State of the planet· The columns of time

Interglacial

660 Ma → 651 Ma

Between 660 and 651 million years ago, nine million years without global ice separated the two snowball glaciations of the Cryogenian, the shortest regime in the series.

Non-glacial interval of nine million years separating the two global glaciations of the Cryogenian, and the shortest regime in the series.

What the evidence shows

Between the Sturtian, which ends at 660.98 million years, and the Marinoan, which begins after 654.5, lies a non-glacial interval that the band represents across nine million years. Depicting it is not incidental: the difficulty posed by the snowball hypothesis is not entering that state but leaving it, and the fact that this occurred twice, with a thaw between, constitutes the principal constraint on any explanation.

Bounds and conventions

Its older limit is firm, corresponding to the end of the Sturtian ice; its younger limit is the most weakly constrained in the series. The second glaciation begins after 654.5 million years, and the closest approximation to a date is a volcanic ash bed immediately beneath the glacial debris, dated to 651.2 million years to within 3.3. An ash bed dates its own emplacement and not the ice above it.