State of the planet· The columns of time
Interglacial
660 Ma → 651 Ma
Nine million years of thaw between two global glaciations, and the shortest regime on the ribbon. It is drawn because leaving it out would make two Snowball episodes look like one.
What the evidence shows
Between the Sturtian, which ends at 660.98 million years, and the Marinoan, which begins somewhere after 654.5, lies a genuine non-glacial interval, drawn here as nine million years. Drawing it is not a detail: the difficulty in explaining a Snowball Earth is not getting the planet into one but getting it out, and the fact that it happened twice, with a thaw between, is what any explanation has to account for.
Bounds and conventions
Its older edge is firm, being the end of the Sturtian ice; its younger edge is the weakest boundary on this ribbon. The second glaciation begins somewhere after 654.5 million years, and the nearest thing to a date is a bed of volcanic ash just below the glacial debris, at 651.2 million give or take 3.3. An ash bed dates itself, not the ice above it.