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According to scientists, the archipelago of 700 islands and 2,400 islets & cays that constitute The Bahamas, are very unique. Unlike other land formations, these were formed entirely in shallow waters from layers of sediment that compressed atop each other and, gradually converted into limestone.
When sea levels were lower, water from the rain eroded the limestone rocks, turning them into huge underwater cave systems. Known as 'Blue Holes', because of the contrast between the deep dark waters in the middle and the light blue color on the sides, they are not only amazingly beautiful, but also, contain a treasure trove of information about extinct animals and past civilizations.
However, while existence of the caves has been known since 1725, it is only recently, that divers have been daring enough to explore this mysterious underworld. That's because while they may look like innocent swimming holes, they are extremely perilous and divers entering them have to be ready for the worst.
While the top layer of the water, which comprises of fresh water looks refreshingly inviting, beneath it lies heavier saltwater, that is often covered with clouds of poisonous hydrogen sulphide gas, released by salt-eating microbes. If exposed to for too long, this gas can penetrate through the wetsuit and skin, and result in nausea, disorientation and even, death. If that is not enough, some Blue Holes contain whirlpools instigated by the powerful underlying tides.
Once the divers get through these hurdles, they are faced with vast, pitch-black, maze-like caves that can be as deep as 600ft, and extend for miles on end, in all directions. It is therefore not surprising, that only the most trained divers can attempt to explore the holes, and even they are tied to safety lines, so that they can be pulled up should something go wrong.
All divers carry three tanks of a breathing gas mixture of Nitrogen and Oxygen - One for going in, another for coming out and the third, for emergencies. They also carry three lights, which not only help them see in the dark waters, but also, navigate. Should any of the lights fail, the divers are trained to call off the dive and return to the surface.
However, once inside, the caves are not only amazing to look at, but also, provide a wealth of information. Inside the 20 caves that have been explored so far, divers have discovered perfectly preserved remains of extinct crocodiles and turtles, fossils belonging to the Lucayan tribe who inhabited the islands in the 1500's, as well as, amazing stalactites, which store data on climatic conditions that existed in past eras. Not only that, they have also discovered bacteria that have learned to survive without oxygen by adapting to whatever is available in the caves.
The best part is, that there are still thousands of blue holes waiting to be explored - Not just in the Bahamas but also off the coast of Belize, Australia and even, the Red Sea. We wonder what kind of treasures they will reveal.