The absence of oxygen on other planets means that those planets lack an ozone shield to protect life forms against UVradiation.
其他行星上没有氧气，这意味着这些行星缺乏保护生命体免受紫外线辐射的臭氧层。
2
Complex life evolved on the Earth's surface, but not on Mars or other planets in the solar system because on those planets, early surface life was killed by UVradiation.
The absence of an oxygen atmosphere on Mars and other planets in our solar system means that these planets also lack an ozone shield that would protect surface-dwelling life from UVradiation.