The Blue Hole -- Marine life around one of the world's deepest sinkhole.

The Blue Hole in the Bahamas is one of the world's deepest sinkhole. It, and many others in the Bahamas, was formed around 15,000 years ago during the last Ice Age when sea levels were significantly lower than they are today. Ice ages cycle every 20,000 years or so. In other words, where we were scuba diving around the Blue Hole was above sea level 15,000 years ago instead of 80 feet below the surface today. That was when Chicago was under 100 feet of ice and glaciers covered the Great Lakes. Well, so much for man causing climate change. But the marine life around the Blue Hole is fabulous (as observed in this video) and with the Blue Hole's geologic history, it is one of my top 20 dive sites.