What geologists choose to call a period of history normally matters little to the rest of mankind; tussles at the International Commission on Stratigraphy over the boundaries of the Ordovician era do not normally capture headlines. The Anthropocene is different. It is one of those moments where a scientific realisation, like Copernicus grasping that the Earth goes round the sun, could fundamentally change people's view of things far beyond science. It means more than rewriting some textbooks. It means thinking afresh about the relationship between people and their world and acting accordingly.
Thinking afresh is the easier bit. Too many natural scientists embrace the comforting assumption that nature can be studied, indeed should be studied, in isolation from the human world, with people as mere observers. Many environmentalists—especially those in the American tradition inspired by Henry David Thoreau—believe that “in wilderness is the preservation of the world”. But the wilderness, for good or ill, is increasingly irrelevant.
Almost 90% of the world's plant activity, by some estimates, is to be found in ecosystems where humans play a significant role. Although farms have changed the world for millennia, the Anthropocene advent of fossil fuels, scientific breeding and, most of all, artificial nitrogen fertiliser has vastly increased agriculture's power. The relevance of wilderness to our world has shrunk in the face of this onslaught. The sheer amount of biomass now walking around the planet in the form of humans and livestock handily outweighs that of all other large animals. The world's ecosystems are dominated by an increasingly homogenous and limited suite of cosmopolitan crops, livestock and creatures that get on well in environments dominated by humans. Creatures less useful or adaptable get short shrift: the extinction rate is running far higher than normal geological periods.