How, why, where, who, etc. on earth Definition 1 of 2Pro Tip 1/3Expressing Surprise Use it when something is incredibly surprising or difficult to believe. Where on earth did you find that rare book? Pro Tip 2/3Highlighting Confusion Shows you're confused and seeking an explanation for something unusual. Why on earth would they cancel the event at the last minute? Pro Tip 3/3Emotional Emphasis Adds emotional weight to your question, showing strong feelings. How on earth could you say something so hurtful?