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A Time War Over the Period We Live In

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Science  25 Jan 2008:
Vol. 319, Issue 5862, pp. 402-403
DOI: 10.1126/science.319.5862.402

Like astronomers battling over the status of Pluto, geoscientists are revving up to settle the fate of the interval of time known as the Quaternary, as well as the status, some feel, of an entire field.

Like astronomers battling over the status of Pluto, geoscientists are revving up to settle the fate of the interval of time known as the Quaternary, as well as the status, some feel, of an entire field

The real quaternarists.

Study of the Quaternary includes the environment of early humans.

CREDITS (TOP TO BOTTOM): RICHARD HOOK/GETTY IMAGES

The dinosaurs had their Cretaceous period and the reptiles their Jurassic, but for 200 years now, humans have not agreed on what period of geologic time we are living in. It could be the Neogene period. On many geologic time scale charts, the Neogene runs from 23 million years ago to the present. Or it could be the Quaternary. “The Quaternary is the most important interval of geologic history,” says John Clague, former president of the International Union for Quaternary Research (INQUA). On some charts, the Quaternary spans the last couple of million years of time, including when humans took up tools and the world began slipping into icy climatic gyrations.

Depending on the time scale considered, the Quaternary sometimes takes a position of pride following the Neogene period. But other times it's relegated to sideshow status, and sometimes it's even absent entirely. Indeed, in recent years, the International Commission on Stratigraphy (ICS) “abolished” the Quaternary, according to riled quaternarists. “They tried to suppress it while no one was looking,” says Philip Gibbard of the University of Cambridge in the U.K. “They nearly got away with it, [but] we were not going to have it.” The Quaternary “is a manifestation of our community,” adds Clague. “We don't want anyone denigrating that.”

Take your pick.

The Quaternary has been variously portrayed in a secondary status (left), as a subera (middle), and as a period (right).

SOURCE: MODIFIED FROM A GEOLOGIC TIME SCALE 2004; M.-P. AUBRY ET AL., EPISODES 28, 1 (JUNE 2005); ICS PROPOSAL TO IUGS

Now these geoscientists are heading for a showdown over the Quaternary. At the next quadrennial International Geological Congress this August in Oslo, Norway, the community will consider an ICS proposal that would enshrine the Quaternary as a full-fledged period encompassing 2.6 million years expropriated from the young end of the Neogene. But there are rules for dividing up time, notes marine geologist William Berggren of Rutgers University in Piscataway, New Jersey—rules that yield a consistent and therefore useful common language among geologists. And the quaternarists aren't following them, he says. “This is not going to happen.”

A matter of time …

Geologists have divvied up time for the sheer convenience of it ever since the late 18th century, when they began to realize just how much of it there was, but the formal rules for dividing the geologic time scale started emerging only in the mid-20th century. Most fundamentally, the divisions must be hierarchical—a whole number of the smallest units of time constitute a single unit at the next higher level, and so on. And the boundaries between units must be recognizable worldwide, not just at a few special places. Conflicts between such modern rules and divisions that evolved over centuries linger into the early 21st century.

The Quaternary came into usage 2 centuries ago as the most recent of four divisions of the fossil record of life: the Primary, Secondary, Tertiary, and Quaternary. Geologists generally used Quaternary to refer to the loose soil and sediment moved around by the glaciers of the ice ages. That sediment held a distinctive set of fossils, living representatives of which are still common. But, Primary and Secondary fell out of use long ago, supplanted by other names. In recent decades, ICS—with the consent of the International Union of Geological Sciences (IUGS), the world's ruling body on such matters—dropped the Tertiary as well. Now, the Quaternary name “doesn't make any sense,” concedes Norman Catto of Memorial University of Newfoundland in St. John's and editor-in-chief of Quaternary International. “It's the fourth division of a system in which the other three divisions have been thrown out.”

The Quaternary may be a lingering anachronism, but “the name is less important than the concept,” says Catto. “We have the strong [early] human element involved. That sets it apart. And it's defined as a time of glaciation.” Indeed, many INQUA researchers are, strictly speaking, not geologists but anthropologists, climatologists, glaciologists, or paleoecologists, he says, specialists who are not attuned to the niceties of the modern geologic time scale.

Even as the term “Quaternary” was coming into use, however, another, slightly different interval of time with a different name was also becoming identified with the ice ages. In 1839, a founder of modern geology, Charles Lyell, dubbed what turned out to be the past 1.8 million years the Pleistocene (“most recent”). He defined the interval on the basis of a distinctive set of fossil mollusks; many of those species are still around today.

CREDITS (LEFT TO RIGHT): COURTESY OF WILLIAM BERGGREN; COURTESY OF PHILIP GIBBARD

But unlike the Quaternary, Lyell's Pleistocene eventually became firmly incorporated in the emerging, official geologic time scale. In 1983, after 35 years of dickering in the community, a joint INQUA-ICS working group defined the beginning of the Pleistocene as that point in an outcrop of marine sediment at Vrica in southern Italy where several species of microfossils make their first or last appearance in the geologic record. Earth's magnetic field flipped about then, too; the reversal is recorded in the sediments around the world. The community drove the “golden spike,” as the marker of a geologic boundary is called, at Vrica because its fossil transitions could be recognized far beyond Italy. Geologists working around the world could tell just where in the geologic record they were.

… or perspective

For the next decade or two, the Quaternary languished in the shadow of the Pleistocene. IUGS had ratified the golden spike at the beginning of the Pleistocene “isolated from other more or less related problems, such as … the status of the Quaternary,” as the formal IUGS announcement put it in 1985. And INQUA “was sleeping” through the 1990s, says Gibbard. He would soon change that.

In December 2001, Gibbard heard that a major scientific publication then in the works—A Geologic Time Scale 2004, 600 pages long, with 40 contributors, and co-sponsored by ICS—would give the Quaternary short shrift. In the book's accompanying wall chart, the Neogene period and its youngest subdivision—the Pleistocene epoch—reigned supreme. The Quaternary made just one appearance, on a separate plot of the comings and goings of the ice ages. It lost out because “partly to our surprise, it had no official rank [in the hierarchy] or length,” says James Ogg of Purdue University in West Lafayette, Indiana, who prepared the chart with Felix Gradstein of the University of Oslo, Norway.

Although the time scale had no official scientific standing, Gibbard sprang into action. At his instigation, “INQUA said to IUGS we weren't going to take it from ICS,” Gibbard says. “ICS were told in no uncertain terms by IUGS they couldn't ignore the Quaternary community.” In response to the fracas, IUGS President Zhang Hongren of Beijing withheld IUGS's 2007 funding for ICS until ICS properly addressed the Quaternary problem.

And address the problem it did. “Now I think we've reached a pretty good compromise,” Ogg says. “We hope so.” The proposal gives the last 2.6 million years of the Neogene to an official Quaternary period, beginning about when world ocean circulation shifted and climate swings intensified in a cooling world. “We won a battle,” says Clague. “It goes beyond a name. It's about how people working in the Quaternary are perceived.”

To follow the rules, some cutting and pasting of the time scale will be required. In order to line up the beginning of the Quaternary with the beginning of the Pleistocene and thus maintain a proper hierarchy, an 800,000-year slice of the earlier Pliocene epoch will have to move up into the Pleistocene. Some geologists are incensed. “All of a sudden they want to move [the Pleistocene] down 800,000 years,” says marine geologist Lucy E. Edwards of the U.S. Geological Survey in Reston, Virginia. “Why? ‘Because we want it.’ It upsets the stability of the nomenclature without a good scientific reason. Many more marine geologists working in the Pleistocene would be completely discombobulated.”

Critics say the revision violates a basic rule: that boundaries on the time scale are not delineated by climate changes such as revved-up ice ages. Exactly when a climate event appears in the geologic record, they point out, can depend on the latitude where the record was laid down. Edwards says quaternarists would take the boundary to be “when the glaciation started where I work.” Marine geologist Marie-Pierre Aubry of Rutgers University plans to hold firm against the change. “Are we going to give up our principles?” she says. “I don't believe so.”

Proponents of the proposal point out that the proposal pegs the Quaternary's lower boundary to an extremely well defined climate event: a sharp swing recorded at the same time at all latitudes in marine-sediment oxygen isotopes. But it still doesn't pass muster with marine geologists. “Climate change is not a criterion for defining units except for quaternarists,” Berggren says. “They think climate change at 2.6 million years is the most important thing, [but] climate changes are not unique signals in the record.” Similar climate oscillations precede and follow the chosen swing, he notes, and major episodes of glaciation have occurred for hundreds of millions of years. “The rest of the community is going to ignore it,” he says.

The arguments will come to a head this August at the 33rd International Geological Congress in Oslo. “We're going to make time for an open forum and discussion,” says Peter Bobrowsky of the Geological Survey of Canada in Ottawa, who is secretary general of IUGS. “We hope to resolve the matter of the Quaternary [in Oslo] or agree on how to resolve it.” He says he expects a good outcome, if only because IUGS has ruled that nothing will be carved in stone before 2009. Oslo “could be a free-for-all,” he says. “It won't be a bloodbath. They are academics.”

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