This article is from the alt.usage.english FAQ, by Mark Israel email@example.com with numerous contributions by others.
The spelling "alright" is recorded from 1887. It was defended
by Fowler (in one of the Society for Pure English tracts, not in
MEU), on the analogy of "almighty" and "altogether", and on the
grounds that "The answers are alright" (= "The answers are O.K.") is
less ambiguous than "The answers are all right" (which could mean
"All the answers are right"). But it is still widely condemned.