Human touch.
Rapid deforestation, shown here in Brazil, is just one way that people are rapidly changing the planet.

Human-Driven Planet: Time to Make It Official?

A group of geologists has formally proposed designating a new geologic epoch, the Anthropocene, which would encompass the past 200 years or so of geologic history. The action is appropriate, say the authors, because during the past 2 centuries, human activity has become the primary driver of most of the major changes in Earth's topography and climate.

Each stratigraphic layer in the geologic record reflects the conditions of the time it was deposited and offers a glimpse into Earth's past. Researchers have painstakingly pieced together this geologic history, differentiating the layers into classifications of various duration called eons, eras, periods, epochs, and ages that reflect characteristic conditions. For example, the Carboniferous period, which lasted from 360 million to 300 million years ago, is known for the vast deposits of coal that formed from jungles and swamps. Indeed, even some of the longer stretches have been named based on biology, such as the Paleozoic ("old life") and the Cenozoic ("recent life").

Earth has been subject to the same kinds of physical forces--wind, waves, sunlight--throughout the planet's existence. But life has been much more varied in its impact. The appearance of oxygen-producing photogenesis, the rise of land plants, and many other evolutionary events have shaped the planet in dramatic ways. And now--humans. In the past 200 years, ever since the human population reached 1 billion, the use of fossil fuels, the growth of metropolises, and other influences have begun to affect the stratigraphic process, altering the physical and chemical nature of ocean sediments, ice cores, and surface deposits. So now a group composed mostly of British scientists wants to amend the geological record to accommodate that change.

In the February issue of GSA Today, which is published by the Geological Society of America, geologist Jan Zalasiewicz of the University of Leicester in the U.K. and colleagues argue that the International Commission on Stratigraphy should officially mark the end of the current epoch. That would be the Holocene ("entirely recent"), which started after the end of the last ice age, about 10,000 years ago. The newest and most entirely recent epoch, postmodern as that sounds, should be the Anthropocene, the group argues.

As evidence, the researchers cite an assortment of trends from the beginning of the Holocene to the present. These trends show clear signs--some of which have become apparent in the geological record--of human-induced alterations. Since about 1800, lead concentrations in water and soil have increased dramatically, carbon dioxide has flooded the atmosphere, and dams have trapped untold amounts of sediment. All of these processes now vastly outpace the equivalent natural forces. "A reasonable case can be made for the Anthropocene as a valid formal unit," Zalasiewicz says.

The argument has merit, says geologist Richard Alley of Pennsylvania State University in State College. "In land, water, air, ice, and ecosystems, the human impact is clear, large, and growing," he says. "A geologist from the far distant future almost surely would draw a new line, and begin using a new name, where and when our impacts show up."

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