Scientists Start the Clock on Human Impact

The Earth at night from space. (Photo: NASA).

Though it's clear we're currently living in it, scientists have long debated when the Anthropocene, the epoch of human dominance over the planet, first began.

The Anthropocene Era refers to the period of time humans have had a measurable global impact on Earth's ecosystems.

Did it start with the advent of agriculture around 10,000 years ago? With the Industrial Revolution? With the first explosions of nuclear weapons in the 1940s?

The Anthropocene Working Group (AWG), a panel of scientists, recently voted to official recognize the epoch and suggested starting it in the middle of the 20th century, according to Nature.

They are now working to determine a "golden spike," or a feature that best describes its start. It may be hydrogen bomb tests in the 1950s, for example, or the increase of industrial production and the widespread use of agricultural chemicals.

“The Anthropocene works as a geological unit of time, process and strata,” says Jan Zalasiewicz, chair of the AWG and a geologist at the University of Leicester, U.K.. Zalasiewicz wasn’t sure of that conclusion when the AWG began its work a decade ago. But the current vote shows that the group has mostly reached agreement on the idea of the geological unit. “It is distinguishable. It is distinctive,” he says.

Earlier ideas suggest an earlier start

At one point, 2015 data suggested the Anthropocene Era may have actually started in the year 1610.

What happened in 1610 that made it such a tipping point for humanity's impact on Earth? According to Simon Lewis, an ecologist at University College London, and geologist Mark Maslin of Leeds University, a golden spike can be seen in the global geological record in this year which can be directly attributed to humans, reports the Independent.

Two global signatures appear in 1610: Pollen from imported New World crops begins to appear in Europe, and a massive dip in carbon dioxide levels can be seen in Antarctic ice cores dating to that time. Both of these events are a direct result of increased trade and transport of animals and plants across the Atlantic Ocean — a barrier that had previously kept the New and Old Worlds separated for millions of years.

In the case of the global dip in carbon dioxide, Lewis and Maslin believe this to be the result of the deaths of millions of indigenous people in the aftermath of European colonization. As many as 50 million Native Americans died in the aftermath of European expansion into the New World, mostly as a result of infectious diseases such as smallpox. As their numbers dwindled, the resultant loss in agriculture allowed forests to re-grow throughout the Americas. These expanded forests scrubbed the atmosphere of carbon dioxide.

"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," said Lewis. "They will be in no doubt that these global changes to Earth were caused by their own species. The anthropocene probably began when species jumped continents, starting when the old world met the new."

Lewis and Maslin contend that this is the first time that human actions had a truly global impact. The bridging of the Old and New Worlds fundamentally changed the entire biosphere of the planet. This was not just a regional impact; its ecological footprint stretched around the world.

"We humans are now a geological power in our own right, as earth-changing as a meteorite strike. Historically, the collision of the old and new worlds marks the beginning of the modern world," Lewis added.