May have been three times even: in addition to the two Neoproterozoic "snowball earth" episodes they discuss here, there's also pretty decent evidence for an ev

May have been three times even: in addition to the two Neoproterozoic "snowball earth" episodes they discuss here, there's also pretty decent evidence for an even older (~2.2 Ga) Paleoproterozoic one [1] I've worked a little bit on things relevant to this, previously discussed at https://news.ycombinator.com/item?id=18798130 https://news.ycombinator.com/item?id=18798130 [1] https://www.pnas.org/content/102/32/11131.short https://www.pnas.org/content/102/32/11131.short