When does knowledge become obsolete? And I mean knowledge, not just information. Information obsolescence seems like an easier problem because the bits are smaller: at some point, old phone numbers are truly obsolete. Old email addresses returned by mailer daemons are obsolete.
But what about groups of information bits that, taken together, become technic? Many people still know how to use a rotary phone even though they have nearly disappeared over the past twenty years. Is that knowledge, then, obsolete? What if you come across a very old phone booth in a rural area, still connected, but with a rotary dial? Knowledge of the old style of dialing might save you a longer trip to the next hub of civilization.
A very obvious example of a technic that will never go out of style is the ability to start a fire without matches. Sure, most of us may never need to do this, but if we're caught without matches and need heat or cooked food to survive, the knowledge of Ways to Make Fire becomes a matter of life and death.
So, kids in youth organizations routinely learn how to start fires, but not how to dial old phones--but they may learn Morse code, a communication technology from a far earlier era. How do we decide what to keep and what to toss? Because it's clear we can't take it all with us.
I've been musing on this since a patron asked us to help him locate an old technique for removing the adrenal medulla from animals. Nowadays, you can buy lab rats pre-demedullated. Is the extraction technique used today the same as that referred to in studies from the turn of the twentieth century? Well, as it turns out, it's a bit hard to say. A standard protocol for removing the adrenal medulla is available in current lab manuals, so a lab manual from the late 1920s or 1930s should illustrate contemporary techniques.
Oh, right: most libraries get rid of old lab manuals when new ones come out. Why? Because a tech using an old protocol is likely to come up with a different result, and that could be dangerous. And in a medical library setting, anything that's potentially dangerous has got to go. Clinical handbooks. Drug reference guides. Old lab techniques.
But wait! our researcher says. I now need that information for some other purpose. I know it's outdated and shouldn't necessarily be used in a clinical setting, but I need to compare my results with previously published studies. You can trust me to use the information in a safe and appropriate manner.
Therein lies the weeding rub: where to stash the almost-up-to-date materials, away from the lazy or rushed hands of the resident who needs some book right now (who cares if the new one is checked out! the old one should do just as well!), until enough time has passed that we can all agree that the information contained therein is obsolete--though the knowledge imparted is not.
There probably is no good answer, so I'll stop my musings there. But it sure would be nice if we could place that call now, rather than trudge another 30 miles through the stacks to see if we can't use the book in the next little town over....