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Even CDs made by the same company in the same year and wrapped in identical packaging might have totally different lifespans. That's what Library of Congress researchers found when they tested twin copies of Paul Winter's Grammy-nominated 1987 album Earthbeat.

The two seemingly identical discs were exposed to extreme heat and humidity in an accelerated-aging machine. They cooked for about 500 hours at 175 degrees and in relative humidity of 70 percent—about what you'd expect on a sweltering July day in New York City, but not quite as humid as a rain forest. One of the CDs emerged relatively unscathed. The other was zapped of its musical data, completely destroyed by oxidation. You can see the ruined CD, which became almost totally transparent, on the right:
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Recordable CDs—the kind you can burn or rewrite—tend to have more complicated degradation issues than their professionally-recorded counterparts. That's partly because they're made from organic dyes that break down faster, France told me. And as far as different kinds of discs go, CDs tend to be more stable than DVDs, mostly just because DVDs hold more data, so there's more to lose.

But this kind of obsolescence has a way of creeping up on you. Even the researchers involved with CD preservation efforts at the Library of Congress say that academics started thinking about this kind of work later than they should have. "We really haven't focused as much on 20th-century media because you just think there are multiple copies of things. People just assumed it's more widely distributed."
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