The conjecture is that the oldest details of the creation stories have been transmitted orally from the time of the start of the last ice age.
My reason for thinking this is that the Noongar creation story tells of the sky and earth touching together at the very beginning so there was no space in between and it was very cold. Then, in summary, totem spirits confered and discussed at length about what to do after which the Ancestor spirit beings created what is now country. Each ancestor spirit performed one or more specific tasks including: raising the sky off of the land and the ocean, carving out the river valleys and establishing lakes, rivers and water sources, pushing up mountians, and then becoming the motivating incarnations which created and maintain all the living spieces as well as forming many specific locations.
There is all manner of extra detail in the story of which one of the most important to Australian indigenous peoples has been the explicitly mentioned and culturally assumed principle of looking after country: caring for the land and all the plants, creatures, and people who live on it. This is a core concept of Australian indigenous culture. It is equal to and not really separate from the absolute importance of moort (= family). Unfortunately most wadjela (= non-indigenous people living in, on, at, and near Noongar Boodja = country) simply do not understand this.
But what I am interested in here is the idea of a time when it was very cold and land appeared as the sky separated from the surface of the waters. This was the Nyidiny “Coldness” (NB “ny” is said like the “ni” in English “onion”.) I propose that this description of dry land appearing as the sky lifted away from the ocean surface at a time when it was very cold, sounds just how elders of nations living on regions of continental shelf would describe the distant past as their country became exposed by the retreat of the ocean as the last ice age came upon the world.
(Sahul: Greatest terrestrial extent of the Australasian continental shelf )
A very interesting question arises here: Just when did this knowledge arise and/or arrive in Australia?
NB: is it plausible that the very start of the Garden of Eden story indicates a similar “raising of the sky off the waters” to reveal a beautiful land? I believe it is.
There is little reason to doubt that the oldest suviving stories of just about every culture arose when all knowledge was passed from generation to generation through oral tradition, dance, artwork, and careful copying of behaviours. We can also accept that, apart from Australian first nations and some other indigenous peoples around the world, just about all other ancient origin stories have been affected by the stories of victorious clans who became the ruling classes of the neighbouring societies they conquered. I am implying that the Garden of Eden story and similar others have been overlayed with patriarchal rationalisations of the terrible inequalities which resulted from the accumulations and theft of moveable and portable wealth such as accrued to herders and settled farmers after the end of the last ice age.
In the case of indigenous Australian peoples, I am thinking that much of the continental shelf around Australia does not extend far out from the coast except the north where, as the Sahul link above shows there was a vast area stretching from the north west of Australia (the Kimberley) stretching northwards almost to Timor and across to New Guinea and including the whole of the current Gulf of Carpenteria.
(Sea level changes over the last 200,000 years)
There is evidence of human beings living on the Australian continent 65K years ago, which was an intermediate glacial maximum time before the colder, last glacial maximum (LGM), of about 20K years ago. Therefore it is reasonable to accept that people lived for thousands of years on continantal land that became exposed over a period of several thousand years leading up to the LGM. From the LGM to the present the graph shows that global sea level has been rising consistently and a fair bit faster than the sea level had previously fallen to the lowest level of between 120 to 130 metres below current sea level.