Maybe the Anthropocene started when mankind invented farming, ten or twelve thousand years ago? That was a big deal, but we were still relative pipsqueaks. How about 1492, when for better or for worse humans and their stuff went global courtesy of the heroic/evil (you choose) and rather ill-tempered Christopher Columbus. Maybe 1712, with the invention of the coal-powered steam engine in England. Or did our dominion begin in 1859 with the first oil well in Pennsylvania? Perhaps 1913, when Henry Ford's Model T assembly line gave fossil-fuel burning a turbo boost. Many scientists put a pin in 1945, when the first atomic bomb exploded in Alamogordo, New Mexico, and henceforth a radiometric signature from nuclear testing appeared as a thin line in the geological strata.
If awareness is the key factor, then Congressional hearings in the 1980s put the idea of climate change into the public sphere, or perhaps Al Gore's 2006 documentary film An Inconvenient Truth should get the credit. Need a number? Let's start the Anthropocene in 2014 when atmospheric concentrations of CO2 passed 400 ppm (parts per million). A year later the world banded together in Paris to sorta, kinda agree to limit greenhouse gas emissions, on a completely volunteer basis.
Or we could make it today -- fresh start!
Before that photo, the world outside one's door seemed an endless, infinite sprawl. Even with our maps, who could fathom it no less make a dent in it? But after that photo, the world acquired undeniable borders. We saw it as it was, all of it. Look everybody, there's Earth, hanging in space like a Christmas ornament. Really -- Earth! So beautiful and round and oddly vulnerable. What a gem. Try this: you can put your thumb over it and it's gone.
Then maybe some folks started thinking, hey, wait a second, let’s stop screwing it up. And with apologies to grouchy Columbus and the steam engine, so began the Anthropocene.