London: The human-dominated geological epoch known as the Anthropocene probably began around the year 1610, with an unusual drop in atmospheric carbon dioxide, scientists say.
Previous epochs began and ended due to factors including meteorite strikes, sustained volcanic eruptions and the shifting of the continents.
Scientists at University College London have concluded that humans have become a geological power and suggest that human actions have produced a new geological epoch.
Defining an epoch requires two main criteria to be met. Long-lasting changes to the Earth must be documented. Scientists must also pinpoint and date a global environmental change that has been captured in natural material, such as rocks, ancient ice or sediment from the ocean floor.
Such a marker - like the chemical signature left by the meteorite strike that wiped out the dinosaurs - is called a golden spike.
The study authors systematically compared the major environmental impacts of human activity over the past 50,000 years against these two formal requirements.
Just two dates met the criteria: 1610, when the collision of the New and Old Worlds a century earlier was first felt globally; and 1964, associated with the fallout from nuclear weapons tests. The researchers concluded that 1610 is the stronger candidate.
The scientists said the 1492 arrival of Europeans in the Americas, and subsequent global trade, moved species to new continents and oceans, resulting in a global re-ordering of life on Earth.
They argued 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 fossil pollen of maize, a Latin American species, appears in marine sediment in Europe in 1600, becoming common over subsequent centuries.
This irreversible exchange of species satisfies the first criteria for dating an epoch long-term changes to Earth.
The researchers found a golden spike that can be dated to the same time: a pronounced dip in atmospheric carbon dioxide centred on 1610 and captured in Antarctic ice-core records.
The drop occurred as a direct result of the arrival of Europeans in the Americas. Colonisation of the New World led to the deaths of about 50 million indigenous people, most within a few decades of the 16th century due to smallpox.
The abrupt near-cessation of farming across the continent and the subsequent re-growth of Latin American forests and other vegetation removed enough carbon dioxide from the atmosphere to produce a drop in CO2.
Thus, the second requirement of a golden spike marker is met, researchers said.
"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," said lead author, Dr Simon Lewis from UCL Geography and University of Leeds.
