This was YouTube's decade. Plus: Top ten Web moments of the '00s

It seems inevitable and permanent now, as much a fixture in the American mind as McDonald's or Time magazine.

But YouTube, it is easy to forget, did not exist when the current decade opened.

It didn't exist in 2001 or 2002.

There was no YouTube in 2003 or 2004, either.

Not until "Me at the zoo," a video of co-founder Jawed Karim standing in front of elephants at the San Diego Zoo, was posted in April 2005, was there, really, a YouTube.

Yet despite being around for fewer than half of the past 10 years, the video-sharing service is the decade's most-influential popular-culture force on the Internet.

From Karim talking about the length of the elephants' trunks in the still-available 19-second clip, it has spearheaded the widespread availability of video on the Web, everything from golf's Masters tournament, live, to brand-new episodes of popular sitcoms such as "30 Rock" in the same week they aired on TV.

These developments, of course, threaten traditional and long-standing delivery systems.

YouTube became the clearinghouse for the short, shared, "viral" videos that were key to making Internet culture into mainstream culture, and started to play a role in politics, especially in the 2008 presidential campaign.

It developed as a kind of chaotic library, a go-to reference resource for people seeking video of musical artists, old cigarette commercials or the latest news sensation.

And it has championed the decade's DIY aesthetic: Skip the professionals, was YouTube's implicit message.

Shoot your own video. Upload it here, fast and easy.

And in the end, it doesn't matter so much if your backyard trampoline-stunt footage (ouch!) isn't great art; what matters is the validation it seems to get by being hosted on an external site.

With YouTube, if you wanted your friends to watch what you made, you didn't have to drag them into your living room and plug the camcorder into the TV.

You just sent them a link, and they watched it at the same Web site that also has professional material by TV stars. The site echoed similar revolutions happening in writing, as blogs came to prominence, and in photography, where people shared photos on sites including Flickr. But with YouTube, it was even more so, because the bar to getting videos shown in public had been higher.

Professional creators of content tried to fight YouTube for a while, policing their copyrights zealously and seeking takedowns whenever possible. But eventually, they decided they'd rather switch than fight. Deals were struck, and the providers who didn't form their own YouTube channels to show highlights (as CBS, for one, does) offered the equivalent of YouTube clips and much more on their own sites or on professional aggregators. But even as YouTube has become a ubiquitous brand, it hasn't yet proved that it can translate its traffic — it is ranked among the top five Web sites — into revenue. The site has struggled to integrate advertising in a manner that won't alienate customers.

Rival Hulu — a project of General Electric (NBC), News Corp. (Fox) and Disney (ABC) that might be termed a professional version of YouTube — has announced that it will, next year, begin charging its users.

But the battle of getting people to pay for content on the Web — or of getting content to pay for itself via ads — is a, and possibly the, question for the next decade.

Tribune reporters Mark Caro and Kevin Pang contributed to this report.