Thanks to Skillshare for sponsoring this episode — and this whole week! — of SciShow. [ INTRO ].

To the frustration of scientists everywhere, things in this world sometimes just don't make any sense. But for the rest of us, that can be kind of amazing.

Imagining what could cause unexplained phenomena — like weird lights in the sky, or sightings of mythical creatures — can be a lot of fun. Just ask half the forums on the Internet. But it's also good to remember that the world doesn't have to be shrouded in mystery for it to be fascinating.

Exploration can be just as cool as speculation. So to that end, here are six mysteries — from the Easter Island statues to will-o'-the-wisps — that scientists have managed to solve. We've talked about all kinds of weird weather here on SciShow, but this might be one of the best and most horrifying stories yet.

Imagine it's March 1876, and you're living in Bath County, Kentucky. You're outside on a beautiful, perfectly clear spring day when the unthinkable happens:. It starts to rain chunks of meat.

Some of them are small — about 5 by 5 centimeters — but others are as big as your hand. And soon, your yard is covered in the stuff. I wish I could say this wasn't a true story, but yeah, this 19th-century version of “Cloudy with a Chance of Meatballs” actually happened.

According to the New York Times, two guys even tasted the meat rain — because they just had to be curious — and decided it was either mutton or venison. This event came to be called the Kentucky Meat Shower, and it baffled people for decades. Originally, one person thought the culprit was something called nostoc — which we now know is a kind of bacteria covered in a jelly-like membrane.

And when it rains, that membrane swells up. Except, it wasn't raining when the meat shower happened, so that idea was tossed out the window. Eventually, though, scientists did figure it out after studying some preserved samples.

They found that the meat was meat — specifically, a mixture of animal lung tissue, muscle, and cartilage. And later in 1876, the chemistry professor L. D.

Kastenbine discovered where it came from: synchronized, projectile vomiting vultures. This story is amazing. There are two species of vulture native of Kentucky, and their eating habits totally explained the shower.

For one, vultures aren't picky eaters, which is why there were various kinds of tissue, and why the meat pieces were all different sizes. But more importantly, vultures are also frequent vomiters. Vultures are known to eat huge meals, and if they're disturbed before they have time to digest all that food, they sometimes throw it up to make themselves lighter and make escape easier.

So Kastenbine concluded that, on that day in Kentucky, a group of vultures just happened to be flying overhead, and all puked at the same time. It's possible that this has even happened in other places, too, but cases haven't been well-documented. Either way, yeah, it's a little gross.

But it's the Kentucky Meat Shower, there was never going to be a not gross explanation. Easter Island in the southeast Pacific is famous for its giant statues. They're called moai, and they were built at least 400 years ago by the Rapa Nui people of Polynesia.

But here's a lesser-known fact: Those statues used to have little, reddish hats. Okay, maybe “little” is an understatement. The hats were about two meters across and weighed up to 12 metric tons.

And until 2018, it was pretty unclear how the Rapa Nui managed to put them on the statues. After all, the moai are some 10 meters tall, and the hats were really heavy. Also, it was hundreds of years ago.

Cranes were a little on the scarce side. But using modeling, a team finally figured it out. In a 2018 paper published in the Journal of Archeological Science, researchers discovered that the Rapa Nui likely used a technique called parbuckling.

First, they would have carved the stones into cylinders. This red rock is actually found on the other side of Easter Island, so making a cylinder out of it allowed them to roll it over to where the moai were. Then, they built a ramp leading up to a statue's head.

They tied a rope around the cylinder, and then a team of probably 15 people hauled it up the ramp and put it on top of the statue. After that, the hat was carved into its final shape. It sounds like figuring that out would have been easy, since it's all based on simple machines you might have learned about in elementary school.

But discovering this required building 3D models of about 50 statues and 13 cylinders, as well as making all kinds of calculations about the weight of the rocks and the strength of the average ancient Polynesian. Today, you probably won't see many of these hats still on their moai, since weather and erosion have knocked most of them off. But at least they're no longer a mystery.

Scientists can't tell us how to predict an earthquake, since there are so many variables to keep track of. But they can tell why before and during ‘quakes, people have sometimes reported seeing mysterious lights in the sky. They're called earthquake lights, and they can take all kinds of forms, from blue flames to lightning that shoots out of the ground.

People have recorded seeing them as far back as the 1600s, and they've been observed up to weeks before major earthquakes and up to 160 kilometers from the epicenter. Unsurprisingly, some people blamed these lights on UFOs. Others thought they were caused by disruptions in the Earth's magnetic field.

But the real answer came in 2014, in a paper published in Seismological Research Letters. In it, the authors investigated data from 65 earthquakes where people had reported seeing lights. And they found that, most likely, the culprit was electrical activity in certain types of rocks, especially volcanic ones.

The team discovered that, when you put a lot of stress on these rocks, they can release electric charge. The pressure causes the chemical bonds between certain compounds in the rocks to break, which releases charged oxygen atoms. If enough bonds are broken at once — like before or during a big earthquake — a bunch of those charged atoms can rush up to the surface, usually at a fault, where two sheets of rock meet.

Then, when they burst above-ground, they can ionize the air, giving /air molecules/ electric charge. And that ultimately creates the various flashes of light. The conditions that cause these are pretty specific, which explains why earthquake lights are only seen in about 0.5% of earthquakes.

And the team also mentioned that this phenomenon can explain other things detected before quakes, like low-frequency radio emissions. Unfortunately, understanding earthquake lights probably won't help us predict ‘quakes, since they're so rare and since people usually don't report them. But hey… take that, UFOs!

With average summer temperatures around 45°C, California's Death Valley probably isn't a place you'd want to sit for very long — unless you're trying to solve the mystery of the Sailing Stones. These are rocks that sit in one of the valley's dry lake beds, called the Racetrack. They can weigh up to 320 kilograms, and they seem to move… by themselves.

Of course, they don't move very much. Some can sit in the same spot for decades. But they usually leave long streaks behind them as they travel, and that shows us that some of these rocks have moved more than 450 meters.

For years, people couldn't figure out what was going on. Explanations ranged from hurricane-force winds to films of algae. And to make matters worse, no one had actually seen a rock move.

That is, until a few years ago. In 2011, a team of researchers tried to solve the mystery of the Sailing Stones by sticking. GPS sensors on them and then… just kind of waiting for something to happen.

Since the rocks move so infrequently, one of the paper's authors expected this to be, quote, “the most boring experiment ever”. Two years into the project, a couple of the scientists showed up at the Racetrack to make observations, only to discover the lake bed covered in a thin layer of water. And then, to their amazement… they saw some of the rocks move.

They eventually published their paper — and the solution to the mystery — in PLOS One. According to the team, the Sailing Stones only move under specific circumstances. First, the Racetrack has to fill with water, deep enough to form floating sheets of ice, but shallow enough not to cover the Stones.

At night, the surface of the water has to freeze. Then, in the morning, the ice has to break up into floating panels. Under the right conditions, the wind will push those panels of ice across the surface of the water, and the ice will push the Sailing Stones.

It sounds impossible, but it makes more sense if you realize that the Stones aren't sailing very fast. At most, they move 2 to 6 meters per minute — which you might not notice if you weren't looking closely. But over the years, that can add up, creating those famous, long tracks across the ground.

There is one more mystery that remains, though:. Researchers aren't positive this method also applies to the biggest rocks in Death. Valley.

So there's still one more thing to be solved. With so much of the ocean being unexplored, it makes sense that there's a lot we don't understand about it. And whenever we discover something we can't explain, people are pretty quick to get out their sea monster T-shirts.

That's what happened when we heard the Bloop in 1997. Yes, that is the official term. Because it sounds like… well, a bloop.

The sound was recorded off the coast of South America, while researchers were looking for underwater volcanoes, and it was really loud. It was captured by microphones more than 4800 kilometers apart, making it way too big for something like a ship or a whale. It also didn't help that NOAA at one point announced that the sound was, quote, “possibly biological.” But in 2005, nearly a decade later, scientists found that it definitely wasn't.

As they recorded more sounds in the ocean, especially ones near Antarctica, they concluded that the Bloop was probably an icequake. That's where a huge chunk of ice cracks off a glacier. It makes a ton of noise, and audio recordings taken over several years show that they sound just like the Bloop.

No sea monsters required. Finally, will-o'-the-wisps. You can find stories about them — or something similar — in folklore from around the world, and you may have even seen them yourself if you spend a lot of time in marshes or swamps.

Hey, I don't know your hobbies. They're blue-ish lights that drift over these kinds of landscapes, and if you get too close to one — like Merida in Brave — it will disappear. According to many legends, they're some kind of spirit or creature out to mislead curious travelers.

But in reality, the explanation for these lights... well, actually, it's almost as strange. Because will-o'-the-wisps are probably caused by spontaneous combustion. Not spontaneous human combustion, though — that almost definitely isn't a thing.

Just the regular kind, where something bursts into flame without an obvious source. In this case, the lights are likely caused by certain mixtures of gas reacting with atmospheric oxygen. These mixtures consist of things like methane, carbon dioxide, and, most notably, compounds containing phosphine — like one called diphosphane, which is known to ignite in the presence of oxygen.

Various studies have shown that these gases can be produced in marshes, swamps, and cemeteries, likely by bacteria living in the soil and breaking down organic matter. And when bubbles of that gas make it up to the surface, poof — you have a will-o'-the-wisp. It is worth noting that there are other hypotheses suggesting these lights might not be actual fires, but just clouds of glowing gas.

An experiment published in 1980, for example, showed that you get a sort of glowing green cloud if you mix crude phosphine and methane. But either way, the general mechanism of "swamp gas + air" does seem to explain what's going on. Since these reactions are pretty short-lived, it even explains why these lights seem to disappear if you approach them.

Also, researchers have pointed out that some phosphine derivatives are super toxic. So if dangerous gas clouds kept popping up in local swamps, that might have made people especially eager to stay away. Everybody loves a good mystery, but the stories about how we solve mysteries are pretty fascinating, too.

After all, it takes a lot of curiosity and wonder to become a professional scientist and say “You know what I want to study? The Bloop. Or will-o'-the-wisps.” Thanks for being curious, scientists.

For centuries, people have been telling amazing stories about phenomena like this. And even though scientists can explain how some of them happen, that doesn't make the stories themselves any less worthwhile. Which is why I'm glad that Skillshare has so many classes on storytelling.

Skillshare is actually sponsoring this whole week's worth of videos, so every day this week, we'll be highlighting one of their more than 20,000 classes. They're seriously a great way to learn new skills, brush up on techniques, or discover totally new hobbies. Like, there's one class called called Storytelling 101 that teaches you everything you need to know about storytelling, whether you write about science or the supernatural.

It's by the author Daniel José Older, and besides teaching you some major themes, he also gives you prompts, tips, and follow-up classes to check out. Skillshare also has thousands of other classes on things like art, music, cooking, and tech. And right now, they're offering SciShow viewers two months of unlimited access to every class for free!

So, like, I know what I'm doing for the rest of the day. If you want to join me, you can follow the link in the description. [ outro ].