Era· The columns of time

Mesoproterozoic

1.6 Ga → 1 Ga

The Mesoproterozoic, from 1.6 to 1.0 billion years ago, sits at the centre of the boring billion, six hundred million years of unusually stable geochemical archives.

Era of six hundred million years characterised by the stability of its geochemical archives. It occupies the centre of the interval the literature designates as the boring billion.

What the evidence shows

Oxygen remains at a low and stable level, the carbon isotope curve is flat, and the supercontinent stays assembled for 600 million years. The stability concerns the rocks and not the organisms: the same interval sees the appearance of eukaryotes, of multicellularity and of sexual reproduction, and the first substantial diversification of complex life. Recent work identifies real variation in the trace elements formerly taken to be uniform, and one interpretation makes nutrient scarcity the selective pressure behind those innovations. The era does not lend itself to the narrative form the rest of the timeline follows, which is itself informative: any history of the planet must account for 600 million years in which its chemistry barely varies.

Bounds and conventions

The era is named for what appears to be absent from it, and the name has outlived the data that supported it. The apparent stasis may follow from the resolution of the record rather than from the state of the world, and on that answer these six hundred million years constitute either a pause in the history or a gap in our reading of it.