The Pleistocene "land grab"

2 minute read

Holy stratigraphy, Batman!

The International Commission on Stratigraphy (ICS) has elected to formally define the base of the Quaternary at 2.6 million years before present, and also to lower the base of the Pleistocene an epoch that encompasses the most recent glaciations from its historical position at 1.8 million years to 2.6 million years ago. The decision, finalized on 21 May, will now be passed to the executive committee of the International Union of Geological Sciences (IUGS) for ratification, which is expected in the next month or two.
The vote shifts an 800,000-year slice, formerly part of the Pliocene epoch, into the Pleistocene. "It's kind of a land grab," says Philip Gibbard, a geologist at the University of Cambridge, UK, who has fought for the redefinition since 2001. "But we see it as just putting straight a mistake that was made 2530 years ago."

The linked article in Nature, by Amanda Mascarelli, likens the change to the astronomers’ redefinition of Pluto. I’d say!

The geologists don’t like the existing Pliocene-Pleistocene boundary because there’s no major extinction or faunal turnover then. Many don’t like “Quaternary” at all, having largely done away with the associated “Primary” and “Secondary”. But Quaternary remains useful as a way to lump Pleistocene and Holocene. So, they’ve decided to redefine based on the initiation of the recent ice age cycles. That makes geological sense, but means that people have to relearn a bunch of stuff.

What impact will it have on paleoanthropology? Well, I suppose for one thing, we don’t have to talk about “Plio-Pleistocene” anymore. That term was most common as applied to sites and specimens between 2.5 and 1.4 million years ago. Sometimes people used it in the broader sense of all australopithecines and early Homo, but since we’ve had Miocene hominids for the last ten years, I think we can toss it out. Since the earliest credible specimens of our genus are around 2.5 million years old, Homo will henceforth entirely a Pleistocene phenomenon.

In fact, in terms of hominid evolution, 2.6 million years ago is a convenient place for the Pliocene-Pleistocene boundary. It’s certainly easier than shifting to use hominin instead of hominid. The question is whether the geologists will allow the Early Pleistocene to span all the way from 2.6 to 0.8 million years ago, or whether they’ll come up with some other terminology. Because it will be an enormous pain if we have to change the labels everywhere that refer to “Middle Pleistocene”.


Mascarelli AL. 2009. Quaternary geologists win timescale vote. Nature 459:624. doi:10.1038/459624a