What is next in this sequence: era, period, ...?

The next term in the sequence era, period, ... is epoch. These are successive levels in the geologic time scale, arranged from larger intervals to smaller ones: eon, era, period, epoch, and age.

An era may span tens to hundreds of millions of years, while a period is a smaller division within an era. An epoch divides a period further, usually covering hundreds of thousands to millions of years. For example, the Cenozoic Era contains the Quaternary Period, which includes the Holocene Epoch.

The word “epoch” is also used more broadly for any distinctive historical or cultural period, such as an epoch in science or politics. In geology, however, it has a precise hierarchical meaning. A common mix-up is placing “age” immediately after “period”; age is actually a still-smaller unit below epoch. The current officially recognized epoch is the Holocene, which began about 11,700 years ago, although the proposed Anthropocene remains a debated or unofficial term rather than a formally accepted epoch.