With climate change, concrete deserts and agriculture, human beings have fundamentally altered the face of the Earth. But have we really ushered in a new geological era, the so-called Anthropocene?

Paul Crutzen, winner of the Nobel Prize in chemistry, finds it hard to believe. "It's incredible to see what a single word changes," he says. Crutzen coined the word "Anthropocene," Greek for the "recent age of man," 12 years ago at a scientific conference in Mexico. He used the term as a way of describing radical change in nature, saying that man's influence on the environment was now so overwhelming that a new epoch -- the "Anthropocene" -- had begun.

For some geologists, the proposal has been nothing less than revolutionary, and an unwelcome challenge. Indeed, it has unleashed a heated debate that has now spilled over from the scientific world into the public realm. Newspapers and magazines are proclaiming the advent of the "age of man" on their cover pages, artists are invoking the Anthropocene and even German governmental advisers have adopted the term.

Indeed, there are many who are enthusiastic about the defining of a human epoch. As an editorial from late February in the New York Times put it, the "true meaning of the Anthropocene is that we have affected nearly every aspect of our environment -- from a warming atmosphere to the bottom of an acidifying ocean." According to the British news magazine The Economist, humans "have become a force of nature reshaping the planet on a geological scale." Indeed, a recent edition of the magazine bore the title "Welcome to the Anthropocene" on its cover page above a picture of a globe being constructed by humans from within.