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The Quaternary Refuses to Die

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Quaternary, 2009 version

The Quaternary Period in today's geologic time scale

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Whenever geologists meet, you will soon hear the word Quaternary ("qua-TERN-ery"). It is the label for the most recent part of Earth history, when ice ages came and went and humans evolved rapidly into Homo sapiens. The name survives from the earliest days of geology, and hundreds of scientific societies, university departments, journals and conferences are devoted to it. Quaternary research is an important and vibrant branch of geology. But when the Quaternary Period vanished in the latest standard time scale of geology in 2004, the world's Quaternarists seemed to be caught flat-footed. It took them five years to right the wrong.

Who Spiked the Quaternary?

The International Commission on Stratigraphy (ICS) gave itself until 2008 to remake the geologic time scale into one suitable for a world standard. ICS subcommissions exist for many geologic periods, including the Quaternary. Their job is to set boundaries: exact points in time—and actual sections of rock where those points in time can be nailed down. These Global Stratotype Sections and Points, or GSSPs, have inevitably picked up the name "golden spikes."

This sensible-sounding concept is actually a wrenching change in geologic timekeeping. Historically, different specialists essentially had their own separate time systems.

  • Paleontologists based time scales on various fossil organisms in sedimentary rocks: conodonts, trilobites, foraminifers and other plankton groups, land vertebrates, pollen grains and many more have their own named ages.
  • Paleomagneticians used patterns of geomagnetic field reversals in igneous rocks and the oceanic crust.
  • Geochemists used numerical (absolute) dates derived by isotopic methods in rocks of all types and ages.
  • Geophysicists worked out the Earth's long-scale orbital cycles and, together with paleontologists, matched them to the detailed records of seafloor sediment.

When these specialists began integrating their work, the lack of a universal yardstick for geologic time became a serious problem. The golden spike is meant to stitch together the different tape measures at definitive points.

The GSSP system is guaranteed not to satisfy everyone, because no one locality is good for all dating methods and all methods are not equally suited for a given time period or material. Scientists of any stripe are not natural compromisers, either. But once they're won over, geologists find ways to make the golden spike system work.

The Dawdlers Protest

Despite its high-sounding description, the ICS's mission is a low-budget effort that proceeds, as most international volunteer projects do, in motley fashion. Dealing with the subcommissions involves a lot of nagging, email exchanges and adjustments of deadlines.

Quaternary specialists were the worst of the dawdlers, but (probably) not because they have unusual personalities. The Quaternary time period is like a structure that was built before the property lines were surveyed. By convention, the Quaternary consists of the Pleistocene and Holocene epochs, but at its root it signifies the time of recent ice ages. We now know that these ice ages began about 2.5 million years ago. Unfortunately, that time was well before the beginning of the Pleistocene, in the Pliocene Epoch. And the Quaternary, from the day Giovanni Arduino introduced the concept in 1759, was never formally defined or ratified.

The ICS meanwhile proceeded with its already-approved time unit, the Neogene Period, which begins about 23 million years ago. There was a chance to deal with the Quaternary in 1985, when the Pleistocene GSSP was ratified, and again later when the Pliocene was nailed down, but Quaternarists missed the boat. In fact the Neogene subcommission took over the Quaternary subcommission in 2001, a move that did not solve things (its annual reports have whiffs of exasperation). The ICS gave fair warning, but when the deadline came in 2004 there was still no official, ratified time unit of Period rank after the Neogene. At that point the ICS bulldozed the Neogene all the way to the present, wiping out the Quaternary. When the ICS quickly issued large posters and published a book cementing this decision, the move might have seemed a bit intimidating.

Quaternary geologists erupted in consternation (a CamQua newsletter from 2004 (PDF) is a good example). Soon the ICS and the International Union for Quaternary Research formed a joint committee that proposed changes in 2005, and a flurry of consultations followed. A new proposal eventually emerged: extend the Pleistocene Epoch back to include the Gelasian Age, put this larger Pleistocene into the Quaternary Period, and insert the Quaternary after the Neogene Period.

The matter was formally discussed at the International Geological Congress in Oslo, in August 2008. And in May 2009 the ICS accepted this proposal. When the International Union of Geological Societies later accepted the ICS ruling, the Quaternary returned to life. Now it's back in the Cenozoic where it always belonged.

PS: Quaternary research's geologic timekeeping is already past the GSSP system: So many different dating methods are cross-correlated and accurate for this period that the entire Quaternary Period, in effect, is full of golden spikes, a veritable golden age. In that light, Quaternary workers already had an ideal time scale. Maybe they were waiting for the ICS to catch up.

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