You would think that, with 4.6 billion years of geologic history to play with, geologists wouldn’t get all hung up about a mere 2.6 million years. But when those 2.6 million years include the glacial episode popularly known as the Ice Ages (and the evolution of some weird naked ape), well… scientists can get pretty protective of their terminology.

Geological Society of America time scale

I’m neither a stratigrapher nor a historian of stratigraphy. (In fact, I tend to treat sedimentary layering as a marker that helps me keep track of the gorgeous changes in shape that rocks undergo.) I also don’t work with fossils – they don’t tend to survive metamorphism. But here’s my non-specialist understanding of what went on:

Stratigraphy – the layering of sedimentary rocks – was recognized before we knew about radioactivity, and before geochronologists started using isotopes (especially uranium and potassium – carbon’s half life is too short, unless you think the Earth is 6000 years old) to tell time. The original layers were known as Primary, Secondary, Tertiary, and Quaternary. But it turned out that the Primary and Secondary layers contained a huge amount of the history of the Earth (plus a lot of those rocks weren’t sedimentary at all), and the terms were abandoned a long time before I studied geology. (The Archean, Proterozoic, Paleozoic, and Mesozoic – nearly 4.5 billion years of time – fit into the Primary and Secondary rocks.)

The Tertiary and the Quaternary became, together, the Cenozoic: the Age of Mammals, all the stuff after the dinosaurs (and lots of other things along with them) got snuffed out. Here in the western US, we like the Tertiary, because it coincides with some big tectonic events: the Laramide Orogeny (and growth of the Rockies), the continental extension that gave us the Basin & Range Province, the formation of the San Andreas Fault… oh, and a lot of volcanic rocks. But the Quaternary has even more defenders. The Quaternary, traditionally, is the time since continental glaciers began to advance. In the world of potentially active faults, “Quaternary” means “we know it’s pretty young, but it hasn’t had an earthquake that we’ve measured… yet.” For volcanoes, Quaternary means “it’s pretty young, and maybe it could still be active, so maybe we should keep an eye on it.” (For a rock person, Quaternary also means “dirt.” Not that I use such perjorative words to refer to loose material stuck to my boots. At least, not most of the time.) There is a whole subfield of geology devoted to studying the landforms and climate change of the Quaternary, large enough that people call themselves “Quaternary geologists” and publish in journals like Quaternary Research. The term gets a lot of use.

So you can imagine what happened when the International Commission on Stratigraphy decided to abandon the term. (They had already gotten rid of the Tertiary while I was napping, or working on Paleozoic rocks, or something. It was replaced with the “Paleogene” and the “Neogene.”)

Robert Huber at Stratigraphy.net has news of ICS’s final decision: the Quaternary is back. There’s discussion on the ICS’s bulletin board here. The gist is that the Quaternary is going to be its own period, coming after the Neogene, and starting at 2.6 million years ago (which coincides with major global climate change). The Quaternary geologists have their period back, where when they wanted it. And it’s defined with the kind of rigor that should be workable in marine sediments. (People who have been using “Neogene” for sediments younger than 2.6 million years might be cranky, but they don’t have to give up the titles of their journals, at least.)

It also means that the ages used on the GSA timescale are correct. (Until someone comes along and renames something else. Or dates a boundary more precisely. Or something. Which will force me to print and laminate yet another time scale, and turn my old ones into bookmarks or placemats or something.)

I still wish that “Tertiary” hadn’t been abandoned, though. (Did we really need so many age names that start with “P”? Precambrian, Proterozoic, Paleoproterozoic, Paleozoic, Pennsylvanian, Permian, Paleogene, Paleocene, Pliocene, Pleistocene… makes for messy and confusing geologic maps. Also reminds me of emoticons with stuck-out tongues. ;P I know “Tertiary” is a Neptunist term, but “orogeny” is a geosynclinal term, and we haven’t given that up. And I’m still arguing because I know Callan is going to argue back.)

So long-live the Q!

(At least until we agree on whether the Anthropocene has started or not…)

[Edit: Andrew Alden has followed the Quaternary-vs-Neogene discussion far more closely than I have, and gives a lot more detailed information here: The Quaternary is Back in the Ring.]