> So does this imply that we'll never know if the Cambrian Explosion is actually an explosion or just a continuation from a previously unrecoverable geological

> So does this imply that we'll never know if the Cambrian Explosion is actually an explosion or just a continuation from a previously unrecoverable geological record? Is it even possible to have complex multicellular life under snowball earth conditions? That's a good question. I'm the first author of the new PNAS article discussed here (open access at https://doi.org/10.1073/pnas.1804350116 https://doi.org/10.1073/pnas.1804350116). This does raise some questions about preservation bias and taphonomy, but there are areas we know escaped Neoproterozoic erosion (mostly at actively rifting continental margins) and we can find continuous sedimentary sections from the Cryogenian to the Cambrian -- and in these sections we still see a pretty rapid rise in complex shelly fossils in the early Cambrian. That said, when people first started talking about the "Cambrian Explosion", we didn't know much anything about the Ediacaran biota [1], the Ediacaran extension of the "Small Shelly Fauna" [2], or the Doushantuo Formation [3] -- so the evolutionary problem's not quite as bad as when Darwin first worried about it. One new point to add is that erosion and comminution of this much crust may be expected to free up a lot of phosphorus stored in the igneous crust -- arguably the key limiting nutrient on geological timescales. This seems to be be consistent with previous observations of an increase in phosphorus abundance in sediments around Cryogenian times [4]. [1] https://en.wikipedia.org/wiki/Ediacaran_biota https://en.wikipedia.org/wiki/Ediacaran_biota [2] https://en.wikipedia.org/wiki/Small_shelly_fauna https://en.wikipedia.org/wiki/Small_shelly_fauna [3] https://en.wikipedia.org/wiki/Doushantuo_Formation https://en.wikipedia.org/wiki/Doushantuo_Formation [4] https://www.nature.com/articles/nature20772 https://www.nature.com/articles/nature20772