In the Radiolab podcast Space episode (2004) Ann Druyan mentioned that the contents of the Voyager Golden Record will last for 1 billion years before the contents of the Record becomes unreadable. This raises some questions:
How will the Golden Record outlast everything mankind has created? What are the special features of the Record to reduce its deterioration? How did the billion year lifespan come up?
I have read that the Record is electropated with U-238 for alien civilizations to date the age of the Record. However U-238 is radioactive with a half-life of 4.4ish billion years. Does this radioactive decay of the U-238 reduce the potential lifespan on the Record?
What actually causes the Record to decay into unreadability in the near vacuum and emptiness of space?
(note: I have read the answer to this question but it doesn't exactly address my question. I do take that it is related though :) )
NASA made the record from stable, inert materials, and placed it in the vacuum of space where erosion is not an issue. The record sits underneath an aluminium cover. The only sources of decay are cosmic radiation and the interplanetary/interstellar medium. Cosmic radiation takes a long, long time to create visible distortion (basically it affects an area one atom wide). The interplanetary and interstellar medium consist mostly of monoatomic gases at very low density. Again, one atom at a time takes a long time to make a noticeable dent.
The comment about U-238 surprised me as I'd never heard about it before, but it's correct. As in point 1, atomic decay products only affect one atom at a time. Parts of the record may transmute, but that doesn't really affect the profile of the grooves in the record. The amount of U-238 is tiny, and it decays very slowly, so it can only affect a small fraction of the atoms in the record.
I haven't been able to find a formal calculation for the record's lifespan. It seems likely the 'one billion' was an offhand remark.