Graham's arguments have strong merit - the presence of the myth of 'civilizing HERO coming from the water with a BOAT, teaching agriculture, infrastructure, civilization' in regions that are not known to have had any contact until modern age points to one of the below:

- There was a 'civilizing hero' or heroes that visited those totally disparate regions and this points to the presence of a localized, capable civilization that was able to travel the globe

- Or, the majority of the cultures of the age were much more capable than what we previously thought, being able to travel large distances and have exchanges in between them and therefore this myth was shared.

If the mythology was 'Divine being descending from the skies to teach things', that could be understandable. Because thats what many people could easily imagine, and what many cultures already had as a myth.

But the myth of a 'civilizing, normal, human hero that visits here and there and teaches agriculture, infrastructure in the same manner' is too uniform and ordinary that it would be legitimate. This is without the commonality of those heroes having the habit of carrying a small bag in most of those myths.

However, even more important is astroarchaeology or whatever they call it - in the absence of writing and lingua franca, sky is the only constant for all humans. And its normal for humans to try to record events and their dates using this only existing universal language - after all, there is no way that your wise men wouldnt know how to read the stars and their time-location analogies, right... Therefore if they recorded the date of a significant event using the position of the objects in the sky, surely not only your own tribe's wise men would know how to read it, but even the humans in the future. (they never thought we would invent something like writing and forget such traditions).

Based on that, indeed, a lot of the prehistoric monuments point to a certain date at the end of younger dryas, which these prehistoric cultures described as catastrophic, cataclysmic in their monuments in different parts of the world. Which also explains the differing flood mythologies that exist in totally isolated cultures.

Graham seems to be the pioneer here. And the conservatism of modern scientific establishment, which descends from its scholastic roots that shaped in the shadow of Christianity that always prefers to explain history in a linear, developing fashion, shows itself again.

Note that humanity losing its accumulated knowledge is not an extraordinary thing. It happened many times before regionally, even continentally. Even today, our knowledge takes a LOT of effort to keep in the form of scientists, educators working everywhere, every day to catalogue and maintain it - it is a globe-wide effort. Yet we could still lose a huge swath of that knowledge if we end up having a nuclear war or another global catastrophe that will kill vast amounts of people and destroy large amount of infrastructure, therefore disrupting this extensive system of keeping knowledge. In the earlier ages, it would be much easier. Just remember the Library of Alexandria. And that, when writing existed and records of some knowledge at Alexandria was already duplicated and kept elsewhere. Imagine an era in which there wasnt writing but the wise-men relayed knowledge from generation to generation or inside their group/clique by teaching it through oral means. Just a small plague, a war, a major famine would cripple such knowledge-keeping systems. So it is possible that humanity may have had more advanced cultures or even what we would call civilizations (minus writing, maybe even that) that were lost because they were too localized and one major catastrophe crippled them...