Prep 255 题中pushing的用法

clairexuan9

Scientists have dated sharp-edged flakes of stone found in the fine-grained sediments of a dry riverbed in the Afar region of Ethiopia to between 2.52 and 2.60 million years ago, pushing back by more than 150,000 years the earliest date when it is known that humans made stone tools.

请教各位，这个句子当中的 pushing到底是做 have dated的伴随状语，还是 million years ago的同位语从句？

还是说本身pushing back就有verb就是动词的含义，所以只能把它看做是修饰的have dated, 而一旦， 后面的词是名词形式，那么就会是定语从句修饰链接名词？

这里Ing一直都不是100%的明白，谢谢各位大牛！