Windows on the Past Today, water still fills these caves. T e only way to explore them is to wear diving gear. And the only way to get into them is through a cenote. T ese sinkholes form when cave roofs
collapse. Some sinkholes look like shallow pools. Divers can walk in. Others look like deep pits. Divers climb down cliff s to reach the opening. Still others look like small, muddy puddles. Divers squeeze through the muck to find the cave. T e water has preserved these caves. Many
look like they looked before the water rose. Some even hold clues to life long ago.
Deep Discoveries T e scientists look for clues as they explore the caves. Kunz follows closely. He squeezes between columns. He sees pale white fish slipping into cracks in the rock. T ey don’t have eyes. His air bubbles bounce against the cave ceiling. As they pop, they make a loud cracking noise. He hopes his bubbles don’t stir up any blinding dirt. Suddenly, a team member’s light shines on
an odd shape. It’s not a cave formation. It’s a pile of animal bones. T ey came from a giant ground sloth. T is animal has been extinct for thousands of years. Kunz wonders how it ended up in a cave. Soon, the scientists find signs of other cave
visitors. T ey spot broken clay pots. T e pieces are scattered across the cave floor. T en they find more bones. T is time,
they’re human. T e bones came from people who lived
in the area 12,000 years ago. T ese ancient people likely climbed into the caves to find fresh water to drink. Some of them may have gotten hurt or lost inside the caves. T is eerie discovery is a clue to the past.
14 NATIONAL GEOGRAPHIC EXTREME EXPLORER
Key to the Future T ese caves also are important for people today. Like the ancient people, they depend on the caves for fresh water. So it’s important to prevent pollution here. Yet it’s hard to protect something you don’t
understand. No one knows how far these caves stretch under the jungle. No one knows how the caves connect. Sam Meacham is trying to find out. T is
National Geographic Explorer is a cave diver. He and his team are making maps of the caves. As Meacham dives, he plots each cave’s twists and turns. He takes videos. He makes notes in a waterproof notebook. One cave really excites him. It stretches at
least 180 km. It’s the longest underwater cave system yet explored. It also may be the fourth biggest cave system in the world. More than 140 sinkholes lead to this long
cave. T at’s just a fraction of the more than 7,000 sinkholes that dot the peninsula. So there are lots of places for pollution to seep into the water. Once it gets into the cave system, it can flow from cave to cave to cave.
More to Explore T e cave maps can help prevent pollution. If people know where the openings to the caves are, they can protect the land above the caves. T at can help keep garbage, sewage, and other pollution out of the water. If people know how the caves connect, they can see where pollution might spread. More needs to be done, though. Many
caves here have yet to be explored. T ere could be many other caves that have yet to be discovered. For explorers like Kunz and Meacham,
that means there’s more adventure to come. “It’s thrilling,” says Meacham. “T is is some of the last exploration leſt on Earth.”
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