Long story short - About 13,000 years ago during the Ice Age a large object from space hit the 2 mile thick North American Ice Sheet in the Great Lakes area. This caused instant mass melting of the ice sheet, which caused a world wide flood. This is known as the Younger Dryas Event, the explosion caused by this space rock covered North America, the top of South America, across the Atlantic to Europe, and the Middle East, the evidence of this event is the dispersal of nano diamonds formed by the explosion. The Carolina Craters along the Eastern Seaboard of the US are from this event, which also deep froze all those big animals they find frozen around the Artic Circle. Mankind had an advanced civilization at the time, with many cities along coastlines, and these are now underwater. Several of the major temple sites remain, because these were built on higher ground than the adjacent cities. Some of the surviving sites are Easter Island, Nazca, Ollantaytambo, Paratoari, Tassili n'Ajjer, and Giza. The story of Atlantis handed down to us from Plato puts the destruction of Atlantis into this exact timeframe. Coastlines and islands were inundated by a massive rise of seawater as the oceans rose with the addition of the ice sheet that vaporized into steam, which rained worldwide, along with unbelievable melt runoff that raged across continents and filled oceans. Ever heard of Noah's flood?
Check out Graham Hancock for an introduction to this cutting edge story of what actually happened, sunken city sites, and probably more lost treasure than you could even imagine. I think these submerged cities will be the next great treasure sites to be discovered and excavated. Cheers!!