Science Bedtime Story

Journey into the Cave of Bones

By Jenny Marder

Illustrations by Rebecca Mock

Layout by Megan Crigger

Marina stood at the mouth of the Rising Star cave and looked inside. Outside, it was the rainy season in this grassland part of South Africa, home to jackals and porcupines and cobra snakes and thorn trees. She knew that deep inside the cave lay thousands of bones. Small bones and large bones, jawbones and ankle bones, finger bones and foot bones and skulls. The bones belonged to strange creatures that lived a long time ago, before there were humans. But to reach the bones, Marina and five other scientists had to make a long, dangerous journey underground. From deep inside the cave, they could begin to solve the mystery of these creatures.

Marina entered the cave. The sun shone in through a skylight. She walked down a path of loose gravel rocks and turned left into a narrow hallway. It was much darker now that the sun was gone. A headlamp attached to her helmet lit the ground ahead, casting shadows. She dropped to her belly and shimmied through a dusty tunnel. The tunnel was called Superman’s Crawl. That’s because most people only fit through with one arm stretched above their head and the other held tight against their body, like Superman flying. Marina was small enough that she could crawl through, but barely — her whole body filled the opening. Bats lived deep inside the cave, she knew, and she hoped they wouldn’t fly right smack into her.

She emerged, headlamp first, and found herself face to face with the first difficult climb: a three-story rock cliff shaped like a dragon’s back, with spikes sticking out along its spine. She grabbed a safety harness stored on a shelf of rock and pulled it on, clipped into a rope and scaled up the rock face, searching for footholds and handholds as she climbed. At the very top was a three-foot gap, a deep black hole that looked bottomless and dropped down to nowhere.

Here’s the thing about injuries in a cave like this. If Marina were to break an arm or a leg, a medical team would be required to live with her in the cave until it healed. She tried not to think about that. She was scared, but she took a breath and then leapt across the gap, like a superhero.

The toughest bit came at the end: a climb down a narrow crack with jaggedy bits of rock sticking out, like teeth. It was like climbing down the jaw of a supersized shark. One section was especially narrow, only 7 inches wide — that’s skinnier than a soccer ball. She turned her helmet sideways and wiggled her body through. On the ground again, she dangled her legs into the last hole. Her feet found a ladder, and she was in.

Inside it was dark, warm and musty-smelling. Tiny crystals sparkled across the walls, and stalactites hung from the ceiling like icicles. They looked beautiful, like melted wax. And scattered across the dirt floor were the bones. Marina took off her shoes, so she wouldn’t crush the fossils with her feet. She knelt down and began to work. Soon she heard a shout. It was Becca, dropping into the cave. Then came Hannah. Now there were three scientists working in the cave together.

For a month, Marina and five other scientists climbed in and out of the cave every day. Once inside, they used toothpicks and small paint brushes to remove dirt from the bones gently, grain by grain. Sometimes they talked and sometimes they worked quietly, focusing on their fossils. They had to be careful - really, really careful - not to damage them. Many of the bones crisscrossed each other underground. Like a game of Jenga, it was a struggle remove the top bone without disturbing the ones underneath. Getting one bone out safely often required digging out three or four other bones with it. They had favorite bones: Hannah’s favorite was a lower jaw. For Marina and Becca, it was a set of tiny hand bones.

While they worked underground, clouds formed outside the cave. Heavy rain soaked their camping and cooking tents. People at the campground braced against the wind, holding the tents down by the tentpoles, so they didn’t blow away. And when the scientists emerged later that day, back up the narrow crack and down the spines of the dragon’s back and back through the Superman Crawl, they would hear of the great storm that had passed through. But underground, it was quiet and calm, and they focused on their job.

Each fossil they tagged with a number and put in a plastic baggie. Then they wrapped the baggie in Bubble Wrap, placed the Bubble Wrap in a plastic container, and wrapped the plastic with more Bubble Wrap so it was protected on its trip to the surface.

Months later, in a lab not far away, scientists pieced together the bones. In a big room, teams of scientists worked on the bones they knew best. There was a foot group, a body group, a skull group, an arm and a leg group, a tooth group. As they worked, the creature slowly came into focus. It was a hominid — not quite human, but closely related, and like nothing they’d ever seen. They named it Naledi, which means star in the African language, Sesotho (Seh-soh-toh).

Naledi, they think, walked upright like humans, but climbed trees like monkeys. Its brain was the size of a small grapefruit; its fingers were long and curved. It had small teeth, apelike shoulders and feet just like ours, except with curved toes that helped it grip the trees for climbing.

Especially weird was how the bones got into the cave. If they had been dragged there by animals, the bones of those animals would be mixed in. If they had fallen into the hole by accident or been trapped there by a natural disaster, there would be clues of that in the cave. But there were no other animal bones and no signs of earthquake or avalanche. It’s likely they were put there on purpose by the Naledi — maybe as part of a burial ritual. But exactly why and how remains a mystery.

And there are still so many mysteries to solve. How long ago did this creature live? What did it look like? How did it behave? How closely related is it to us humans? What did it eat? What did it do? Was it smart? How smart?

Scientists will be chipping away at these questions for a long time. Which means children like you will grow up to be science detectives who are smart and curious and brave, who strap on headlamps and climb up cracks in caves to study ancient bones. And the questions — those really big questions that today’s scientists haven’t answered, well, maybe you’ll be the one that solves that mystery.

We hope you enjoyed the first in our science bedtime story series for ages 6 and up.
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A reconstruction of Homo naledi’s head by paleoartist John Gurche. Photo by Mark Thiessen/National Geographic.

Discussion Questions

The map and the photo of the reconstructed Naledi species are from the October issue National Geographic magazine.
Watch the NewsHour discussion on the subject here.