"There Will Be Blood" features a score that sounds like it could have been heard in the period, 1898 - 1927 (with the bulk of it taking place in 1911, the year Arnold Schoenberg published "Harmonielehre"). Some of it was composed in 2005-06 (Greenwood); some in 1878-79 (Brahms).
From Daily Variety (1/21/08):
Jonny Greenwood's original score for "There Will Be Blood" has been ruled ineligible by the music branch of the Academy of Motion Picture Arts and Sciences. [...]
The disqualification has been attributed to a designation within Rule 16 of the Academy's Special Rules for Music Awards (5d under "Eligibility"), which excludes "scores diluted by the use of tracked themes or other pre-existing music."
[Radiohead lead guitarist] Greenwood's score contains roughly 35 minutes of original recordings and roughly 46 minutes of pre-existing work (including selections from the works of Arvo Pärt, as well as pieces in the public domain, such as Johannes Brahms' "[Violin] Concerto in D Major"). Peripheral augmentation to the score included sporadic but minimal useage (15 minutes) of the artist's 2006 composition "Popcorn Superhet Receiver."
What's peculiar is that the Oscar nominations are due to be announced Tuesday the 22nd, and the Academy didn't announce it's disqualification ruling until Monday the 21st. So not only was it too late for the filmmakers to appeal, but members of the music branch who voted for Greenwood's score were unable to vote for something else instead.
The ruling is perfectly valid and consistent. The timing is inexcusable. AMPAS continues to screw up royally, even according to its own rules.