on earth

1. 1.

   used with question words to convey surprise

   “what on earth are you doing?”

Questions about on earth

What does on earth mean?

on earth means "used with question words to convey surprise".

Is on earth a common word?

on earth is banded "Uncommon" — turns up in careful writing rather than conversation. The band comes from how often the word appears in a large corpus of everyday English, not from an editor's impression.