its the name of luka's new epic poemI googled PSA and the first result is Prostate Specific Antigen (actually the second but the first one doesn't even make sense to me) - I don't really see how that is relevant here.
Our ultimate relative was a single-cell, bacterium-like organism known as Last Universal Common Ancestor or Luca
The organism appears to have lived in vents deep in the sea, where metallic, gassy plumes erupt from seawater that interacts with magma that comes up from the ocean floor.