Meaning of "earth" in Essential American English Dictionary

earth

noun us /ɜrθ/

B1 (also the Earth) the planet that we live on

[ no plural ] soil or ground:

a pile of earth
how, what, why, etc. on earth informal

used when you are extremely surprised, confused, or angry about something:

How on earth did this happen?
Why on earth didn’t you tell me before?

(Definition of “earth” from the Webster's Essential Mini Dictionary © Cambridge University Press)