Taylor Swift surprised fans in Vancouver last night with an acoustic version of Alan Jackson's 'Where Were You (When the World Stopped Turning).' Fans screamed throughout the five-minute song -- captured in a video below -- and many were clearly moved by the 21-year-old's tribute to the victims of the 9/11 terrorist attacks.

A few minutes into the video, the amateur videographer indicates that fans didn't recognize the song. It's possible 'Where Were You' was not as big of a hit in Canada as it was in the United States, but the screaming would indicate more than a few fans were familiar with the power of Alan Jackson's song. Of course, anyone who's been to one of Swift's shows knows there's screaming from start to finish, so it's difficult to draw any conclusions.

For her part, Swift didn't stumble over any of the weighty lyrics and did her best to stay true to the somber performance Jackson put on at the 2001 CMA Awards. Swift was just 11-years-old when the Twin Towers fell, but like many country stars she has strong memories of that day and understands how it changed our nation.

Watch Taylor Swift Sing 'Where Were You (When the World Stopped Turning)'