Era· The columns of time

Neoproterozoic

1 Ga → 539 Ma

Four hundred and sixty million years in which ice reaches the tropics more than once, a supercontinent breaks apart, and the first animals appear.

What the evidence shows

Rodinia assembles and then breaks up across this era, and the breakup is implicated in what follows: more coastline, more weathering, more carbon drawn from the air, and glaciations severe enough that ice reached the tropics. Animals appear against that background, possible sponges in reefs of about 890 million years, then the Ediacaran biota between 575 and 539 million, soft-bodied organisms unlike anything before and mostly unlike anything after. Fat molecules preserved inside some of them settle part of the question: Dickinsonia carries the sterols that mark an animal, which makes it the oldest large animal confirmed in the rock record. The era ends where the Cambrian begins, and Ediacara now reads as its prelude.

Bounds and conventions

Its end is a golden spike and one of the best defined boundaries on the chart; its beginning is the round one billion years. Between the two, the dating of the glaciations and of the first animals is actively revised, and the 890 million year sponges are the most contested of all: if those structures are not animal tissue, the oldest known animals lose more than three hundred million years.

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. Turner (2021), Nature · Possible poriferan body fossils in early Neoproterozoic microbial reefs
4. Bobrovskiy et al. (2018), Science · Ancient steroids establish the Ediacaran fossil Dickinsonia as one of the earliest animals