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  • This episode is brought to you by Nature's Fynd,

  • a fungi-based food company for optimists.

  • Click the link in the description to discover the science

  • behind Nature's Fynd fungi-based foods.

  • [♪ INTRO]

  • Geologists love to look at strange rock formations

  • and figure out exactly how they got there.

  • Usually, this is fairly straightforward.

  • Combine a volcanic eruption here with a little bit of erosion there,

  • and boom, you've got yourself a really striking cliff!

  • But not all the features or behaviors of this planet are so easy to figure out.

  • Some have kept geologists scratching their heads for decades or even centuries.

  • And there are some mysteries that even modern scientists haven not solved, yet.

  • In terms of high-priority geological mysteries,

  • the ground randomly exploding seems like it should be near the top of the list!

  • And that's exactly what's happening in parts of Siberia.

  • Massive craters have been appearing in the permafrost, around 20 of them so far!

  • They're up to 90 meters in diameter and 70 meters deep,

  • the aftermath of colossal explosions.

  • Now, few people have witnessed the actual exploding, and never from close up,

  • but one village saw 5-meter flames that burned for an hour and a half!

  • Now, geologists do know that these are from some kind of

  • explosive gas building up under pressure, mostly likely methane.

  • Gas samples from the bottom of one crater were nearly 10% methane.

  • But no one's exactly sure where the gas is coming from,

  • how pockets of it are forming, or where the next one will be.

  • One explanation is this is all the result of melting methane hydrates,

  • which form when methane gas is incorporated into the crystal structure of ice.

  • The methane itself is thought to come from deeper within the Earth.

  • You see, when organic material buried long ago is subjected to extreme heat

  • and pressure underground, it can produce methane which rises upwards

  • to the frozen permafrost, where it can get trapped in ice.

  • And if this is what's happening, then more explosions are probably on the way.

  • With climate change warming the Arctic, methane hydrates are melting faster!

  • But researchers are still debating the details here.

  • Other studies blame microbes for the methane.

  • And some don't think it's really about methane at all.

  • one study points to highly pressurized carbon dioxide as the cause of the explosions.

  • And this is all critical to figure out, and, ya know, fairly soon,

  • because satellites have found 7000 hills that might be ticking time bombs.

  • Until we know what's actually happening,

  • we will not know how many of these are dangerous.

  • What we do know is that these hills form quickly, over a few years.

  • And studying them directly would probably shed some light on things.

  • But they can be under very high pressure, so that's kind of tough.

  • It's like when something is maybe about to explode,

  • a researcher doesn't want to go out there and poke it to take a sample.

  • Because what if you are the next crater?

  • Explosions and impacts are two of the very few things that create

  • near-perfect circles in the Earth, so circular features tend to be worth investigating.

  • Well, it turns out you've been looking part of a near-perfect circle,

  • at least by Earth's standards, every time you look at a map of the world.

  • And once you see this, you will not be able to unsee it.

  • It's called the Nastapoka Arc.

  • It's 650 kilometers long, and makes up a big section of the Hudson Bay in Canada.

  • Clearly, something big happened here.

  • The first idea was that this is an impact crater,

  • the site of a massive thing from space hitting the Earth.

  • There are plenty of other circles that we know formed this way,

  • like nearby Lake Manicouagan.... Another circle on maps that

  • you just won't be able to unsee!

  • But when something hits the Earth, it leaves behind a number of pretty telltale clues.

  • Things like weird rocks thanks to shock metamorphism,

  • when the heat and pressure from a sudden impact deforms

  • and even alters the minerals in rocks.

  • Or, shatter cones, unique patterns of striations on rocks

  • that only form beneath impacts.

  • And the Nastapoka Arc doesn't have either of those!

  • That's left scientists with one other hypothesis:

  • that the curve was once the boundary between two tectonic plates.

  • Essentially, close to 2 billion years ago,

  • two continents may have collided and closed an ancient ocean.

  • And as the plates collided, one was thrust up on top of the other,

  • flexing it into a semi-circle.

  • But circular boundaries between plates aren't common.

  • The idea is that here, as material from one piled up on the other,

  • an unusually massive amount of rock built up in a relatively small area,

  • the center of the circle we see today.

  • This weight of all of that was so much that it pushed the lower plate down

  • in a single spot, creating a semi-circular bend in the crust.

  • Now while that could make sense,

  • other areas where there have been similar plate collisions are not perfect circles.

  • So some geologists still think that this was an impact,

  • perhaps a really ancient one, so the usual evidence has been lost to time.

  • We're left waiting for some adventurous geologist to find either

  • clear evidence of an impact or a unique plate collision

  • to close the loop on this very large, very mysterious circle.

  • Not every mystery can be seen with the naked eye.

  • A patch of the Indian Ocean is missing gravity, and no one's entirely sure why.

  • Now, it's not that you can, like, go here and float.

  • You couldn't even jump any higher if you were standing on a ship there.

  • These are tiny differences that geophysicists detect with very precise instruments.

  • Studying Earth's gravity at different places

  • allows us to see beneath the surface of our planet.

  • See, higher gravity means that something is more dense down there,

  • and vice versa for lower gravity.

  • Except that, earth scientists are totally stumped by

  • the largest gravity anomaly of them all,

  • a massive spot of low gravity in the middle of the Indian Ocean.

  • It could be that the mantle isn't the same in every spot,

  • and there's a plume of hotter, less dense material down there.

  • But some think it goes all the way down through the planet's mantle,

  • essentially suggesting there's a, a dent in the mantle!

  • The idea is that since the outer core is liquid,

  • the boundary between it and the mantle can undulate slowly over time,

  • kind of like it has waves.

  • So the anomaly is the trough of one of those waves.

  • Others think there are slabs of old continents sitting down there

  • that plunged under the crust at the bottom of the ocean

  • around the time of the dinosaurs.

  • Researchers are still learning about what happens to tectonic plates

  • after they've sunk beneath the crust.

  • But, it turns out, they can take hundreds of millions of years

  • to mix back into the mantle.

  • And the hypothesis here is that these subducting slabs bring water down with them.

  • The water can reduce the melting temperature of the rock around it

  • to create buoyant plumes of less-dense magma,

  • and those could be responsible for the low gravity at the surface.

  • There's certainly no shortage of ideas.

  • But determining which one is the right one will require

  • some higher-quality images of what's going on beneath the seafloor.

  • And that's why geophysicists have stuck

  • a bunch of seismometers in the middle of the ocean!

  • They're hoping the way seismic waves from earthquakes interact with

  • whatever is down there will give them clues to what's really going on!

  • Our next mystery takes us to the small island of Anjouan,

  • off the northern coast of Madagascar.

  • See, this island has the wrong type of rock on it.

  • And by that, I mean it is, it is an unexpected type of rock.

  • You see, Anjouan is a volcanic island, but on its surface,

  • you can find a rock called quartzite, which, frankly, it just should not be there!

  • It's pretty clear how the island itself formed:

  • an undersea hot spot volcano slowly built up rock until it made an island,

  • similar to the islands of Hawaii.

  • And this one is relatively young by geologic standards, around 4 million years old.

  • And all this makes Anjouan the last place you would expect to find quartzite.

  • Now that requires some explanation,

  • but not a lot of explanation because quartzite begins as

  • a quartz-rich sedimentary rock like sandstone,

  • and that is formed by quartz grains eroding from a continent

  • and then slowly accumulating at the end of a river.

  • The sandstone is then buried and fused into quartzite under heat and high pressure.

  • And that's the mystery here, the quartz shouldn't have eroded

  • from the volcanic rock of the island itself!

  • It must have come from some larger continent.

  • And besides all of that, the quartzite is likely much older than the island itself.

  • They've been dubbed theimpossible rocksby the researchers studying them,

  • and their history is still very much an unanswered question.

  • The current hypothesis is that they came from the African continent,

  • possibly when Madagascar broke away,

  • but it's not clear how this would have happened.

  • So the next step for the researchers is to figure out exactly how old the quartzite is

  • and compare it to the age of rocks in East Africa and Madagascar

  • to see if they find a match!

  • One of the most long-standing geologic mysteries

  • is also one of the most seemingly mundane.

  • Mima mounds might not look like much at first,

  • they're justmounds of sediment, most famously found in Washington state,

  • though similar formations exist on every continent except Antarctica.

  • Each can be between 2.5 and 15 meters across and up to 3 meters high.

  • So, like, they're just not like, super impressive features?

  • Still, these little bumps have been

  • haunting the dreams of geologists for almost 200 years!

  • We simply don't know how they form!

  • There have been over 50 explanations proposed.

  • Everything from earthquakes shaking the sediment

  • to winds building them during droughts to insects slowly constructing them bit by bit.

  • In 1942, scientists proposed that pocket gophers were responsible!...

  • and believe it or not that is still the leading theory to this day!

  • A 1987 study added small bits of iron to the mounds

  • and tracked them using a metal detector,

  • and that showed that, when the gophers dug a burrow,

  • they pushed the removed material, including the metal bits, uphill!

  • Then, in 2013, a computer model took those results

  • and extrapolated them over hundreds of years.

  • And, at least according to the math,

  • these wee gophers could build that kind of moundeventually.

  • The process is predicted to take hundreds of years,

  • an amazing multi-generational project for the little rodents!

  • We still don't know why the gophers would do this, though.

  • After all, it takes more energy to push sediment uphill when you're digging a burrow.

  • Also, a model is far from conclusive proof, so other ideas could end up being right.

  • So what we really need is for someone to take two flat areas of land,

  • stick some gophers in one and keep gophers out of the other,

  • and then see what happens over about 500 hundred years

  • You know, just some simple, straightforward science

  • that we'd all be long dead before we got the results of!

  • Our final mystery is that every 26 seconds, like clockwork, the Earth rumbles.

  • Seismometers first heard this strange faint pulse, called a microseism, in 1961.

  • Since then, it has been detected all over the world,

  • except, strangely, not in South America.

  • By comparing the signals at different seismic stations,

  • scientists have triangulated the signal's origin.

  • This leads to two spots.

  • The strongest signal from the 1961 pulse was attributed to the Gulf of Guinea,

  • in the Atlantic Ocean, off the coast of Nigeria.

  • The second is in the western Pacific Ocean near Fiji,

  • but that is on the other side of the earth.

  • It's actually exactly on the opposite side of the world from that first spot!

  • So scientists think it could actually be originating in the Gulf of Guinea,

  • and then the seismic waves are traveling across the entire planet

  • and concentrating on the other side!

  • But no one is sure what that ultimate source is

  • or why it occurs at such regular 26-second intervals.

  • One study suggested it could be related to

  • some part of the volcanic process deep beneath the surface.

  • But that wouldn't explain why it is stronger during storms,

  • and overall stronger when it's winter in the southern hemisphere.

  • Instead, those both suggest it has something to do with waves in the ocean.

  • Some experts hypothesize it's simply that the African continental shelf

  • is shaped in such a way that when waves hit it, they rumble through the Earth.

  • A similar, though less impressive rumble coming from the seas around Sicily

  • was tracked down to ocean waves by comparing seismometers

  • to wave data from buoys in the ocean.

  • So that kind of set-up could perhaps shed some light on this 26 second pulse.

  • But the Italian rumble was conveniently close to Mount Etna.

  • That meant researchers were able to repurpose an array of seismometers

  • that was already there to monitor the volcano.

  • Nothing like that exists in the Gulf of Guinea area now,

  • so getting the data needed to support the wave theory won't be so easy.

  • Still, regardless of what's causing them, the microseisms have come in handy:

  • they're so regular that they've been used to

  • sync up the clocks of seismometers around the world!

  • And there you have it!

  • Just six of the many mysteries of this planet that we have yet to solve.

  • Despite having studied Earth for thousands of years, we still have much to learn!

  • It's kind of the same way with agriculture.

  • Yes, we've been at it for millenia,

  • but it turns out that new discoveries can still change everything.

  • Just ask the scientists at Nature's Fynd!

  • They're taking this fungi, first discovered through NASA-funded research,

  • and growing Fy Protein™, which is much better for the environment than meat!

  • Because, let's face it, we don't exactly have room on the planet for more livestock.

  • Their amazing fungi protein is packed with nutrition,

  • and there are no animals required!

  • You can learn all about the process for yourself at the link in the description.

  • [♪ OUTRO]

This episode is brought to you by Nature's Fynd,

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