Simon L. Lewis and Mark A. Maslin of University College London* point to the year 1610, marked by, of all things, a sharp but brief dip in carbon dioxide concentrations (revealed in ice cores). The greenhouse-gas decline, they say, is thought to have been the result of the implosion of civilizations in the Americas as European-carried diseases killed off tens of millions of inhabitants of the “New” World. The collapse of agriculture would have resulted in enormous regrowth of forests, and thus the uptake of CO2.I get it that geologists have their own rules of the game, but from a "real" perspective, the impact of humans began with the scientific discoveries leading to a fall in the death rate, and thus to the startling increase in the number of human beings living on the planet. Those same scientific discoveries--emanating generally from the European Enlightenment--are also at the core of innovations that have allowed us to change the earth's atmosphere in very measurable ways, and the layers of the planet beneath the surface in ways that are less readily measurable, but no less real in their consequences (e.g., water and mineral extractions). The mid-19th century is when these changes became readily apparent and they have been essentially unstoppable since then.
Another candidate for the beginning of the Anthropocene might be the year the world hit 2 billion people--estimated to be 1927. Why? Because multiple studies suggest that the world could sustain a population of no more than 2 billion people at the current level of living of the US and other rich nations.
A quick Google search of the term "anthropocene" shows that its use is spreading and that it resonates with a lot of people. It may or may not resonate with geologists, but I have a hunch the term is here to stay and with luck it will help to call attention to what we're doing to the planet before it's too late to save the human species.