Possible Clues:

• See 40-Down
• Soil shortage duke ignored
• __ tone
• See it in space and in the dirt
• 'Ome with this primitive floor?
• Planet invaded in 'The War of the Worlds'
• The so-called "blue marble"
• First husband leaves home for underground shelter
• Martians' target, in much sci-fi
• Connect for safety in 13