[tt] anthropocene

[Eugen Leitl]

http://sciencenow.sciencemag.org/cgi/content/full/2008/124/1

Human-Driven Planet: Time to Make It Official?

By Phil Berardelli

ScienceNOW Daily News

24 January 2008

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."