News Notes
Geologic time
Tertiary is toast

It’s gone. A glance at the geologic time scale on the International Commission on Stratigraphy (ICS) Web site proves it: The Tertiary is no longer there.

The Tertiary marked the window from 65 million years ago to 1.8 million years ago, encompassing the Paleogene and Neogene. It leant its name to the so-called K-T (for Cretaceous-Tertiary) boundary, the extinction event associated with the disappearance of the dinosaurs. But from now on, ICS (the committee of the International Union of Geological Sciences that is responsible for setting geologic names and dates) wants you to use K-P, for the equivalent time periods Cretaceous and Paleogene.

Look between the Cretaceous and the Quaternary: You won’t find the Tertiary. Image courtesy of the International Commission on Stratigraphy.

“’Tertiary’ today is really not used as a formal term,” says James Ogg, a stratigrapher at Purdue University in Indiana who is Secretary-General of ICS. “At one time, there was a Primary, Secondary, Tertiary and Quaternary,” he says. Though the first and second terms disappeared as the stratigraphic record dictated new boundaries according to early forms of life, the Tertiary and Quaternary remained in common use. The Quaternary shouldn’t be in service either, Ogg says, even though it “is useful because it refers to climate swings” associated with glaciations. Still, Ogg and his colleagues prefer the Pleistocene and Holocene.

“From the time of Charles Lyell, [the Tertiary was] never properly defined,” says Cinzia Cervato, a biostratigrapher at Iowa State University in Ames, who works with Ogg on CHRONOS, a National Science Foundation project to develop an online database for stratigraphic time. Defining a time period requires gathering together fossil, paleomagnetic and other records. Such precise dating physically places the beginning and end (or top and bottom) of a geological time window in the worldwide stratigraphic record.

“I will feel some nostalgia for the K-T boundary,” says Walter Alvarez, a geologist at the University of California, Berkeley, who may be most responsible for bringing the term into common use. He and his co-workers linked a meteor impact’s detritus at that time boundary to the death of the dinosaurs.

Although Alvarez probably will continue to use “K-T,” “being grandfathered in so to speak,” he says that when a decision is made like that by ICS, it “is almost always a good idea.” And, he emphasizes, without the international naming mechanisms, “we would be absolutely lost.”

Along with other new stratigraphic guidelines, ICS will publish its reasoning on nixing the Tertiary, through Cambridge
University Press next summer.

Naomi Lubick

International Commission on Stratigraphy (ICS)

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