There is a tradition in geology where a golden spike is inserted into a layer of rock, signifying the historical beginning, of different geologic events.
Andrew Revkin, in a October 16, 2014 New York Times Opinion blog, discusses his role in the Anthropocene Working Group, in which he comments on the complexities of defining a geologic era with a roomful of international scientists. Heady stuff.
You can read the entire article here.
