MIAMI _ On the long list of reasons why few scientists have dared plumb the mysteries of the Bahamas' famed blue holes, toxic swamp gas actually rates pretty low.
Hydrogen sulfide gas, a byproduct of bacteria and plant debris rotting for eons, gets trapped in a murky zone called the halocline where dense salt water mixes with fresh rain water floating above. In some submarine caverns, swimming through the foul layer leaves divers with burning skin, retching stomachs or worse. That says a lot about the daunting challenges below: utter blackness, uncharted and claustrophobic passages, walls that crumble into clouds of silt, shifting currents and extreme depths that demand exotic diving gear, elaborate safety systems and Zen cool.
For Kenny Broad, a University of Miami scientist who led a National Geographic Society-backed expedition that made 150 dives into blue holes on Abaco, Andros and other Bahamas islands, the rewards far exceeded the risks.
The team, composed of expert cave divers and researchers from UM, the National Museum of the Bahamas, Florida Museum of Natural History and other universities, emerged from the dark caverns with findings that could shed new light across fields from natural history to microbiology to climate change.
"These holes are a time capsule of evolutionary science," said Broad. "They're a modern-day window into what it was like millions of years ago."
Starved of light and oxygen that typically fuels decay, the blue holes have produced an array of stunningly preserved fossils, from brown bones of ancient native Lucayans to shells of long-extinct land tortoise and freshwater crocodiles once thought to live only in Cuba.
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