on earth有三种意思作“到底”或“究竟”；“当今”或“世界上”；“一点儿也不”。on the earth的意思是“在地球上”。例句：What on earth is it？这到底是什么东西？We live on the earth．我们生活在地球上。
earth双语例句
1.People used to think the earth was flat.
人们曾经认为地球是平的。
2.People used to believe the earth was flat.
人们一度认为地球是平的。
3.There were low banks of earth between the rice fields.
稻田之间有低矮的田埂。
4.Water covers a large proportion of the earth's surface.
水覆盖了地球表面的大部分。
5.A new satellite has been put into orbit around the earth.
一颗新的人造卫星被送上了环绕地球的轨道。