http://www.iciba.com/earth
地球（指宇宙组成部分时用Earth，指人类居住的星球时用the Earth）
Earth or the Earth is the planet on which we live. People usually say Earth when they are referring to the planet as part of the universe, and the Earth when they are talking about the planet as the place where we live.
The space shuttle Atlantis returned safely to earth today. “
亚特兰蒂斯”号航天飞机今天安全返回地球。
