Savages : Classical piece used in the film

Anyone know the name of the classical music used in Savages that is a single soprano singing a haunting melody? I have heard it in another film years ago, but I can't recall which. I would really like to know the name of that piece!

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Of course, as soon as I post this, I manage to run across the piece randomly.

For the record, it's John Tavener's Eternity's Sunrise...

...and the previous film was Children of Men!