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Andrew Alden

The Quaternary Is Back in the Ring

By May 26, 2009

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The wrangling over the geologic time scale is near an end, as the International Commission on Stratigraphy voted on May 22 to set a new version of the Quaternary Period in stone. Briefly, the long-used age term had been erased in the ICS's 2004 reorganization of the time scale, as far as I can tell because the Quaternary community simply missed the train. Widespread consternation followed, and the slow work of amending the new scale began. (See my article "The Quaternary Refuses to Die" for more background. I will add a new paragraph soon. I've posted other updates here, here, here, here and here.) Now a new definition that pleases nearly everyone is ready for formal acceptance by the International Union of Geological Societies.

After five years the stars and planets finally aligned (or maybe the better metaphor is the drifting of continents), and the most sensible proposal was finally ready: expand the Quaternary to encompass the glacial age starting 2.5 million years ago, which is what Quaternarists have always meant in their heart of hearts. To do that, have the Pleistocene Epoch engulf the latest age (the Gelasian) of the preceding Pliocene Epoch and put the newly expanded Pleistocene, with the Holocene, into the Quaternary. The vote was carried out by email and reported on the ICS's blog, an unusual glimpse into the workings of a scientific bureaucracy.

Commission member James Ogg ably summarized the proposal's virtues: "This will equate the beginning of the Pleistocene Epoch/Series with the historical use of Quaternary (beginning of first major continental glaciation; lowest widespread till and loess deposits, onset of traditional Ice Ages, etc.) as used by INQUA, Quaternary researchers and most geological survey maps. The Pliocene/Pleistocene boundary will correspond closely to a fundamental change in the operation of Earth’s ocean-climate system and in the evolution of terrestrial fauna-flora (including early humans). The series-boundary becomes a significant episode in Earth’s history, rather than the minor local Calabrian/Gelasian episode of migration of selected microfossils into the Mediterranean."

Marine researchers don't think much of the Quaternary because the seafloor record of the Cenozoic Era divides more cleanly into two periods, the Paleogene and the Neogene. Splitting the Quaternary out of the Neogene and having three Cenozoic periods would make the late Cenozoic somewhat more cumbersome to talk about. But that's the way it was for many years before 2004.

A few curmudgeons object to the Quaternary because of what the word itself means. The very first division of the world's (well, Italy's) rocks, by Giovanni Arduino in 1759, had Primary basement rocks, Secondary sedimentary rocks, Tertiary volcanics (or maybe it was the other way around) and Quaternary sediments. Why should we hang onto the remnants of this pitifully simplistic scheme today? The answer is, we aren't using them the way Arduino did, they're just nice old names that have precise meanings today. As long as the names don't occlude clear thinking, what's wrong with that? Seriously, no one actually thinks that glacial times are Earth's Fourth Age, but the rocks and records of Quaternary time do stand out and deserve a convenient, well-worn name.

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