While 1492 may have been the year Columbus sailed the ocean blue, it also marks the start of a mass swapping of species between the Old World and the New World as Europe began colonizing the Americas.
Research published Wednesday from University College of London (UCL) and Leeds University Professor Simon Lewis and UCL Professor Mark Maslin argues that just over 100 years later -- 1610 -- is when those actions dramatically changed the planet Earth.
As a result, they say, 1610 deserves to be designated as the start of the Anthropocene Epoch.
The Anthropocene is known as the "human epoch," and scientists have debated its exact starting point for some time. For a new epoch to begin, Lewis and Maslin assert, two conditions must be satisfied. "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," according to a statement about their research.
The researchers picked 1610 because they believe it best satisfies these two criteria.
Satisfying the first condition is the fact that the wide-scale swapping of species between continents that began in 1492 was first truly felt in 1610. "This rapid, repeated, cross-ocean exchange of species is without precedent in Earth's history," according to the researchers.
For the second "golden spike" condition to be satisfied, the researchers turned to core samples of Antarctic ice, which showed a dramatic dip in atmospheric carbon dioxide levels in 1610. They theorize that this was caused by the rampant death that followed the colonizers in the New World as an estimated 50 million people were exterminated, largely by smallpox. Because many of those people were farmers -- especially in Latin America -- when their fields were no longer tended, trees were able to grow back and suck carbon dioxide out of the atmosphere.
"The growth of all those trees had sucked enough carbon dioxide out of the sky to cause a drop of at least seven parts per million in atmospheric concentrations of the most prominent greenhouse gas and start a little ice age," says a report in Scientific American.
The researchers decided to name the carbon dioxide dip the "Orbis Spike," using the Latin word for "world," because it marks the first time planet inhabitants intermingled so dramatically.
An official decision about the Anthropocene Epoch and the proposal to set it at 1610 is expected from the Anthropocene Working Group of the Subcommission of Quaternary Stratigraphy in 2016. These things do, after all, take time.
"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," Lewis said in a statement about the research, which was published in the journal Nature.
"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."