50 years

or "up to 50 years", it's nonsense, like those blank CDs, supposedly "to last 100 years", as they claimed 10 years ago, when CDR was "the" thing. They're all dead now, with little use. But hey, they said "up to", didn't they?

In any case, give it a few years and there'll be something with 10 times more capacity available, also to last xxxx years, etc.