10 points
No, since everything we know about the LUCA is from its descendants. Microorganisms without descendants wouldn’t leave behind any evidence of their existence.
8 points
Using genetics alone, sure. But maybe there’s fossil or geochemical evidence of early organisms not belonging to any of the three surviving domains—or maybe we could estimate it just from statistics.
4 points
Maybe but I don’t think fossil evidence has enough information to confirm something isn’t from the main branch of the tree of life.
1 point
