Redefining Quaternary

Blogging on EARTH

The Quaternary Period — the geologic time period that includes human evolution up to the present — is now a bit longer than it used to be.

A beloved term by many geologists, the Quaternary has long been used to refer to the two most recent epochs, the Pleistocene and the Holocene (the latter being the most recent 10,000 years). But some geologists (apparently, particularly marine stratigraphers) have considered Quaternary to be an outdated term that is part of a nearly extinct classification system for geologic time (remember the Primary and Secondary periods?) — and hoped to just fold it into the overall period "Neogene," which includes all of the last 23 million years.

Meanwhile, in the 1980s, the start date of the Pleistocene (and thus the Quaternary) was officially set at 1.8 million years ago. But the Quaternary scientists wanted to push it earlier by 800,000 years, slicing off the end of the Pliocene.

So last year, the International Commission on Stratigraphy once again addressed the long-standing debate. The commission began a year of proposals and discussions within the geoscience community on both issues, bring them both to a vote this year. And the Quaternary scientists won: Last month, the commission approved a redefinition proposal for the Quaternary, revising the start date to 2.6 million years ago.

Not everybody is happy with the decision, of course. And after revising them in the 1980s, USGS will have to once again revise its geologic maps.

Carolyn Gramling
Thursday, June 4, 2009 - 12:00