Twenty thousand years ago you could have walked from India to Sri Lanka. The coastline sat far out beyond where it is today. The sea had not yet begun to rise. The outer line on this map is that old coast and the inner line is the one we know. Between them the sea rose about 120 metres in three great surges, around 12,000, 9,500 and 5,600 BC, which cut Sri Lanka off from the mainland, filled the Persian Gulf, and took Sundaland, a landmass the size of India off Southeast Asia, to leave thousands of islands, essentially Indonesia. India remembers it as the story of Manu, the Sumerians and the Hebrews wrote down their own versions, and in the Tamil south people spoke of a lost land called Kumari Kandam. Southeast Asia has more flood stories than anywhere on earth, and in those the water comes from the sea with no rain. The survivors climb to high ground and nobody boards a boat. Scholars filed all of this under myth for a century and a half, but I believe it was the memory of one real event. Episode 2 of The True Cradle, The World Before the Water, is set in the lands those stories remember (link in replies below).