About 1.8 billion years ago, before Cambrian Explosion and after photosynthesis started; Sea waters has the same stable and concentrated oxygen level, and yet no major evolution event happened during that time, just Eukaryotes floating around. Plus, Oxygen lvl alone cannot explain the rich diversity of Genus and species of C explosion. That’s why some geologists assumed that panspermia didn’t happen some time after Late Heavy Bombardment but only during late Precambrian. However, the lack of impact events during Pc - C transition means that assumption contradicts the astronomical model of Solar System formation. Whatever happened before or during Cambrian explosion, that didn’t happened for a billion years.
Can you suggest an encyclopedia about paleozoic marine lifeforms? I'm so interested in this underrated period but I can't find anything detailed enough.
