1.distributed free of charge to newspapers是修饰photographs的
distribute接的是双宾语,distribute sth.(直接宾语) to sth.（简介宾语）.photographs是直接宾语.
2.which做定语从句引导词,限定修饰Precambrian glaciation.同时which在从句中代替Precambrian glaciation做了believe的宾语,不能再使用it指代Precambrian glaciation.
举个例子
可以说：I like the T-shirt which my brother likes.
不能说：I like the T-shirt which my brother likes it.