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30 November, 2011


In case you did not know, there is an International Commission on Stratigraphy. They decide the chronostratigraphic units that reckon our geological time. I'm not saying they deserve the entire credit, but without them, we'd be stuck in the Pleistocene, baby.

But here we are all smart and modern, in the Holocene Epoch, ever since 11,787 years ago this coming December 22. We know this because a shift in deuterium excess values was observed in the GRIP ice core in central Greenland, spelling the bitter end of the Younger Dryas cold period. Adios, Pleistocene, giant sloths, and dire wolves.

Many stratigraphic units are decided by extinctions, but more often of much smaller creatures than the megafauna that capture our imagination. This makes sense, because stratigraphers intent on finding minute changes tend to look in fine layers of sediment, and it's hard to squeeze a mastodon into one of those, not to mention the fact that for every giant mammal there are untold multitudes of rotifers. And when temperatures change, or atmospheric chemistry shifts, certain teeny species die, while others emerge from obscurity to fill new muds with their skeletons. The individual deaths and the mass extinctions were not for naught, though, because their ancient sacrifices have borne unto us just the sort of evidence we need that the earth changes, and is nearly a million times older than the stratigraphy-deprived biblical scholars used to tell us.

Not that the establishment of global stratigraphic units is completely automatic, uniformly legible to all geologists. I don't know enough of the ICS workings to state it as a fact, but I do have enough familiarity with academia to hypothesize that there exist disputes, heated disagreements, perhaps even feuds over just what comprises a certain boundary, or precisely how old it is. One area of disagreement I do know about has to do with the most recent epoch, on the candidacy of the Anthropocene.

"Cene" is the favored ending for stratigraphic series that define epochs, at least since the dinosaurs left the scene. "Anthropo" of course refers to the most hairless and arrogant of the great apes. So Anthropocene refers to a new chronostratigraphic unit corresponding to our presence on a scale that influences geology.

Not so quick, some of the ICS brethren say. Perhaps we are again over-estimating our importance, and geology will wipe us and our sediments away. But it looks to me like we've deposited enough concrete to make our mark.

Among the pro-Anthropocene contingent, there are various ways of reckoning its onset. Some argue for the beginning of agriculture as the threshold, since this is when humans really began altering soils and sedimentation, both with intentional acts like tillage and terracing, as well as mistakes and disasters ranging from burst irrigation reservoirs to the Dust Bowl. Personally, I think agriculture will prove to be too fluid a concept to nail down a global start date, besides which it may end up subsuming the entire Holocene and perhaps more, depending on how it is defined, and then what is the ICS to do? Backtrack? I think they'd rather not.

Other criteria abound. Such as the beginnings of cities, which create deposits of structures and artifacts that last long after they people move on or bury them under more stuff, as we are wont to do. Or, the wave of extinctions in our wake. Or, carry on with the atmospheric chemistry or global climate approaches that have defined other chronostrata--we've warmed the earth and perforated the ozone, isn't that enough to merit (to our own demerit, maybe) a human epoch? It took us a while to get to that point, but what about the creation of highly radioactive isotopes? It is no coincidence that the "present" in radiocarbon time is AD 1950, the years when enough atmospheric tests of nuclear bombs occurred to screw up any subsequent carbon dates.

Eventually, it won't matter what we say. Alien paleontologists will land on earth and reckon by their own system. They'll find a strata rich with large bipeds, and if they are lucky, they may find one of them clutching a laminated copy of the International Stratigraphic Chart.

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