We live in the Anthropocene: For better or for worse, the Earth system now functions in ways unpredictable without understanding how human systems function and how they interact with and control Earth system processes. Regardless of whether this transition from the Holocene (generally thought of as the past 12,000 years) to the new epoch of the Anthropocene will ultimately be for the better or for the worse, the Earth system will not be returning to a preanthropogenic state for the foreseeable future.
Human involvement in the Earth system has now gone far beyond mere interference with “natural” processes. Human systems have emerged as new primary Earth systems, not only by dramatically altering preexisting natural processes but also, more important, by introducing a host of new Earth system processes entirely novel to the Earth system. As a result, the classic paradigm of “Earth systems with humans disturbing them” is obsolete. Human systems have become as integral and defining a component of this planet's processes as are biological, atmospheric, hydrologic, and geologic systems. As with the rise of photosynthetic organisms and the emergence of the biosphere, human systems have driven the Earth along a new and unprecedented path.