The older you get, the faster the time goes.
Our 4.57-billion-year-old planet may know the feeling. After all, some scientists are suggesting Earth has already entered a new age—several million years earlier than it should have.
Earth's geologic epochs—time periods defined by evidence in rock layers—typically last more than three million years.
We're barely 11,500 years into the current epoch, the Holocene. But a new paper argues that we've already entered a new one—the Anthropocene, or "new man," epoch.
The name isn't brand-new. Nobel Prize-winner Paul Crutzen, a co-author of the paper, coined it in 2002 to reflect the unprecedented changes humans have wrought in the roughly 200 years since the industrial revolution.
The report, however, is part of new push to formalize the Anthropocene epoch.
Recent human impacts—including habitat destruction, environmental pollution, and animal and plant extinctions—have been so great that they'll result in an obvious boundary in Earth's rock layers, the authors say.
(Find out how degraded soil might be evidence that we've entered the Anthropocene epoch.)
"We are so adept at using energy and manipulating the environment that we are now a defining force in the geological process on the surface of the Earth," said co-author Jan Zalasiewicz, a paleobiologist with the University of Leicester in the U.K.
Even so, it could take years or even decades for the International Union of Geological Sciences, the world's geological governing body, to formalize the new epoch.
Hard Evidence Needed
If the concept of the Anthropocene epoch is to be formalized, scientists will first have to identify and define a boundary line, or marker, that's literally set in stone.
"The key thing is thinking about how—thousands or hundreds of thousands of years in the future—geologists might come back and actually recognize in the sediment record the beginning of the Anthropocene," explained paleoclimatologist Alan Haywood of the University of Leeds in the U.K.
"It's not as straightforward as you might think, because the marker has to be very precise, and it has to be recognized in many different parts of the world," said Haywood, who wasn't involved in the new study.
One candidate for the marker is the distinctive radioactive signature left by atom bomb tests, which began in 1945. "The fallout is basically across the world," Haywood said.
In a similar way, scientists use traces of the element iridium left by meteor strikes to help define the boundary between the Cretaceous and Tertiary periods—about 65.5 million years ago, the time of the great dinosaur extinctions (prehistoric time line).
Today's life-forms, once fossilized, could also serve as future markers of the proposed Holocene-Anthropocene boundary, co-author Zalasiewicz told National Geographic News.
For instance, studies suggest that marine plankton now have a different carbon isotope signature than they did before humans began burning fossil fuels on a wide scale, Zalasiewicz said.
Likewise, permanent traces of pollution—such as lead particles released when leaded gasoline is burned—might help define the epoch.
The push for a formal declaration of the Anthropocene epoch is about more than just scientific curiosity.
The move, the scientists write in the latest issue of the journal Environmental Science & Technology, "might be used as encouragement to slow carbon emissions and biodiversity loss" or "as evidence in legislation on conservation measures."
The University of Leeds's Haywood said that, by underscoring how much we're changing the environment, the formalization would be "a very powerful statement."
But while "there are good scientific justifications for saying we have moved into the Anthropocene," he said, "we mustn't base that on a politically expedient decision."
Co-author Zalasiewicz also ruled out politics as a deciding factor.
"Changes to the geological time scale are treated with great seriousness by scientists," Zalasiewicz added, "particularly here, where we're dealing with a time interval which is only just starting."
Living in the Past?
Some scientists argue we haven't even entered the Holocene epoch—never mind the Anthropocene.
The Holocene, they say, isn't an epoch at all—just another warm period within the Pleistocene, which began about 2.6 million years ago.
"The period we're living in is the Ice Age, basically," said geologist Philip Gibbard of the University of Cambridge in the U.K. "There is no reason to think it has finished," if history is any guide.
Assuming human-made global warming doesn't change the climate on a geologic time scale, the Ice Age should go on for at least another million years, with continuing oscillations between warm and cold periods, Gibbard said.
"We would expect the oscillations [between warm and cold ages] which we have seen in the near past to continue for at least a period of one million years."
(See "Next Ice Age Delayed by Global Warming, Study Says.")
If scientists really want a time period defined by the presence of humans, he said, they've already got one—the Holocene, whose start date, he says, is based more on the dawn of civilization than on changes in the geological record.
"That means the Anthropocene concept is a little bit like adding sugar to the tea," Gibbard said.
(Related: "Sun Oddly Quiet—Hints at Next 'Little Ice Age'?")
Epoch Not Built in Day
Whatever the final decision on the Anthropocene, it won't be a hasty one, said co-author Zalasiewicz. "The Geological Time Scale is held dear by geologists [because it is fundamental to their work]," he and his co-authors write, "and it is not amended lightly."
An expert panel called the Anthropocene Working Group has already been formed within the International Union of Geological Sciences to consider the matter. But the committee will probably take three to five years to reach a verdict, Zalasiewicz said.
Any decision would then have to pass a series of review committees before going to the wider union for ratification.
Zalasiewicz said there might be more urgency to formalize the Anthropocene these days, given that the term "is out there, is being used by working scientists, and is being used in the scientific literature."
But, he said, formalization probably won't occur for at least ten years.