English Idiom of the Day – Where on Earth
Adding 'on earth' is an idiomatic way of intensifying the word 'where'. For example, 'Where are my keys?' is a simple request for information. But 'Where on earth are my keys' implies that the person is frustrated and has been unable to find their keys and wonders where in the whole world they could be.
Example: Where on earth did you get that ridiculous hat? Where on earth are my keys?
Similar expressions: 'What on earth...?', 'Where in the world....?', 'Why on earth...?', 'How on earth...?' . The words 'on earth' or 'in the world' can be added to what, where, who, why or how to add emphasis.