All life on Earth - from microbes to elephants and us - is based on a single genetic model that requires the element phosphorus as one of its six essential components.
But now researchers have uncovered a bacterium that has five of those essential elements but has, in effect, replaced phosphorus with its look-alike but toxic cousin arsenic.
While "the discovery does not prove the existence of a "second genesis" on Earth," it "very much opens the door to that possibility." Since we don't actually know if the microbe replaced arsenic with phosphorus in its DNA structure always possessed arsenic instead of phosphorus, the possibility exists of a theorized "shadow biosphere" on Earth - that "life evolved from a different common ancestor than all that we've known so far."
We are witnessing (or discovering) history - even if in its most minute progression.