I was surprised to read in an eminent journal that the most durable medium was vinyl 33rpm records (over 100yrs) as against pressed CD/DVD (30yrs) then CD/DVD burnt (5-15yrs)according to disc quality.

Prewar nitrate film is almost unrecoverable now but later cellulose is still ok, but tape suffers print through and needs to be stored carefully.

As for hard drives, memory cards and memory sticks, nobody knows as they are still too young to assess.

So all those people like me, who are digitising their photos better keep the originals cool and dark and dry because they may last longer than the digital copies. Ponder on that if you will and rdave13 idea of more digital methods of storage may be just as perishable than the current lot.

Carving in stone isn't permanent either, it all comes down to one of the laws of Thermodynamics I think, entropy, delta S, everything moves to a state of disorder, loses energy and goes back to basics, iron/steel rusts to ferric oxide and needs energy in a smelter to turn it back to iron metal again but starts rusting immediately. You can tidy up a room put everything in order then let a horde of kids in there and it's a mixture again.