It's not clear to me that we understand the conditions under which the earth was much hotter, or specifically what conditions resulted in cooler periods. There

It's not clear to me that we understand the conditions under which the earth was much hotter, or specifically what conditions resulted in cooler periods. There was a article a few days ago discussing the theory that one of the ice ages was caused by inter-planetary dust. This is an honest (and unpolitical) question: how much do we know about these past climate changes are what caused them?