Windows on the Past Today, these caves are still underwater. T e 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 right in. Others look like deep pits. Divers climb down cliff s to reach the entrance. Still others look like small, muddy puddles. Divers squeeze down through the muck until they find a cave entrance. T e water has preserved these caves. Many
look a lot like they looked before the water rose. Some even hold clues to life long ago. T e scientists look for these clues as they
explore the caves. Kunz follows closely. He squeezes between columns. His air bubbles bounce against the cave ceiling. T ey pop, making a loud cracking noise. He sees ghostly, white fish slipping into cracks in the rock. T ey don’t have eyes.
Deep Discoveries 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. It’s been extinct for thousands of years. Kunz wonders how it ended up here. T e scientists find signs of other cave
visitors. T ey spot broken clay pots. T ey’re scattered across the cave fl oor. T en they find more bones. T is time, they’re human. Maybe they’re the bones of an ancient person
who lived here 12,000 years ago. At that time, people climbed into the caves to find fresh water to drink. Some may have gotten hurt or lost inside the caves. It’s an eerie discovery.
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 just 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 an expert 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.
Cave Mapping One cave really excites him. It stretches at least 180 km (112 miles). T at makes it the biggest underwater cave yet explored. It’s also the 4th biggest cave system in the world. It has a lot of entrances, too. Divers have found more than 140 sinkholes leading to it. More than 7,000 more sinkholes dot the
peninsula. T at means there are lots of places for pollution to drip into the water. T at’s why maps of the caves are important. T ey show where to protect the land above. T at can help keep garbage, sewage, and other pollution out of the water. More needs to be done. Many caves here
have yet to be explored. T ere could be many others that have yet to be discovered. For explorers like Kunz and Meacham, that means there’s more adventure to come.
WORDWISE cenote: a deep natural pit, or sinkhole
dissolve: to reduce a solid to a liquid form
erode: to move rock from one place to another
weathering: the process in which rocks are broken into smaller pieces
14 NATIONAL GEOGRAPHIC EXPLORER
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