If you could take a cell from any organism—an alga, giant sequoia, condor, or your second cousin—and dive through its membrane into its clear liquid cytoplasm interior, you would find that all life as we know it shares the same building blocks. Familiar amino acids and proteins initiate and accelerate the same chemical reactions in precisely the same ways, regardless of the organism. And all known life uses liquid water as a foundation.
It is for these reasons that biologists believe that you, me, the flea, and the bonobo all descended from a single common ancestor: a microbe that lived some 3.5 billion to 3.8 billion years ago and (luckily for us) reproduced, eventually evolving into all of the living things we see, and don’t see, around us. Biologists call that ancestor, somewhat prosaically, the last universal common ancestor, or LUCA.
But what if, in the nearly 4.6 billion years ...
