The antediluvian world

Although various ancient traditions refer to a lost antediluvian world, the one that stands out is the tradition in the early chapters of Genesis, because of its geographical detail, its monotheism (which has been shown to predate polytheism) and its historical (rather than epic) style of narration. These chapters describe a world very different from our own, either because the world really was different or because a later pre-scientific culture speculated about it in error. So what source of information did they draw upon?