For most of the earth's history they havebeen the only form of life on our planet. As Earth-dwellers, we always cherish thehope that we will be visited by little green men and that we will be able tocommunicate with them. But this hope is always in the realms of science fiction.

　　22.For most of the earth's history they have been the only form of life on our planet.

　　在地球上发展的大部分进程中，细菌是地球上唯一的生命形式。

　　23.As Earth-dwellers, we always cherish the hope that we will be visited by littlegreen men and that we will be able to communicate with them.

　　作为地球上的居民，我们总存有这样的希望：小绿人来拜访我们，而我们可以和他们交流。

　　24.But this hope is always in the realms of science fiction.

　　但是，这种希望总是只在科幻小说中存在。