The story of Noah's great flood probably came originally from the Babylonian city-state of Sumer. This area is low, basically a basin, and apparently one great flood came once and was written about. However, there is literally not enough water on Earth to flood the world all over; If the ice caps melted, all of the rain fell, and the springs all erupted, tere would be enough water to flood about half of the land mass, and there is obvious evidence that none of these as ever happened. However, all coastal areas definitely have had major floods, and major flood stories.
Occam's Razor is the fact that the simplest explanation is usually true, as all things tend towards the simplicity and chaos of entropy, even in social affairs, and the simplest explanation, in this case, is not that several hundred million gallons of water suddenly appeared on the planet for enough time to flood out every culture, then, mysteriously as it had come, disappeared after a time, but that these cultures, as you said earlier, communicated and absorbed each others' culture; Nearly every area is within the reach of a coastal community or Tartars.
The simplest explanation for the mysterious tall race, in turn, might be a simple matter of eastern invaders, but that China tells of them too, and that we have no evidence of such a culture's being indigenous to any region. Therefore, the simplest explanation is that their home sank into a fault that we know to exist, and know to be potentially dangerous.
At any rate, on the subject of ancient technology, it is not actually surprising that people 10 000 years ago had nearly as advanced technology as was possessed as of the middle ages, 1 000 years ago. We tend to think that technology is linear, and under that assumption, we would still have rocks being tossed at each others' heads as our most advanced "tools" 10 000 years ago, and we would be sea creatures just a few years before. The thing is that society has changed, generally for the better, in spite of things like the Tartar invasions, Crusades, other "Holy Wars," slavery, etc., so that aside from constant atrocity the overall
human condition has improved. Therefore, whereas by 1 000 years ago housing for the populace and diet had improved, technology had hardly advanced; However, the rate of technology doubles every few years, so that, in numeric terms, you can think of 10 000 years ago as being 1.0001 on a technological scale, with the formula being (tech)=(2^(years/3))n+1. Therefore, whereas technology would still be below 1.25 about a thousand years ago, it would now be somewhere in the thousands (this obviously being slightly inaccurate, but you get the point). 10 000 years ago, we had A-frames, and built Wonders (ahem
) with them, and a hundred years ago the best we had were calipers and compasses and slide rules, only slight advancements. However, we now have computers that literally double in power every single year, making it uneccesary even to use tools for measurement at all. Most of the advancement is in the last undred years, and it gets faster every year; However, though our starting point may be unaccounted for, there is seemingly little difference between 10 000 years ago and 5 000, and between 5 000 and 2 000, and between 2 000 and 1 000, and so forth, whereas we were building up to our current velocity all along, with increasing acceleration.