There are two related problems here.
The first is the survival of the media itself; in other words,
how long will the information remain on the medium and/or will the
medium be accessible in a practical way? As I understand it, CD's,
and especially CD-R(W)'s have finite lifespans, as do most if not
all forms of magnetic tape (probably including computer drives as
well); further, magnetic media is easily rendered unreadable by
exposure to magnetic fields. In fact, we should no longer use
"carved in stone" as a cliche denoting permanence, since any
number of 19th century tombstones are completely illegible!
The second is the survival of whatever might be necessary to read
the information...this can be anything from humans conversant
with the language used (which is, for example, why we get no
useful information from Etruscan inscriptions!) to various
devices of ever-increasing levels of precision and complexity
required to access modern media. As near as I know, there are
no examples of media for which no reading devices survive I could
be wrong)...but there are many for which no devices are currently
being built (Regina perforated discs, wax cylinders, wire recorders,
8-track (or worse yet, obscure 4-track) tape cartridges, usw.)
It is not impossible that someday the last surviving player/
reader for any or all of these will fail in some non-repairable
way, leaving a certain amount of information no longer accessible.
Given the ever-decreasing lifespans of technologies, there is no
guarantee our successors...or even ourselves in our dotage...will
be able to access the data we carefully preserve for them!
In fact, I have 60-odd MB of data on an old RLL hard drive, and
the only practical way of accessing it is using an old enough
computer...and the data is just over 10 years old!
There is also one rather esoteric third consideration: considering
that the eventual finders either may be non-terrestrials, or be
from a much-advanced (or much-degraded?) future technological
setting, will they even be able to recognize that something
contains information at all? Careful scrutiny (or even accidental
"tracking" of a groove) of a 78rpm record will reveal it contains
some sort of data...can the same be said of a CD (which will
probably be a long-discarded AOL offer in any case)?...
Steven C. Barr