谁能解释一下下面这个句子“as”的用法,as是引导一个同位语从句么?

谁能解释一下下面这个句子“as”的用法,as是引导一个同位语从句么?
We can't give answers to the question as the extent to which the sea and the coast affected human life in the past,what percentage of the population at any time lived within reach of the sea.
to which是引导一个定语从句么?the extent 是先行词?