February 1. The Cambrian begins.

The Proterozoic is done. We’ve started a new era, the Paleozoic, which means “ancient life” in Greek. It’s part of an eon, the Phanerozoic, that includes all the eras and all the time beginning with the Cambrian and continuing up to the present day. Phanerozoic means “visible life”, reflecting the former thought that there was no life before this time. We know now that there was earlier life, and some of it, like the Ediacarans, was certainly visible, but the name continues to be used. It works if you don’t worry too much about the literal Greek meaning.

The first subdivision of the Paleozoic is the Cambrian Period. Although there are older fossils, the Cambrian is the first time period when they are abundant, and this helped early geologists work out the sequence of rocks and the order in which they were laid down. A lot of that work was done in Great Britain.

Adam Sedgwick at the University of Cambridge is considered to be one of the founders of modern geology. He studied rocks in Wales, which was called Cambria by the Romans, from the Welsh name for their land, Cymru. In 1835, he gave the name Cambrian to the older series of rocks in the mountains of central Wales.

We’ll spend the month of February in the Cambrian.