Thesurface feature has remaine

Thesurface feature has remained in popular culture since the image of the "Face on Mars" was known.

Whenthis photograph was taken in 1976,many took it to be the proof that alien life existed on Mars.

......

Somepeople thought the "Face on Mars" was the evidence that someone had landed on Mars and built the"face" to let us know that.

请教老师：

(1)since the image of...was known 为什么不呢？since the image of..."has been"known 呢？

(2)如何理解这里的两句话？proofthat...和evidencethat...是同位语从句吗？从逻辑上看，句子的意思很难理解？老师能解释一下吗？

谢谢老师。

1.since 从句通常意味着从过去的某个时间点开始，所以使用过去式。但当它有用时，它相对罕见。

2. 逻辑很清楚。把照片当成火星有外星生命的证据有什么难以理解的？