原句为it was the farthest that scientists had been able to look into the past.

请问the farthest在句中是作look的宾语呢？还是作look into的宾语？若是后者，那这个the past在句中是作什么成分的呢？

参考段落：They were, by far, the largest and most distant objects that scientists had ever decteded: a strip of enourmous cosmic clouds some 15 billion light years from earth；But even more important, it was the farthest that scientists had been able to look into the past, for what they were seeing were the patterns and structures that existed 15 billion years ago.