The film team dragged the camera and hundreds of pounds of equipment through the jungle for three weeks. Four research divers from the northern German city of Kiel handled the tricky job of filming underwater. Diving in caves is already more dangerous and technically challenging than anywhere else. But with an 80-kilogram camera, lots of lights and constant changes in the diving depth, it becomes backbreaking work. For team leader Florian Huber, from the University of Kiel's Institute of Prehistoric and Protohistoric Archaeology, every minute is a worthwhile investment. "The documentation of these caves is fundamental research," Huber says. "It enables us to take stock of things before we can ask further questions about individual objects."
This sort of stocktaking seems urgently necessary, especially in the Mexican underwater caves, where halfway systematic exploration began only a few years ago. The Las Calaveras cenote, with its roughly 125 scattered skeletons, is only the tip of the iceberg. Scientists are still completely in the dark when it comes to what remains to be discovered in the many caves that haven't been explored yet. "Some 3,000 to 5,000 cenotes are known today, but there is an estimated total of up to 10,000," Huber says. "Only a tiny fraction of that has been explored so far."
The fact that the caves have already produced spectacular treasures, including some of the oldest human remains found in the Americans to date, suggests that archeologists will find more. In fact, the number of finds grows with almost each new cave that's explored.
Treasure Troves of Past Millennia
In prehistoric times, man was already burying the dead in the dark underworld. When sea levels rose dramatically after the last ice age, about 10,000 years ago, the water level in the caves, which are connected to the Atlantic, also rose. Skeletons, fire pits and tools from the Stone Age gradually became submerged. Later, the Mayans, who lived in the region from about 3,000 BC until 900 AD, threw ceramics and jewelry -- and people -- into the cenotes. Their remains survived the ages just as well as those of long-extinct animals, such as the giant ground sloth and the mastodon.
"Perhaps the cenotes contain the answer to the questions of when the first humans reached the Americas and how the continent was settled," says Huber. Water even preserves things that would have disappeared within a short time on dry land. In the Toh Ha cave system, for example, scientists stumbled upon both the 10,000-year-old bones of a boy and a fire pit roughly 8,500 years old. "It looked as if there had been a fire there just the day before yesterday," Huber says.
Exploring the caves is extremely cumbersome. Finding them in the middle of the jungle is difficult enough, but exploring them is considered one of the most challenging and dangerous jobs a diver can take on. Only their lamps keep them from being left in complete darkness and often have to squeeze through narrow openings. If they churn up too much sediment in the process, visibility in the otherwise crystal-clear water can suddenly drop to zero.
'Panic, and You're as Good as Dead'