The Bible includes a creation narrative of the universe in general and humanity in particular and a worldwide flood narrative. Are these accurate? That is usually interpreted as the question: are these the earliest accounts? Let’s see.
There are many ancient accounts of creation (see here and here) and flood (see here and here). These were written down at some point based on oral sources. So the earliest one written down does not necessarily mean that is the earliest oral source. How can we know what is the earliest one?
There are three approaches to finding the earliest account: (1) the degeneration approach, which says there was an original, accurate account that spawned other accounts that are degenerate accounts; (2) the elaboration approach, which says that there was an original, primitive account that spawned other accounts that are creative elaborations that produced more sophisticated accounts; or (3) the variation approach, which says that all the accounts are variations of one another, and that what happened is the account that best explains how all the other variations came to be.
I submit that (1) is the best approach because the best-preserved account, the Bible, passes the test of what an original account would have in order to explain the other accounts as degenerate in some way. For example, either some details of the biblical accounts of creation and flood are omitted (e.g., the names of the first man and those who survived the flood) or extraneous material is added (e.g., conflicts between the gods). The Bible is the theistic account closest to a naturalistic account.
A previous post related to this topic is here.