The world today is undergoing rapid environmental change, driven by human population growth and economic development. This change encompasses such diverse phenomena as the clearing of rainforests for agriculture, the eutrophication of lakes and shallow seas by fertilizer run-off, depletion of fish stocks, acid rain, and global warming. These changes are cause for concern—or alarm—among some, and are regrettable if unavoidable side effects of economic growth for others. How significant are these changes in total? How might they evolve, and what might their ultimate consequences be? One way of studying these changes is to consider them as the latest phase of the many environmental changes that have affected the Earth since its origin, a little over four and a half billion years ago. Humans may be considered as geological agents, and anthropogenic environmental change may be compared with events in Earth’s deep history. Such analysis dates, perhaps surprisingly, from the earliest days of organized geological study. Working before the French Revolution, the Comte de Buffon wrote arguably the first evidence-based geological history of the world—_Les Époques de la Nature_, published in 1788 (Roger 1962): his seventh and final epoch denoted the time during which humans dominated and warmed (beneficially, Buffon...