It ought to be:
Like marrow from a white bone, his soul could be drawn from him at any time by the Martian air.
Since “Martian” describes the air of Mars, it is a proper noun and will have the article “the” before it.
It ought to be:
Like marrow from a white bone, his soul could be drawn from him at any time by the Martian air.
Since “Martian” describes the air of Mars, it is a proper noun and will have the article “the” before it.