Genuine question: how would we tell/know if it was more than once?
Doesn't other life-2 floating around in the primordial soup look like food to life-1? Or wouldn't it be co-opted mitochondria style?
Doesn't other life-2 floating around in the primordial soup look like food to life-1? Or wouldn't it be co-opted mitochondria style?
From biochemical similarities, the chirality of certain sugars and amino acids, dna similarities, etc. the evidence for a single common ancestor of all life on Earth is fairly strong; however we don't really have evidence that there never were other lifes that simply were outcompeted at their very early stages.