The Best Original Score category was introduced in 1934 and since then has undergone a lot of changes. From 1941 to 1961 the category was split in two, honoring Dramatic and Comedy scores in one category and Musical Scores in another (except in 1957 when it was all one category). From 1962 to 1969 the category was split to honor original and adapted scores separately. From 1970 to 1979 the category was split into "Original Score" and "Song Score and Adaptation." It returned briefly to this from 1982 - 1984, but from 1980 - 1981 and 1985 - 1994, all scores were considered under the same category. It was split once again in 1995 to recognize Dramatic and Comedy scores seperately and then merged again by 1999.
This year's nominees:
James Horner, Avatar: This is the 8th nomination for Horner, who has one previous win (for Titanic). His Avatar score has received nominations from the Golden Globes and BAFTAs.
Alexandre Desplat, Fantastic Mr. Fox: The best movie composer working today (at least according to me). Desplat has two previous nominations and also has a nomination from the BAFTAs.
Marco Beltrami, Buck Sanders, Hurt Locker: This is the 2nd nomination for Beltrami and the 1st for Sanders. Their work on The Hurt Locker has received no other awards or nominations.
Hans Zimmer, Sherlock Holmes: This is the 8th nomination for Zimmer, who has won once for his Lion King score. He also received a nomination for the Critics Choice Award.
Michael Giacchino, Up: This is the 2nd nomination for Giacchino, who has also received Annie and BAFTA nominations and won the Golden Globe, Chicago Film Critics and Critics Choice awards for his work on Up.