature14258.