I agree with Jerry that archives aren't generally in the business of
preserving their contents against every possible contingency, such as
nuclear war or other civilization destroying events. We plan the for the
future as practically as we can. That's hard enough.
Mechanical and digital storage have their advantages and
disadvantages. Both need to be "migrated" regularly to preserve access
and data integrity (shellac discs may be the longest lasting medium we
know of so far, but they're still not permanent). But digital
preservation files have the distinct advantage of being able to be
monitored and re-preserved (converted to new file formats and/or moved
around storage locations) automatically with little or no loss of data.
Of course the means to monitor and migrate data must be part of any
serious digital preservation plan, but this seems to widely recognized
now. 20 year-old computers and their data are difficult to salvage
because migration plans did not exist.
Several years ago at LC, I saw someone from the Church of
Scientology demonstrate their long-term preservation medium for L. Ron
Hubbard's lectures. It was a conventional disc made of some special of
non-oxidizing alloy, vacuum-sealed in a special sleeve. The person
claimed that these discs should last for thousands of years, and if I
recall correctly, the disc format was chosen specifically because of the
ease of retrieval by other civilizations, domestic or alien. As far as I
know this is the only example of an archive seriously looking to a
post-"civilization" era and acting on a solution.
Conjecture about preserving data for archaeologists or alien visitors
amusing but not very applicable. Any archival media should be
every "few" years to detect any degradation and to allow a copy to be
made if any risk is detected. Transfer to media using updated
should be anticipated every 20 years or so.
Material that is centuries, or even decades, old can be expected to be
severely degraded, as is now being discovered with film. Material that
is thousands of years old usually contains very limited information,
digitally equivalent to a few bytes, not GB, and its limited visual
content must be painstakingly reconstructed.
In context, information can be carved into granite, cast into
or whatever you like. Such efforts can only preserve very limited
amounts of information (cave drawings anyone), and lingual or pictoral
content would probably be just as difficult to interpret eons hence as
coded digital data would be.
Media Sciences, Inc.