David Grinspoon writes: As a planetary astrobiologist, I am focused on the major transitions in planetary evolution and the evolving relationship between planets and life. The scientific community is converging on the idea that we have entered a new epoch of Earth history, one in which the net activity of humans has become an agent of global change as powerful as the great forces of nature that shape continents and propel the evolution of species. This concept has garnered a lot of attention, and justly so. Thinking about the new epoch – often called the Anthropocene, or the age of humanity – challenges us to look at ourselves in the mirror of deep time, measured not in centuries or even in millennia, but over millions and billions of years. And yet much of the recent discussion and debate over the Anthropocene still does not come to terms with its full meaning and importance.

Various markers have been proposed for the starting date of the Anthropocene, such as the rise in CO2, isotopes from nuclear tests, the ‘Columbian exchange’ of species between hemispheres when Europeans colonised the Americas, or more ancient human modifications of the landscape or climate. The question in play here is: when did our world gain a quality that is uniquely human? Many species have had a major influence on the globe, but they don’t each get their own planetary transition in the geologic timescale. When did humans begin changing things in a way that no other species has ever changed Earth before? Making massive changes in landscapes is not unique to us. Beavers do plenty of that, for example, when they build dams, alter streams, cut down forests and create new meadows. Even changing global climate and initiating mass extinction is not a human first. Photosynthetic bacteria did that some 2.5 billion years ago.

What distinguishes humans from other world-changing organisms must be related to our great cleverness and adaptability; the power that comes from communicating, planning and working in social groups; transmitting knowledge from one generation to the next; and applying these skills toward altering our surroundings and expanding our habitable domains. However, people have been engaged in these activities for tens of thousands of years, and have produced many different environmental modifications proposed as markers of the Anthropocene’s beginning. Therefore, those definitions strike me as incomplete. Until now, the people causing the disturbances had no way of recognising or even conceiving of a global change. Yes, humans have been altering our planet for millennia, but there is something going on now that was not happening when we started doing all that world-changing. [Continue reading…]