The Human Epoch: What We'll Leave Behind

In 1 million years, the epoch that we are now living in will likely be characterized by animal and plant remains, along with a strange mess of industrial pollutants.

We are in a new geological epoch that is marked by the impact of human activity on Earth. The evidence is now overwhelming that the time we are living in, known as the Anthropocene, should be officially recognized as an epoch that is distinct from the Holocene, according to new research in the journal Science.

The Holocene started 11,700 years ago at the end of the last ice age. Lead author Colin Waters of the British Geological Survey told Discovery News that the Holocene "was very much a natural phenomenon, representing part of the cyclical variation in the orientation of the Earth's orbit around the sun."

He says our species, which has been around for about 200,000 years, initiated many developments then that characterize our modern civilization, such as living in settlements, deforestation, agriculture and domestication of livestock.

Starting at around 1950, however, our influence became truly global, Waters said, "modifying not just the geosphere, but the atmosphere, hydrosphere, and cryosphere often in a linked effect, and at the same time the changes are incredibly rapid -- annual to decadal."

The researchers also believe that the present Anthropocene, aka the "Human Epoch," will leave behind its own unique geological signature far into the future. This assumes that the planet will not be blown to smithereens by bombs, a meteor or some other disaster. Part of that signature would consist of our skeletal remains.

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Aluminum is the second most abundant metallic element in the Earth's crust after silicon, but it is a comparatively new industrial metal that is associated with the Anthropocene.

"It will likely oxidize with time to aluminum oxide, but should be preserved as a trace of the original artifact," Waters said. So future generations might associate our epoch with the use and manufacture of aluminum products.

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Concrete is another frequently used material that will likely be associated with our epoch in future, Waters and his team say. Roman concrete, for example, has proven to be incredibly durable, surviving intact for at least 2,000 years.

"Over a much longer duration, if the concrete were (deeply) buried it could interact with ground waters to produce highly alkaline fluids that could migrate away from the source and re-cement elsewhere as calcium carbonate," Waters said.

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Both black carbon and fuel ash are likely to provide a persistent signature tied to the Human Epoch, the scientists believe. This evidence of our time is expected to last for millions of years.

Waters explained, "Organic carbon is a stable component of natural marine sediments of hundreds of millions of years in age. Carbon spherules, similar in nature to the fuel ash from thermal power stations, have been found from the 65-million-year-old meteorite impact, suggesting a degree of long-term persistence."

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Nitrates, primarily from fertilizers, will also probably persist in the geological record associated with humans from the 1950s onward. As for why the mid 20th Century point is so important, the researchers explained that accelerated human population growth, industrialization, technological advances, mineral and energy use, and globalization of the economy all then began to heavily impact ecosystems and the environment.

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Excessive amounts of carbon dioxide will also be associated with the Human Epoch, assuming that the Anthropocene is determined to be an actual epoch. Waters and his team are members of the Anthropocene Working Group, charged with the stratigraphic definition of this time.

The final decision about the naming would have to come from the group's parent body, the Subcommission on Quaternary Stratigraphy. Whatever their decision is, evidence of our carbon dioxide releases will persist for a very long time.

Carbon dioxide is a greenhouse gas whose concentration has rapidly increased in the atmosphere during recent decades, due to the burning of carbon-based fuels and other materials. Waters said that naturally occurring carbon dioxide has left behind geological evidence dating to at least 350 million years ago, so the high levels tied to our proposed epoch could be detected well into the future.

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Methane is the second most prevalent greenhouse gas, behind only carbon dioxide as a gas that can dangerously trap and hold heat in the atmosphere. It is emitted by natural sources -- such as wetlands, natural gas systems and animal flatulence.

Globally, over 60 percent of total methane emissions come from human activities, according to the EPA, including industry, agriculture and waste management. Similar to carbon dioxide, evidence for excessive methane associated with the proposed Human Epoch is expected to last for many years to come.

The good news is that methane emissions, along with release of black carbon and fuel ash, seem to have already reached their peaks. Particulate amounts of the latter two, for example, "peaked between about 1970 and 1990," Waters said, adding that decommissioning of big thermal power stations is expected to further decrease levels of these pollutants.

"In most cases," he said, "if we turned our global attention to changing factors, such as with greenhouse gases, it is within our capabilities to turn around those signals."

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Plastics are a product of our era. Waters said that even if plastic items decay to hydrocarbons in the distant future, they will still leave behind a persistent geochemical signature "and also a trace of the original item."

He explained, "The void, by say a decomposed plastic bottle top, might be filled with sediment and preserved as a trace fossil maintaining at least the shape of the item to confuse future geologists."

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Remains of plants and animals from our time will also last well into the future, forming still another part of the Human Epoch's lasting, tangible legacy.

"These (remains) could be used the way we have used such fossils throughout the last 500 million years of geological history to correlate rocks," Waters said. "These provide very long-lasting signatures."

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Perhaps the worst lasting evidence from our time will be radionuclides, which are unstable atoms. Large amounts of them, for example, disperse into the atmosphere whenever certain nuclear weapons are tested.

Waters said plutonium has a half-life of 24,110 years, and will be detectable by modern mass spectrographic techniques for about 100,000 years. After then, it will still leave behind telltale signs of its former presence. From radionuclides to plastics, it is already a given that our era in future will be represented, at least in part, by pollution-causing industrial materials.

On a more positive note, Waters said we have "created a planet that sustains 7 billion people living longer durations than at any point in history."

That should be recognized by future generations, too. Epochs come and go, however. No one can yet predict how and when the Anthropocene will end, yet one sobering possibility is nearly a given.

"Ultimately, processes that greatly reduce the human population are most likely to bring the Anthropocene to a close," Waters said.

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