on the earth/on earth都有在地球上，在地上的意思，
one earth 还有“究竟，到底”的含义，用于疑问词之后(Used as an intensifier after who, what, when, where, how)
用以加强语气，用在非正式文体中(intensifier used to emphasize surprise, shock, anger, disgust, etc.)
同义词"the hell; in the world"
why on earth?究竟为什么？
What on earth/the hell do you mean?你到底是什么意思？
what in the world are you thinking？你究竟在想什么
