December 1. The Cenozoic begins

Giovanni Arduino

The most recent 66 million years of earth history is the Cenozoic Era. Cenozoic comes from “cene” for “new” or “recent” plus “zoic” for “life,” in comparison to the Paleozoic, ancient life, and Mesozoic, middle life. The big subdivisions of earth history, the eras, came into common use about the start of the 19th Century. The first scheme, devised by Italian scientist Giovanni Arduino in the 1750s, subdivided the rocks into Primary, Secondary, and Tertiary, coinciding more or less with the Precambrian, Paleozoic, and Mesozoic and later rocks. The fourth grand division following the numerical scheme, Quaternary, was added in 1830 to account for the very recent glacial deposits found in Europe.

As the terms Precambrian, Paleozoic, and Mesozoic came into use in the early 1800s, the Primary and Secondary names were abandoned, but Tertiary and Quaternary were retained as periods of the Cenozoic Era. It took a long time for geology to outgrow the early terminology – it wasn’t until 2004 that the Tertiary was officially abandoned by international agreement. And now, the Cenozoic is divided into three periods – the older Paleogene and the more recent Neogene, whose names mean “ancient things” and “new things,” respectively, plus the Quaternary, an anachronistic name still retained. The Quaternary includes the present day. Because the changes in nomenclature are so recent, I can guarantee that you’ll still find lots of references to the Tertiary, and I’ll probably use it too. I’ll talk a bit more about additional subdivisions of Cenozoic time tomorrow.

Because the Cenozoic is so recent, the past 66 million years, we have a relatively good handle on it in terms of events, life, evolution, and timing, so it makes sense to have closely defined subdivisions. And because we do know so much about it, it also makes it a little harder for me to decide on which 31 topics to cover this month. But we’ll manage.

I want to remind you again of the scale of our journey, and the fact that it’s not a proper scale. The entire Cenozoic, 66 million years, which we’ll cover this month, is less than 1.5% of all earth history. To do this at the correct scale, the entire Cenozoic would have to be squeezed into the last five days of December.

—Richard I. Gibson

Image of Arduino in public domain