A recent crossword puzzle clue asking for the eon we inhabit made me realize that I didn’t know much about terms for times. It has become fashionable to say ours is the anthropocene era, with “anthropo” being the word for human, like anthropology is the study of humans, and “cene” being a word for a time stretch, though it literally means “new” in Greek. This is supposed to be a way to impress upon the word’s users the gravity of the fact that human activity is measurably changing the atmosphere at the planetary scale, per its coiners, Eugene Stormer and Paul Crutzen, a biologist and a chemist who came up with it in 2000. I dislike the word partly because I am actually optimistic about humanity’s ability to “solve” (that is: both mitigate and adapt to) climate change and also because I think the residents of any given epoch are unlikely to know from the inside it what it will look like in retrospect.

But all this got me thinking about these words, such as “Jurassic” and “paleo.” Where do they come from? They are, apparently, from something called geochronological time, through which we have chunked up the entire lifespan of Earth, some 4.54 billion years. Eons are longer than eras, which are longer than periods, which are longer than epochs. The shortest little ones are called ages, just a trifling few million years long. Are you ready to memorize your address? The name of the time you live in is, according to the International Union of Geological Sciences, as follows: the Phanerozoic eon, Cenozoic era, Quaternary period, Holocene epoch, Meghalayan age. Ages in geologic time are, of course, distinct from historical ages, like the Iron Age, which are something like a thousand years long.