For years, the term "Anthropocene" has been used to informally describe the human era on Earth. But new evidence suggests there's nothing informal about it. We're a true force of nature -- and there's good reason to believe we've sparked a new and unprecedented geological epoch.
A team of international geoscientists say the time has come for us to formally recognise the Anthropocene as a new epoch, one as significant as previous geological eras like the Holocene and Pleistocene. According to the new study, which appears in the latest issue of Science, it began sometime around the midpoint of the 20th century, and is fuelled by a number of unquestionably human influences -- including elevated greenhouse gas levels and the global proliferation of invasive species, along with the spread of materials such as aluminium, concrete, fly ash and even fallout from nuclear testing.
In geology, stratum describes a layer of sedimentary rock, soil, or ice with consistent characteristics that distinguish it from other layers. By studying strata, scientists can track changes to the Earth over time. (Image credit: Strata in Salta, Argentina, Flickr)
The study was co-authored by 24 members of the Anthropocene Working Group, including Jan Zalasiewicz and Colin Waters from the British Geological Survey. These scientists are studying the extent to which our actions can be recorded as measurable signatures in geological strata -- layers of sedimentary rock, soil, or ice with consistent characteristics to distinguish between them -- and how our activities and byproducts are driving Earth into an entirely new geological epoch.
"Our evidence suggests that the kind of earth system changes, and their stratigraphical products, that humans have generated are comparable with those of the geological past," Zalasiewicz told Gizmodo. "There is significant geological reality underlying the Anthropocene concept, on a scale that is consistent with potential formalization."
Zalasiewicz says it's important to characterise the Anthropocene more precisely, and to make it more useful in wider communication. What's more, it shows that "our species is clearly capable of altering the course of Earth history rather more than the average species".
(Credit: C. N. Waters et al., 2015/Science)
New evidence presented by the researchers shows that our current world is markedly different than the stable Holocene Epoch of the previous 11,700 years. The Holocene began at the end of the last ice age, but unlike other epochs, it features a highly intelligent and resourceful species that's been dramatically influencing the environment.
Early efforts to define and circumscribe the Anthropocene cite the advent of agriculture, animal domestication, deforestation, and tiny -- but measurable -- increases in atmospheric carbon dioxide and methane levels. Other major developments include the colonisation of the Americas and the subsequent exchange of New and Old world species, and the beginning of the Industrial Revolution.
Pulp and Paper Mill (Credit: Akexvye/CC BY 3.0)
But none of these activities, say the Anthropocene Working Group, has done as much to change the very fabric of the planet itself as the so-called "Great Acceleration" -- a critical transition point during the mid-20th century after which our civilisation experienced accelerated technological development, rapid population growth, and increased consumption of resources.
As the researchers write in their study:
These have combined to result in increased use of metals and minerals, fossil fuels, and agricultural fertilisers and increased transformation of land and nearshore marine ecosystems for human use. The net effect has been a loss of natural biomes to agriculture, cities, roads, and other human constructs and the replacement of wild animals and plants by domesticated species to meet growing demands for food.
Consequently, the researchers point to the 1950s and 1960s as the true start to the Anthropocene; our civilizational residue has become -- and is increasingly becoming -- a pervasive and persistent part of the geological record.
As Zalasiewicz explained, "There are an array of markers associated with previous epochs that make post-mid-20th century strata distinguishable from older strata."
Millions of years from now, the traces of our civilisation will be found buried in the geological record, and will include stratigraphic layers filled with concrete, elemental aluminium, plastics, and other characteristically human byproducts. Geologists of the future -- or perhaps extraterrestrial archaeologists, for that matter -- will also find signs of carbon particulates from atmospheric pollution, abnormally elevated levels of nitrogen and phosphorus from fertilisers and pesticides, and the radionuclide fallout from nuclear weapons. Other signatures will include dramatic changes to coastal sedimentation, and signs of widespread species extinction.
Increased rates of vertebrate extinctions. (Credit: C. N. Waters et al., 2015/Science)
Some of these "signals", explains Zalasiewicz, are simply markers, such as radioactive fallout. But others signal more pervasive change, while still others are effectively irreversible, such as the "homogenization" of the biosphere through invasive species. Taken together, they all characterise strata -- prompting scientists to consider the onset of a new geological era.
"Geological time units, including epochs, are typically established around systematic changes to stratal characteristics that typically reflect changes to the earth system of one form or another," said Zalasiewicz. In other words, evidence of human activities is being stamped onto rocks, sediments, and glacier ice.
For comparison, consider the Carboniferous period. This era, which began about 358 million years ago, marked time when trees grew across all the planet's land masses. After these trees died, they left a distinctive carbon footprint in the geological record, hence the term "Carboniferous."
The Anthropocene Epoch, should it become formally recognised, will become one of many epochs in the Quaternary period, which began 2.6 million years ago. "Not only would this represent the first instance of a new epoch having been witnessed firsthand by advanced human societies," the authors conclude, "it would be one stemming from the consequences of their own doing."
Yet some scientists have raised objections to the formalization of the term. It's possible that the greatest changes to the planet, and thus the strata, are still to come, such as the long term effects of global warming and rising sea levels. Others complain that the Anthropocene characterises a painfully brief geological interval of time.
"These are all legitimate points," said Zalasiewicz, "but it's worth pointing out the scale speed, diversity and (in many cases) long-lived nature or irreversibility of the changes related to the Anthropocene." He admits that the Anthropocene could be a short-lived era, one that will most certainly evolve over time, particularly as human influences accelerate and spread, and in consideration of future technologies. Regardless, Zalasiewicz said that nothing will "take us back to the Earth of the Holocene or of previous times." The key point is that the Earth is now evolving along a new trajectory, and there's "bound to be an evolution of different states", which is true of previous major changes to the Earth system.
The timing of this study is not an accident. Back in 2013, the Anthropocene Working Group submitted a proposal to the International Commission on Stratigraphy to formally accept the term. This proposal is scheduled to be reviewed by the ICS later this year. From there it's expected to be a long and hard process. Should it be accepted by the Subcommission on Quaternary Stratigraphy and the ICS itself, it will still have to be ratified by the International Union of Geological Sciences.
The group plans on carrying out further analyses, and addressing board responses to their new and previous papers. And as Zalasiewicz told Gizmodo, his team has further manuscripts in preparation, and they're working to summarize available evidence and provide interim recommendations by mid-2016.
Read the entire study at Science: "The Anthropocene is functionally and stratigraphically distinct from the Holocene".