Period· The columns of time

Stenian

1.2 Ga → 1 Ga

Narrow belts of crushed rock cross every continent: the mountains that welded Rodinia, and the first organism we can give a modern name.

What the evidence shows

Its collisions left belts of metamorphic rock so narrow that the period is named for them, from the Greek stenos, narrow. One of them ran from Labrador to Alabama, and its counterparts stand on every other continent: they are the seams of Rodinia, the supercontinent assembled between roughly 1.1 and 0.9 billion years ago, which will hold for some 150 million years before mantle plumes take it apart. In Arctic Canada, in rocks dated to 1.05 billion years, a tuft of branching filaments called Bangiomorpha is the oldest fossil that can be assigned to a group still alive today, the red algae. It does three things at once that no older fossil is known to do: it is multicellular, its cells are of more than one kind, and it reproduces sexually.

Bounds and conventions

The period's limits were fixed on the chart, not read in the rock; what is measured here belongs to the mountains, the Grenvillian collision falling between 1.09 and 0.98 billion years ago. Rodinia's shape is a reconstruction and not an observation: the fit of its blocks is inferred from palaeomagnetism and from matching mountain belts, and rival configurations remain in print. How high the belts stood is disputed as well, the latest synthesis of the Grenville reading them as a broad, hot orogen rather than a high plateau. Bangiomorpha's age was long given as 1.2 billion years and was brought down to 1.05 billion by dating the beds that bracket it.

Sources

1. Cohen, K. M., Finney, S. C., Gibbard, P. L., Fan, J.-X. (2013). The ICS International Chronostratigraphic Chart. Episodes 36(3), 199–204, mise à jour continue, voir Cohen et al. (2025), Episodes.
2. Li et al. (2008), Precambrian Research · Assembly, configuration, and break-up history of Rodinia: a synthesis
3. Indares (2025), Canadian Journal of Earth Sciences · The Grenville Province: revisiting the orogenic framework and integrating recent findings
4. Gibson et al. (2017), Geology · Precise age of Bangiomorpha pubescens dates the origin of eukaryotic photosynthesis
5. Loron et al. (2019), Nature · Early fungi from the Proterozoic era in Arctic Canada