This is hierarchical organization, none of which is seen in the Precambrian layers beneath.
Far from being humble, primitive steppingstones to higher life, microbes display superpowers that so-called “higher” forms of life depend on.
“Convergent evolution” is not a process. It is a post-hoc observation based on evolutionary assumptions.
When it comes to causation, there are only two classes of causal forces; those are material causes and intelligent causes.
This is a case of evolutionary biology trying to explain away the data that otherwise was not directly expected under their model.