That's the general assumption, even though there might be another stable "island" of fairly stable isotopes for higher-order elements than observed so far. But

That's the general assumption, even though there might be another stable "island" of fairly stable isotopes for higher-order elements than observed so far. But as I said, they'd need to be created first through nuclear fusion of lower elements, so their existence is obviously less likely, let alone life forms evolving on top of them.