January 28, 2011

The edges of historical or geological eras tend to be fuzzy. Humans existed when the Pleistocene ended and the Holocene began, 11,500 years ago. Among scientists, there is now serious talk that the Holocene has ended and a new era has begun, called the Anthropocene, a term first used in 2000 by Paul Crutzen, who shared a Nobel Prize for his work on the chemical mechanisms that affect the ozone layer. The Royal Society has devoted a recent issue of its Philosophical Transactions to the Anthropocene. According to one of the papers, the name is “a vivid expression of the degree of environmental change on planet Earth.” It means that human activity has left a “stratigraphic signal” detectable thousands of years from now in ice cores and sedimentary rocks. Those of us alive today may well be able to say we were present when the Anthropocene epoch was formally named. But we will not be able to say we were present at the start of the Anthropocene. There is a strong case that the Anthropocene begins with the Industrial Revolution, in the early 1800s, when we began to exert our most profound impact on the world, especially by altering the carbon content of the atmosphere. Other species are embedded in the fossil record of the epochs they belong to. Some species, like ammonites and brachiopods, even serve as guides, or index fossils, to the age of the rocks they’re embedded in. But we are the only species to have defined a geological period by our activity, something usually performed by major glaciations, mass extinction, and the colossal impact of objects from outer space, like the one that defines the upper boundary of the Cretaceous. Humans were inevitably going to be part of the fossil record. But 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.