Era· The columns of time

Neoproterozoic

1 Ga → 539 Ma

In the Neoproterozoic, from 1 billion to 539 million years ago, ice reached the tropics more than once, a supercontinent broke apart and the first animals appeared.

Era of 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 apart during this era, and the break-up is implicated in what follows: it multiplies tropical coastlines, which accelerates silicate weathering, a reaction that consumes atmospheric carbon dioxide and locks it away as carbonate, producing glaciations severe enough for ice to reach the tropics. Animals appear against this background, possibly as sponges in reefs some 890 million years old, then with the Ediacara biota, between 575 and 539 million years, soft-bodied organisms with no earlier equivalent and, for the most part, no later one. Molecules preserved in some of them settle part of the question: Dickinsonia carries the sterols characteristic of animals, which makes it the oldest large animal attested.

Bounds and conventions

The younger limit is a golden spike and among the best defined on the chart; the older limit is the round figure of one billion years. Between them, the dating of the glaciations and of the first animals is under active revision, and the supposed sponges of 890 million years are the most contested: if those structures are not animal tissue, the oldest known animals lose more than three hundred million years.