Peter Hoey

We're all here. The newly official Quaternary period includes the span of our genus Homo as well as the comings and goings of the ice ages.

The Quaternary Period Wins Out

Dick writes about Earth and planetary science for Science magazine.

Geoscientists have cut the Gordian knot of geologic timekeeping. Ever since 19th century geologists divided the history of Earth into four periods—the Primary, Secondary, Tertiary, and Quaternary, oldest to most recent—their intellectual descendants have been dismantling that time scale. But the geologists, anthropologists, glaciologists, and paleoecologists studying the last couple of million years became quite attached to the Quaternary. They gave its name to their journals and even themselves—to the disgruntlement of strict constructionists, who have been insisting for decades that the modern rules for dividing up geologic time permitted neither the Quaternary nor quaternarists (Science, 25 January 2008, p. 402).

On 21 May, the final committee vote on the question was announced: The quaternarists will endure. Pending an almost certain ratification by the ultimate authority--the International Commission on Stratigraphy (ICS)--the Quaternary will officially take over the past 2.6 million years of the geologic time scale, when humans took up tools and the world began slipping in and out of the ice ages.

"The Quaternary Commission is greatly relieved and pleased," says Philip Gibbard of the University of Cambridge in the United Kingdom, who is president of the commission, a subgroup of ICS. Nomenclature "is not set in stone, even in geology," says Gibbard. "It's just a question of changing the label."

Not quite. "It makes no sense, it creates havoc, we're going to ignore it pretty much," says marine geologist Marie-Pierre Aubry of Rutgers University in Piscataway, New Jersey, who with others vociferously opposed the change. The ICS committee's 16-to-2 vote, she notes, not only usurps the last 2.6 million years of the Neogene period for the Quaternary but also extends the subsidiary Pleistocene epoch from 1.8 million years ago to 2.6 million years at the expense of its predecessor, the Pliocene epoch. Everyone had agreed on how to identify the original time boundaries according to consistent rules, she says; the vote throws those rules out the window. "You have to respect scientific principles," Aubry says. "If you don't, things don't make sense any more."

"Technically, [Aubry] is absolutely right, but I don’t think it's going to make a great deal of difference in our community," says paleoceanographer Lloyd Keigwin of Woods Hole Oceanographic Institution in Massachusetts, who was not involved in the debate. Researchers analyzing the marine record are usually concerned with changes through time, he says, not so much where an event stands in relation to broadly spaced time markers. "From a practical standpoint, we may have to move on," he concludes.

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