The recent NOVA episode on extreme cave diving in the “blue holes” of the Bahamas struck me as almost over-the-top extreme:
Including the expedition leader, anthropologist Kenny Broad, the dive team has recovered the bodies of more than 100 cave divers. To imagine recovering just one, think of a flooded, crumbling 10-story building at night. There’s a dead body in the basement. You have to find it and drag it to the roof. Could you? What if it was a friend? Wes Skiles recovered the body of his best friend from a cave. He also recovered three brothers who realized they were hopelessly lost and out of air. Wes found them holding hands.
Not far into the episode, they find a human arm bone, then a flashlight, and then more remains in a 1970s-era wet suit. They also found some older remains:
At their deepest level, blue holes are anoxic, and this lack of oxygen helps to preserve whatever falls in. Our team was able to recover two skulls belonging to ancient humans, the fossils of vertebrates that are now extinct in the Bahamas, and fossils of birds that aren’t just extinct but have never before been described by science. Living within the blue holes are at least one new order of multi-cellular creatures, descended from animals that evolved millions of years ago, as well as single-celled organisms virtually indistinguishable from the first life-forms on Earth. Parts of blue holes are like our planet’s first seas, from a time four billion years ago when the Earth had no oxygen. NASA was interested in the expedition because the extreme life-forms found in blue holes are similar to what they hope to find on other planets.