Are we beyond the Holocene

Anthropocene: An Epoch Debate

American Association of Petroleum Geologists (AAPG)

Today it seems like everyone’s talking about the Anthropocene, the proposed new geological Epoch of Humans.

For its 2011 annual meeting in October, for example, the Geological Society of America chose the theme “Archean to Anthropocene: The Past Is the Key to the Future.”

In England, The Geological Society held a special conference in May titled “The Anthropocene: A New Epoch of Geological Time?”

Some geologists have embraced the idea of the Anthropocene. Others remain skeptical. The final call on establishing a new epoch rests with the International Committee on Stratigraphy (ICS).

Preservation hauls: The cities of Amsterdam (above) and New Orleans one day could be wellpreserved cities – and therefore, well studied – that define the current geologic era. Photos courtesy of Moyan Brenn (top) and Rodney Herring
Preservation hauls: The cities of Amsterdam (above) and New Orleans one day could be wellpreserved cities – and therefore, well studied – that define the current geologic era. Photos courtesy of Moyan Brenn (top) and Rodney Herring

In gathering evidence for the Anthropocene, “one would look at different types of signal we have made, we are making or that we are likely to make,” said Jan Zalasiewicz, senior lecturer in geology at the University of Leicester in England.

Zalasiewicz is chair of the ICS Subcommittee on Quaternary Stratigraphy’s Working Group on the Anthropocene, and also served as a convener for the Geological Society’s conference in London.

Several types of signal in the geological record might characterize the Anthropocene, he said. For instance, people are physically altering sedimentary pathways and have substantially affected biostratigraphy.

“Humans have already changed the biology of the planet. One of the most striking things is the way we have transported species all across the world,” Zalasiewicz noted.

The worldwide spread of invasive or non-native species “will undoubtedly leave a signal in the fossil records,” he said. “It’s hard to scramble that omelet.”

And he said conversion of much of the planet’s dry land to agricultural or industrial use should also leave a marker in the record, an effect for study by future palynologists.

“You are replacing the pollen of a woodland with the pollen of a mixed agricultural landscape,” he said. “One can find even now a noticeable, palynological signal.”

Fossilized Cities

Zalasiewicz also raised the intriguing possibility of “fossilized cities” whose remains will be preserved well enough for study millions of years in the future.

Not every city will attain that status, however.

Denver and Manchester and other cities on rising land subject to inevitable erosion are out of luck and probably doomed to erasure, he said.

But for cities like Amsterdam and New Orleans, welcome to posterity.

“It’s really hard to see those not being preserved. You’d have to have a very substantial sea level drop and then erosion,” he said.

The case for a new Anthropocene epoch depends on humanity leaving behind clear evidence of planetary change, and not just any kind of evidence. It should be readily distinguished from the effects of natural occurrence.

People who see man-made climate change as a devastating global transformation support the Anthropocene idea enthusiastically, but that turns out to be not-so-good as a human signal.

Suppose that alien scientists land on this planet 50 million or 100 million years from now, and humans have long since disappeared. If the aliens begin to study the history of the Earth, what evidence of mankind’s global effect would be apparent to them?

Climate change?

Climate changes all the time, and changed long before humans appeared.

Extinctions caused by humans?

Extinctions occur throughout the geological record – and are, in fact, key to chronostratigraphy.

It’s easy to say that human beings are making catastrophic, observable, long-lasting changes to the planet.

It’s much harder to name one of those changes.

Here are a few signals that might remain for the alien scientists to ponder:

♦ Radioactive remains.

Dave Morrissey is university distinguished lecturer of chemistry at Michigan State University in East Lansing, Mich., and one of the leading experts in nuclear chemistry in the United States. He wrote the text “Modern Nuclear Chemistry” with co-authors Walter Loveland and the late Glenn Seaborg.

Morrissey acknowledged that humans have created a long-lasting signal with the radionuclides from nuclear weapons testing, and that a substantial amount of upgraded radioactive material now exists on the planet, primarily in nuclear reactors.

“The problem with nuclear power is the dispersal aspect. That material is sequestered and short lived,” he noted.

“The radioactivity from nuclear weapons sprinkled out all around the world. I think that would be pretty important from the aspect of finding it everywhere,” he said.

One possible remnant signal from nuclear power might come from people gathering up materials contaminated by radioactivity and disposing of them in one place, according to Morrissey.

If the alien scientists land so far in the future that all the isotopes have become stable, they are going to discover some bizarre isotopic ratios.

“You will find that it has a different distribution of isotopes than anything else. And that would be there for all time,” Morrissey said.

♦ Damming evidence.

Humans are manipulating the planet’s surface in all sorts of noticeable ways, from terracing slopes for agriculture to creating huge mines to trawling the seafloor, said James Syvitski.

“We fish the world’s continental shelves, and in this bottom trawling we’re plowing the seafloor. And that would show up in the geological record,” he said.

Syvitski is a professor at the University of Colorado at Boulder and director of the university’s Community Surface Dynamics Modeling System facility. His work on contemporary sediment flux speaks directly to the Anthropocene concept, notably regarding rivers and sediment transport.

“We certainly have stirred the landscape, and the rivers carried the sediment. In some cases that created deltas where there were never deltas before,” Syvitski said.

Activities like deforestation and agriculture and mining filled the rivers with sediment, which emptied into gulfs and oceans. Then about 1950 that signal reversed, he said.

For an idea of what happened, China before 1950 had eight dams, as Syvitski noted in a paper on sediment flux. By the 1980s, China had more than 13,000 dams.

Not only do dams control flow and create sediment-trapping reservoirs, they also alter river movement.

“Rivers migrate, and because of this migration they would form a fairly good, fairly thick sediment layer. But now we don’t allow rivers to move,” he said.

Syvitski predicted the dominant signal in the future will be more and more dams. And that pattern occurs all over the world.

“It’s actually shocking,” he said. “We had a project going to find pristine rivers for study, and we had a heck of a time finding pristine rivers on Earth.”

♦ Ecological change.

Humans began changing the surface of the planet long before the past century, said Erle Ellis, associate professor of geography and environmental systems at the University of Maryland, Baltimore County, in Baltimore.

“I came at this looking at long-term ecological change,” Ellis said. “That gave me the perspective that people have been around and have been changing the Earth for a long time.”

His academic work includes studying the long-term changes in landscape structure and biogeochemistry across China’s densely populated agricultural areas.

“There have been unambiguous signals,” Ellis noted. “Rice paddy soil is completely different from the natural soil horizon after they’ve been farmed for hundreds of years.”

Also, “there’s no good explanation for domesticated species, other than other species domesticating them,” he said.

As humans spread across the planet, they transplanted species far from native habitats. The resulting mixture would seem to be a sure signal of the Anthropocene, Ellis noted.

“There are more species that are in one place today than there have ever been before. If you are looking at one rock, you would see evidence of more species than you’ve ever seen before,” he said.

He thinks those kinds of changes already are enough to prove a global, human effect.

“It’s profound,” he said. “It’s long term. If we stopped affecting the biosphere today, there would be obvious signs of it.”

♦ Signal strength.

One problem for supporters of an Anthropocene epoch is the strength of the unique signals humans are leaving on the planet, especially seen from a perspective of 50 million years in the future. The Earth is a big place, and not that easy to change.

“When you start thinking about things the way a stratigrapher has to think, it gets much tougher to think what the signals might be,” Ellis observed.

“There are a lot of things, looking back, that are going to be hard to see,” he said.

But there’s still hope for a strongly demarcated Anthropocene.

If humanity manages to destroy itself in an all-out nuclear war, that should leave a nice, clear signal in the record.

And in the end, the best evidence for human life on Earth could be – human life on Earth.

An alien scientist looking back at humans in this period might think, “Good gosh. There were billions of these things. And they were everywhere!”

Because the Holocene epoch began about 11,700 years ago and the human population began its mastery of agriculture and modern expansion more than 9,000 years ago, the two roughly overlap. The smart money might be on a Holocene-Anthropocene.

“A more conservative approach would be to call the Anthropocene a subdivision of the Holocene. That would certainly be less controversial,” Zalasiewicz noted.

With scientists from many disciplines working to develop supporting evidence, a formal proposal for an Anthropocene epoch might be ready in time for the 35th International Geological Congress in South Africa in 2016, he said.

Until the issue is settled, debate over the Anthropocene continues.

“I can’t predict what the outcome will be,” Zalasiewicz said, then added:

“I suspect the term will not go away. In a remarkably short time, it has become embedded in people’s minds and in the literature.”

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