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Microsoft develops ultra durable glass plates that can store several TBs of data for 10000 years
(unlocked.microsoft.com)
This is a most excellent place for technology news and articles.
Backup wikipedia once a year to a crystal and then civilizations thousands of years from now can comb through it as they wish.
This.. well roughly. People here say muh file formats etc. But you're really going for the maximum lifetime, if its uncompressed text, it wouldn't be too hard to reverse engineer if future people figure out that there's data on there at all. The harder part may be extracting the data at all. We could also include instructions on how certain file formats can be read.
It's is is still a great long term archive storage, and more likely the data would be transfered to a better storage device within a few 100 years (if we're talking about archiving the present for future archologists that is)
How amazing would it be if we came across some tomb that was just filled with thousands of scrolls detailing the whole history of Rome and Greece and all those other empires from the BC years?