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Mysterious ‘Sailing Stones’ Explained

It might just be the world’s slowest game of Red Light, Green Light: Huge rocks in Death Valley National Park race across the mud flats—but only when nobody is looking. The sailing stones, as they’re called, mystified park visitors and scientists for decades. But one man believes he’s solved the puzzle.

The dry lakebed known as the Racetrack playa looks much like the rest of Death Valley—cracked and dry in the summer and frozen in winter. But nowhere else in the park will you find strange tracks trailing behind each big rock and boulder. It looks as though the stones have dragged themselves through the desert, or as though they have been dragged, by some great cosmic hand. 

All summer, the stones are still. Through autumn, they don’t budge. Then winter roars in and creeps out. By spring, the stones have moved again.

Natural and supernatural theories have abounded: Unsurprisingly, many attributed the rocks’ stealthy movements to aliens. Some said wind was the culprit; others ice; others rain; still others, mystical energy fields. Some people even steal rocks from the park, hoping to harness their magical powers. 

Scientists have set up experiments in the playa since the 1940s, trying to understand what makes the sailing stones sail. But all the results have been inconclusive, and despite frequent checks, nobody has ever been able to catch the rocks in motion.

It took a space researcher to crack the case. Planetary scientist Ralph Lorenz was working with NASA, setting up miniature weather stations in Death Valley, when he first became interested in the stones. (Conditions in the park are so severe that it’s often used as an experimental stand-in for Mars.) Although his original work was focused on summer in the desert, Lorenz realized his instruments would work just as well for monitoring the playa’s rocks in the winter. Lorenz and his team pored over images of the stones’ trails, looking for some clue.

One rock stood out. “We saw one instance where there was a rock trail and it looked like it hit another rock and bounced, but the trail didn't go all the way up to the other rock, like it was repelled somehow,” Lorenz told Smithsonian.com. “We thought if there was a collar of ice around the rock, then it might be easy to imagine why it might bounce.” 

The final breakthrough came not in the laboratory or even in the desert, but in the kitchen. Lorenz poured a little water in a plastic container, then dropped in a small rock and put the whole thing in the freezer. When he took it out, he had a rock half-sheathed in ice. That rock went into another dish, this one filled with water atop a layer of sand. He set the rock in the water, ice side up, and blew on it to give it a gentle push. The rock floated across the water, scraping a path through the sandy bottom as it went. Lorenz had found the answer. 

“Basically, a slab of ice forms around a rock, and the liquid level changes so that the rock gets floated out of the mud,” he said. “It’s a small floating ice sheet which happens to have a keel facing down that can dig a trail in the soft mud.” 

Lorenz published his findings in the American Journal of Physics in 2011. Once he knew what to look for, he was even able to catch the rocks in motion.

Not everybody is satisfied with the ice-raft explanation. Park visitors ask why it happens, but they don’t want to hear about science, park ranger Alan Van Valkenburg told Smithsonian.com. “People like a mystery—they like an unanswered question.”

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Animals
Where Do Birds Get Their Songs?
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iStock

Birds display some of the most impressive vocal abilities in the animal kingdom. They can be heard across great distances, mimic human speech, and even sing using distinct dialects and syntax. The most complex songs take some practice to learn, but as TED-Ed explains, the urge to sing is woven into songbirds' DNA.

Like humans, baby birds learn to communicate from their parents. Adult zebra finches will even speak in the equivalent of "baby talk" when teaching chicks their songs. After hearing the same expressions repeated so many times and trying them out firsthand, the offspring are able to use the same songs as adults.

But nurture isn't the only factor driving this behavior. Even when they grow up without any parents teaching them how to vocalize, birds will start singing on their own. These innate songs are less refined than the ones that are taught, but when they're passed down through multiple generations and shaped over time, they start to sound similar to the learned songs sung by other members of their species.

This suggests that the drive to sing as well as the specific structures of the songs themselves have been ingrained in the animals' genetic code by evolution. You can watch the full story from TED-Ed below, then head over here for a sample of the diverse songs produced by birds.

[h/t TED-Ed]

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Animals
Watch the First-Ever Footage of a Baby Dumbo Octopus
NOAA, Wikimedia Commons // Public Domain
NOAA, Wikimedia Commons // Public Domain

Dumbo octopuses are named for the elephant-ear-like fins they use to navigate the deep sea, but until recently, when and how they developed those floppy appendages were a mystery. Now, for the first time, researchers have caught a newborn Dumbo octopus on tape. As reported in the journal Current Biology, they discovered that the creatures are equipped with the fins from the moment they hatch.

Study co-author Tim Shank, a researcher at the Woods Hole Oceanographic Institution in Massachusetts, spotted the octopus in 2005. During a research expedition in the North Atlantic, one of the remotely operated vehicles he was working with collected several coral branches with something strange attached to them. It looked like a bunch of sandy-colored golf balls at first, but then he realized it was an egg sac.

He and his fellow researchers eventually classified the hatchling that emerged as a member of the genus Grimpoteuthis. In other words, it was a Dumbo octopus, though they couldn't determine the exact species. But you wouldn't need a biology degree to spot its resemblance to Disney's famous elephant, as you can see in the video below.

The octopus hatched with a set of functional fins that allowed it to swim around and hunt right away, and an MRI scan revealed fully-developed internal organs and a complex nervous system. As the researchers wrote in their study, Dumbo octopuses enter the world as "competent juveniles" ready to jump straight into adult life.

Grimpoteuthis spends its life in the deep ocean, which makes it difficult to study. Scientists hope the newly-reported findings will make it easier to identify Grimpoteuthis eggs and hatchlings for future research.

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