>>/2316/
I should've made it clear that regarding the stone masonry, the same technique (which is very distinct) can be found at Peru, Egypt, and even Easter Island (a wall there). So again, has little to do with the Egyptians, possible the "first Egyptians" which have probably little to do with them. 

Much of what is attributed to the known Egyptians is misattributed to them, and they've simple "inherited" much of that.

 >>/2317/
Well, there have been huge climatic changes happening roughly 12,000 years ago. Picture attached is the sea level rise alone.