These "chemical signals" at a specific depth in the Earth's upper crust are unique to the modern era, he said.

Altering official categories of Earth history is no small matter. Debates are still raging in geological circles over when, precisely, the Holocene began and the Pleistocene (popularly known as the Stone Age) ended. Another battle is being waged over when, exactly, the Tertiary gave way to the Quaternary about 1.9 million years ago.

And it's been that way, according to scientists, for about 11,700 years - a discernible boundary in the Earth's history that is marked, among other ways, by evidence of meltwater lakes and gravel ridges left across the Canadian landscape when the glaciers retreated at the end of the last ice age.

All of recorded human history has taken place within the Holocene, which textbooks and encyclopedias explain is still unfolding today.

But now, a distinguished group of British geologists has provocatively proposed that the Holocene is over and that we have entered a new geological era - the Anthropocene - in which humans have left such a distinctive footprint on the Earth's surface through carbon pollution, nuclear fallout, urbanization and other traces of our immense technological power that it should be officially recognized by international scientific bodies as "a formal epoch."

"Since the start of the Industrial Revolution, Earth has endured changes sufficient to leave a global stratigraphic signature distinct from that of the Holocene . . . encompassing novel biotic, sedimentary and geochemical change," the scientists state in February's cover story of GSA Today, a flagship publication of the Geological Society of America.

"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 scientists insist they are not simply performing a political stunt to bolster arguments for the rapid reduction in greenhouse gases to avert cataclysmic climate change.

They say proof of humanity's impact on the environment is now so great that - in keeping with scholarly tradition - the International Commission on Stratigraphy and its parent agency, the International Union of Geological Sciences, should declare a new boundary between the Holocene and the Anthropocene.

"We are now living in a new time period when the human modification of the system is so great, we need some way of recognizing that," Mark Williams, a University of Leicester paleobiologist and co-author of the article, told Canwest News Service on Tuesday.

He said the Anthropocene could be pegged as beginning with the Industrial Revolution some 200 years ago, "when human industrial processes started to transform the planet on a colossal scale."

He said distinctive increases in carbon dioxide deposits in Arctic and Antarctic ice cores or traces of radioactivity from nuclear weapons tests beginning in the mid-20th century - and which can be found all over the world - could be used to peg the beginning of the Anthropocene.

These "chemical signals" at a specific depth in the Earth's upper crust are unique to the modern era, he said.

Altering official categories of Earth history is no small matter. Debates are still raging in geological circles over when, precisely, the Holocene began and the Pleistocene (popularly known as the Stone Age) ended. Another battle is being waged over when, exactly, the Tertiary gave way to the Quaternary about 1.9 million years ago.

Those battles, though, are confined to the rocks-and-minerals crowd. A declaration that the Holocene is over and the Anthropocene has begun would send a powerful message to all of humanity that people and their machines - more than climate patterns or seismic activity or ocean currents or other non-human forces - are now the prime actors in changing the face of the Earth.

"It's an interesting idea," said James Ogg, a Purdue University geologist and an executive member of the ICS. "It's very important in that it does bring out that we have become a major geological agent."

Ogg said he is "doubtful" the proposal for a separate epoch would be ratified by the world body, but he suggests that formally declaring the Anthropocene a distinctive "phase" of the Holocene is a possibility.

"When I look out the window, what I see is all man-made material."