Has mankind's progress been linear? or have we repeatedly risen and fallen, the history lost to legend and then forgotten?
It is fun to ponder, but short of digging up such remnants we won't know.
The way to start a research project with regular people at the front of this....is to project a map with the water levels at 300 feet below what they are now, and include the anticipated landmass. My guess is that we’d find a thousand sites of interest within ten years around both North and South America alone. Folks can fan out and start to dig up spots around the coast of the US, and show evidence of life before Columbus and even the Indians.
This would also solve several mysteries over how Asians (and likely Europeans) came to America over 18,000 years ago. It might explain how tobacco was delivered and used in the mummification efforts in Egypt. And it might explain how the various pyramids (both in Mexico and Egypt), are identical in nature.
"In his house at R'lyeh, dead Cthulhu waits dreaming."