Everything has changed in less than ten years. It used to be that the library was the place to go when you needed to learn something. A librarian would point you to the right book, depending on your age, how smart you appeared to be, and how much detail you needed.

But anyway, the point is that the old Internet was like the world centuries ago, before public libraries. Back then if you had a question, you'd ask the nearest smart person, who'd either answer you or ask someone smarter. It was the same online in the 1980s and early 1990s: you'd ask somebody you knew via e-mail or you'd ask your listserv group, or you'd go to a Usenet newsgroup and, in effect, ask anybody. Answers would come from all kinds of people, and you learned a lot�not just about the subject, but about how to evaluate so-called experts and their answers and their arguments. You also learned that you too were already an expert about something, even if it was a small or specialized or trivial thing. The old Internet was an exciting, life-changing experience for many people, like taking your mind to a gym.

Then along came the World Wide Web, invented in 1990 as a better way to share files between large scientific agencies on the Internet. A decade later, it seems like the whole world is there. Today the Web is a mix of the old Internet and the rest of society. The big institutions are there, like news networks, government institutions, schools, corporations, and so on. At the same time there are millions of personal sites and small circles of passionate experts on an unimaginable number of subjects.

Many ask-an-expert Web sites are rooted in the old Internet experience. Not only is it fun to get answers to your question, but it's really fun when someone asks you the right question. More than just fun: a good question, one you never thought to ask yourself, will push you to learn something new. In fact, good questions are essential to scientific progress. I believe that's one reason many scientific groups create this kind of site.

Usenet groups, on the old Internet, learned to compile lists of frequently asked questions (FAQ files) to save work for everyone, expert and newbie alike. Most of today's Web expert sites do the same. Truth be told, I think that FAQs are the most valuable parts of these sites. The reason is that the Web serves the general public, and the public generally has simple, basic questions about scientific matters. It's easier for everybody if the answers to these questions are in a FAQ.

"Ask A Geologist" sites seem like a good thing. If you think of the Web as a big fair, ask-the-expert sites are like a booth with someone waiting to talk with you. But the experience isn't fast. Many sites warn you to expect a wait of a week or more. The experience is more like writing a letter to someone. Commercial services are closer to the booth-at-the-fair situation, and if you're willing to pay a little bit, you can get a high-value response to a sophisticated question.

And never forget the good old library. If nothing else, you can get Web access there.