Tuesday, January 29, 2008

Anthropocene - an epoch that reflects human impact on Earth's history

The last ~10,000 years of the Earth's history, since the end of the "ice age" is called the Holocene epoch in the geological time scale. Likely proposed by Sir Charles Lyell in 1833, the Holocene was adopted by the International Geological Congress in 1885.

This it includes the period that covers all of human civillisation. Since then, mankind's activities have been so so impactful to the planet's climate and ecosystems as to be geological in nature.

In 2000, Paul Crutzen and Eugene Stoermer suggested that this influence of human behavior on the Earth constituted a new geological era, the "Anthropocene". ["The "Anthropocene"," by Paul J. Crutzen & Eugene F. Stoermer. Global Change Newsletter, 41: 17-18.]

Summarising previous observations of human impact in the literature and examples of the many global impacts, the authors then say,

"Considering these and many other major and still growing impacts of human activities on earth and atmosphere, and at all, including global, scales, it seems to us more than appropriate to emphasize the central role of mankind in geology and ecology by proposing to use the term "anthropocene" for the current geological epoch. The impacts of current human activities will continue over long periods."

They proposed the later part of the 18th century as the starting point, from when global effects become noticeable.

GSA Today just published a paper that makes an argument for its consideration as a formal epoch. The team of British geologists, all members of the Stratigraphy Commission of the Geological Society of London, ask, "Are we now living in the Anthropocene?"

"The term Anthropocene, proposed and increasingly employed to denote the current interval of anthropogenic global environmental change, may be discussed on stratigraphic grounds.

A case can be made for its consideration as a formal epoch in that, since the start of the Industrial Revolution, Earth has endured changes sufficient to leave a global stratigraphic signature distinct from that of the Holocene or of previous Pleistocene interglacial phases, encompassing novel biotic, sedimentary, and geochemical change.

These changes, although likely only in their initial phases, are sufficiently distinct and robustly established for suggestions of a Holocene-Anthropocene boundary in the recent historical past to be geologically reasonable.

The boundary may be defined either via Global Stratigraphic Section and Point ("golden spike") locations or by adopting a numerical date.

Formal adoption of this term in the near future will largely depend on its utility, particularly to earth scientists working on late Holocene successions. This datum, from the perspective of the far future, will most probably approximate a distinctive stratigraphic boundary."

- Zalasiewicza, J, M Williams, A Smith, TL Barry, AL Coe, PR Bown, P Brenchley, D Cantrill, A Gale, P Gibbard, FJ Gregory, MW Hounslow, AC Kerr, P Pearson, R Knox, J Powell, C Waters, J Marshall, M Oates, P Rawson & P Stone, 2008. Are we now living in the Anthropocene. GSA Today, 18 (2): 4-8.

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