The University of Miami anthropology professor and researcher led a three-year expedition with a team of 15 scientist into these dangerous underwater caves off Abaco, Andros and five other Bahamian Islands.
It's his most ambitious journey yet and it is the cover story of National Geographic's August issue.
"It's like jumping into a time capsule," the 43-year-old exclaims. Dr. Broad, director of UM's Abess Center for Ecosystem Science and Policy says he can't put into words the exhilaration he felt during his exploration into a pristine world 270 feet beneath us.
He and his team of biologists, climatologists, geologists, astrobiologists, and paleontologists spent 2008-2010 making more than 150 dives that lasted up to six hours, into a dark cave filled with cloudy sheets of toxic hydrogen sulfide.
The blue holes proved to be a scientific trove. The toxic gas combined with the bacteria create a hostile environment that allows fossils to be nearly perfectly preserved.
"Because a weird chemistry goes on, it perfectly preserves fossils, human remains, and animal species we didn't know existed," Broad said.
Among their findings, tortoise shells and crocodile remains over 4,000 years old. He says UM scientists are analyzing these samples to understand why these crocodiles, never before seen in the Bahamas, have become extinct.
Broad's journey is also giving us a glimpse into the original inhabitants of the Bahamas, the Lucayan Indians. He and his team found skeletal remains and question if they were thrown into the underwater caves as a violent act, sacrificed, or fell in by accident.
One sample from 13,000 years ago shows a pattern of abrupt climate change that happened over 50 years.
"The mere fact that it's happened, we know it's possible it could happen," Broad said. He also wonders if humans are exacerbating climate change. These questions remain to be answered, but Dr. Broad is not done. He says they've only scratched the surface.
"There's a lot beneath our feet that helps us understand where we came from but it can also help us understand where we're going," he said.