The “big news” from yesterday, about a new form of arsenic-based life found in Mono Lake, seems, from what I’ve read today, to have been a bit exaggerated.
The bacterium in question was taken from an arsenic-rich environment — one to which it had presumably adapted by developing a tolerance for the stuff — and then fed a steady diet of arsenic. Over time it swapped out some phosphorus for arsenic (and not without, apparently, some ill effects). It’s a good “proof of concept”, certainly, and a significant broadening of what we know to be possible, but hardly the “second genesis” we were hearing about yesterday.
Commenter JK was right to ask about adaptation.