How the mantis shrimp builds its powerful club, and mysteries of middle Earth
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Science Careers, produced by Science and AAAS, is a free website full of resources to help get the most out of your career. Visit sciencecareers.org today to get started. This is a science podcast for February 7th, 2025. I'm Sarah Crespi. First this week, staff writer Paul Vussen joins me to discuss mapping clogs and flows in the Earth's middle layer, aka the mantle. ♪

Next, the mantis shrimp and its powerful club. Researcher Nicholas Alderate joins me to talk about the material of the mantis shrimp's club and how it uses phononics, specialized microstructures that can eliminate or change high-frequency vibrations to reduce wear and tear when smashing and bashing. The Earth's primary layers, the big three, the crust, where we live...

The mantle underneath making up the bulk of the planet and the core at the center, that's Earth's dynamo, giving us the magnetic fields that, you know, give us the poles. Wait, going back a step, what does the mantle do? Is it just this space in between this filler?

This week in science, staff news writer Paul Vussen wrote about some interesting developments in our understanding of the mantle. Some additional complexity there. Hi, Paul. Welcome back to the podcast. Hello. So I made it very dramatic, but I'm assuming that the mantle was never boring to you, that this is your domain.

Yeah, I mean, really, the mantle is Earth, right? Kind of what, oh, four-fifths of the volume of Earth is the mantle. That's why we have plate tectonics. All these continental plates are floating around on the mantle and then diving down into it getting sucked down.

down and then coming back up again to create new plates. So it's this important part of the earth. And I remember learning about mantle plumes. There's actually some really good graphics of this in the journal. And this is like basically, you know, the mantle comes up, it goes up and it pierces up through the crust and you get Hawaii, right?

Yeah, a big kind of effort for decades was trying to figure out if these hot spots really connected all the way down through the mantle to these plumes. And I mean, it's been widely accepted for more than a decade, really, that they do do this with these advanced seismic techniques. We can see these mantle plumes. So we've always known that tectonic plates, they come up and they go down. And like in subduction zones, you know, like off the coast of Chile, there's

continent going down into the mantle right now. One mystery that's come out of these more advanced techniques is yes, we see stuff going all the way down and up both plates going all the way down plumes going all the way up. But also sometimes they get stuck. They get stuck at like the 660 layer layers like 660 kilometers down 1000 kilometers down, just kind of goes go straight down and stall out get flat.

But some do, some don't. And kind of trying to figure out why that is has been a big question. So much of the new work that we're going to talk about today and in the past few decades is about these seismic waves passing through the Earth, taking deflections, basically. As densities change, as material is passing through changes, you can kind of read that out.

For example, there is this bend in the waves that you talk about at 660 kilometers below the surface. What do we know about what's happening there? Yeah, so this 660 layer is one of the most well-known features of the interior of the plant. People have known about this for half centuries, something like that, more than that. And it's just this kind of clear point where these earthquake waves are passing through and everywhere there they change speed. And that meant to everyone, oh, something is going on there fundamentally.

So the thing about the mantle is it's just full of these really weirdly named minerals. The stuff that only forms under high heat and high pressure, these kind of classic minerals that we might know, some people might know like olivine at the surface, turned into this magmatic stuff, gets turned into different forms. They're kind of crystal structures get rearranged as you move down and down. And this 660 layer, people expected it

to be at this point where this thing called ringwoodite, which is this form of olivine, breaks down into other components. Okay. You kind of have this transition zone where it's the right heat and pressure to take this major element of the mantle and

change it in its physical state in some way. So that's something that we've known about for a while. And then the new work that you wrote about has flagged another interesting change point at around a thousand kilometers in depth. How did this mysterious layer, which we don't know quite as much about, how did that come to light? Yeah. So this is much less understood, accepted, but it's really hard to see down there. That's kind of, it's really murky. Yeah.

You can kind of see the core better than this part of the mantle, really, in some ways with the seismic imaging. And partly this is because there are a lot of seismometers over the oceans. And, you know, there's just a lot of stuff that we're missing. But there have been hints over the past decade that something was going on around this depth. Some evidence that like the speed, the viscosity changed. Some seismic evidence suggesting at least under the Pacific, there might have been like a kind of shift going on there. New work recently published

presented at the AGU meeting late last year now suggests this is a global layer, that there is something going on there. Right. So it's and when you think about a global layer, don't think about a cross section. It is a shell right at 1000 kilometers under the earth, under the surface of the earth. And we see these deflections, but it hasn't been as consistent as the 660 layer. Is that why people aren't so sure about it?

Yeah, it's not nearly as stark. You really have to tease it out of these tomographic models, these like CAT scans of the mantle that people create from seismic waves. But this team did that from three different models that are kind of independent, using different methods, and then ran this machine learning algorithm. So one thing kind of when you're looking for this stuff, in some ways, where you're looking biases what you see, what you're focusing on. They ran this unsupervised machine learning model that I

that unbiasedly kind of looked at everything and pulled out this signal at a thousand kilometers below. And there's supporting evidence to suggest this could be the case. What are some thoughts, hypotheses about why there might be a transition there? Might be something happening? There's not a lot. This is a very emerging area. There was one paper last year that suggested the grain size of the minerals there.

could be changed. And that could be a kind of a fundamental reason. There isn't a known phase transition that happens there. And the key problem is it's really hard to simulate at the surface what's going down on there experimentally. So this is going to be an emerging area. Very cool. I wanted to go back to the 660 line, which people have been studying for longer, and they are doing these kind of surface experiments where they try to recreate some of the circumstances that

intense heat and pressure. But up here with these things called anvils, can you talk a little bit about what they're learning from those experiments? So these experiments, this gets kind of really mineral physics-y quickly, but they have these huge presses in Germany and Japan the past few years

Researchers have been doing kind of better experimentally constraining what happens. There are a few different phase transitions that are actually important at this classic 660 depth. It's pretty nuanced, but people expected this would be pretty orderly, like pressure and temperature would be neatly related to each other. And so if a subducting slab, the old continent getting sucked down is much colder than the surrounding mantle.

So a big thing to step back on here is these phase transitions control the density of this material. It gets more dense, less dense. So if you're shifting the density in a different point, because the slab is at a different temperature and all the surrounding stuff becomes buoyant, it doesn't want to go down. So all this new work with these andals has shown that it's not this kind of easy extrapolation, linear extrapolation. They're kind of bending. They're nonlinear. If it's a little bit colder, it could be very different than if it's a little bit warmer.

That can help explain why this stuff is stalling out. Okay. So there's a lot to learn about the mantle. We'll have to check back in. And the last thing I wanted to talk about was just like a lot of our other reporters here, there's been a ton of changes at the agencies that you cover. So I wanted to touch on policy, a few policy stories that you've been writing about.

We've seen these executive orders coming out of the Trump administration, and they've had impacts on NSF and NASA. Can you talk about your story about what's happening with NASA under these executive orders? Yeah, it's been a really crazy week. Oh, I should note, we are recording on Monday, February 3rd. So if this comes out on Thursday...

and things are totally different, I'm sorry. There's nothing we can do about it. But go ahead. Let's go to NASA first. Yeah. So at NASA, so you have these orders restricting the government from doing DEI activities. They were making steps in conclusion. There's no kind of law ordering them to do this, but they're doing this under Biden. One program that they had started that they were very proud of until recently is called Here to Observe, which would

get students from not big research universities, like smaller institutions, and connect them with mission scientists on different spacecraft working with NASA. And so, you know, this is an amazing opportunity for undergrads to have this exposure to go not

go physically, but they would go to the Zoom meetings of these science teams, watch them discuss how they're interpreting evidence for this formation on Mars that they're looking at, really see what science looks like versus how it's often conveyed as like in a textbook. Right now, this program is in deep limbo. Some of the federal contractors who run some of these missions have already cut off the mission scientists from supporting it. The exact state of what NASA is going to do is not

certain, but it's not promising. All funding is suspended for it right now. And, you know, at least one program officer told his PI that this will likely be canceled. And then there are students on the other side of this who are involved in this through a class, right? That this is something that they're doing for credit. These classes will probably continue. But yeah, the leaders at the institutions, the scientists, the professors who organized this, you know, built classes,

around this. And some of these students are building a radiometer. They may not have the resources to do that anymore. Yeah, this is an example of one kind of reporting that the news team is doing. They're looking across the entirety of all these changes that are happening with the agencies.

And then also going down into these programs where scientists are interacting with the world and seeing what's happening at that level. And I think it's really useful to see that actual hands-on, upfront effect.

Yeah, it can be so abstract sounding. Exactly. When you lose the specifics, then it makes it easier to say things about programs. It makes it easier to overlook. Yeah. Okay, Paul, I think that's it for us. Thank you so much for taking time to talk. Yeah, thank you. Paul Voussin is a staff news writer for Science. You can find a link to the stories we discussed at science.org slash podcast.

Stay tuned for my chat with researcher Nicholas Alderate about how the mantis shrimp makes a powerful biological hammer that just won't quit.

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The peacock mantis shrimp is famous for its bludgeoning club. When hunting, the shrimp whips out this rounded appendage at incredible speed and pounds with immense force on tough-shelled prey like snails or clams.

One of the mysteries of this weapon is how it can exert so much force without breaking itself. This week in science, researcher Nicholas Alderate and his colleagues reveal two details about how the mantis shrimp's powerful club stays intact, blow after blow. Hi, Nicholas. Welcome to the Science Podcast.

Hi, Sarah. Thank you for having me. I'm excited to be here. Oh, yeah, we're happy to have you. You know, I feel like we've had a lot of mantis shrimp papers in the last 10 years. But there's a lot of science. There's a lot of science in here, figuring out how it goes so fast, how it exerts so much force, what that force does. And also their vision is incredibly fascinating. So there's a lot to the story.

to this animal. They're kind of small creatures. They're between 10 and 18 centimeters, but they actually do exhibit some extraordinary features, not only in terms of like the predatorial power that they have, but also, as you mentioned, they're known for having the most advanced vision system in the animal kingdom. Yeah, I always got a little distracted reading about their polarized vision.

when I was supposed to be looking at this club stuff. But let's talk about the forces involved that the club exerts on the prey. You know, can you kind of set up the magnitude of what's happening here? Absolutely. And as you said, this creature has two, what are called, raptorial appendages, which is basically two forelimbs that are going to be used to hit on its prey. Now, in terms of the magnitudes and some rough numbers on this, you can think of the strike of the mantis shrimp as...

Being, let's say, in acceleration, it's equivalent to a .22 caliber bullet. And it can exert forces of up to 1,500 newtons, which is more than 1,000 times its own weight. And so instead of asking, how does it make so much force? You say, how does it withstand so much force? So I actually had to learn about a new field called phononics. Can you describe what that is? Yeah. So the field of phononics is...

You might be more familiar with the sister field, which is called photonics, which has to deal with light. But phononics actually has to deal with, well, phonos come from the Greek sound, so it has to deal with sound or in our case with elastic waves. So the field of phononics basically is going to study the propagation of elastic waves through materials. Right. And there are all kinds of ways of shaping phononics.

or measuring these things. Yeah, one of the things that recently gained a lot of traction is the field of phononic metamaterials. People started looking at how to arrange materials in a way that have these phononic properties. And by phononic properties or phononic behavior, I mean

Kind of like exotic behavior in the sense that you can filter waves, that you can use it for cloaking, or you can use it for sensing. So there's really a range of phononic properties that you can exploit towards engineering functionality. Yeah, this is so interesting. I mean, I learned a lot more about it with regards to light. Like if you think just simply about like structural color,

creating very complex surfaces that are like smaller than the scale of wavelengths of light so that you can interact with light and change its properties using a surface. So not passing it through something, but

but bouncing it off of something. But we're going to apply that to vibrational energy instead of light here? Exactly. That's exactly it. And you do bring up an interesting point. If you actually look at natural systems that exhibit photonic properties so that they can interact with light in these interesting ways, there's a lot more research on those than on photonic biological materials. So when...

When you wanted to check whether or not phononics was at work in the Mantis Club, in this like striking appendages, what were you looking for to say, oh, well, this is looking a little phononic here at the microscale? So what we did was some laser experiments where we would use lasers to launch waves through the structure and we would pick up the waves as they travel through the material with another laser.

And we would be looking for certain signatures in the output that will tell us, okay, this is a phononic result. Now, as to what those signals are, well, we did find evidence of what is called a phononic bandgap.

which is one of the most, I would say, famous traits of a phononic crystal. And that's basically a frequency range in which waves cannot propagate. Right. If you think about a frequency spectrum, just cutting out a piece, you do this with audio all the time. You're like, there's a high-pitched noise. Yeah. I'm going to put a gate on it and I'm going to eliminate that noise. But this is a material that is doing that by interacting with the size, the size of the structure, the shape of the structure.

and it's interacting with the energy wave. So you're able to see that like in the laser readings. What does that say about the actual like structure? What does it look like? Within the phononics community, you have two variants. Either one is a phononic crystal or a phononic metamaterial. For our purpose, let's just talk about phononic crystals. For a phononic crystal to work, you need to have a periodic structure. So basically a very well-ordered structure

arrangement of materials. But we were not sure if the actual structure of the mantis shrimp, even though people know that it has what is called a periodic region, actually is periodic enough to be able to manifest that phonetic behavior.

So we found something that is called block harmonics, which you actually only see in phononic crystals that have been produced or manufactured by micro and nanofabrication strategies. And that's

Block B-L-O-C-H. Is that right? Yeah. Yeah. So you saw this period, periodicity in your signal and in your material, and it all matches up to say this is cutting off some of these frequencies coming through. Yes. What is the manifestation of that? What does that mean in practical terms? You know, what's happening with the club when it impacts on something? Okay. So we did our experiments.

We found these frequency band gaps in the megahertz range, which were super cool. But then we said, okay, how does this relate to the functionality? Why is this useful for the mantis shrimp? So we started going back on the literature and studying what was known about the impact dynamics of these creatures.

One of the things that we found is that the actual strike is comprised of a sequence of events that span like six orders of magnitude in time from the millisecond scale to the nanosecond scale. And actually the mantis shrimp exerts what we call a dual punch. So the first punch would be the actual physical punch when the club pushes or impacts the target. And then because of the velocities involved, you're going to have a cavitation event.

When the club is retracting, it's going to create a region of low pressure in the surrounding fluid, and that's going to create cavitation bubbles. So you're going to have small bubbles in the fluid that are going to collapse. This is something we've talked about recently on the podcast. It's used in, we treat people with this sometimes, with sonic waves. Exactly. You can actually break something up with the cavitation of small bubbles inside the human body. You use it to break things.

So that talks to the nature of the cavitation phenomena, which is actually quite damaging. And this is like another blow to the target or the prey of the mantis shrimp. But it could also hurt the club too. There's nothing that says just because you make cavitation doesn't mean you can't get hurt by it. Right. And this cavitation, what we found is that the implosion of the cavitation occurs over the nanosecond scale. And that correlates very well with the frequency range in which we found these phononic phenomena behavior in the club.

Okay, so basically the frequency range that the phononics in the club are cutting off or reducing, that matches up with what you see from the cavitation. So that means that this is likely the way that the club is protected from that cavitation, those bubbles bursting. There's a lot of material science going on in here. Oh, yeah. But what

is the material? What is it made of? So you can think of it as a boxing glove that's made of three layers. The outer layer is called the impact surface, and that gets worn with the multiple impacts.

And that's actually made of some nanoparticles. Like chitin or something? So note that those are, so in the impact surface, HAB, which is hydroxyapatite nanoparticles, much tougher and harder, which is kind of what you want in a protection system. And then the next layer would be the impact region. And then we have the periodic region. So you have like these three layers. The last two are made of chitin fibers.

which are organic fibers. So many biological systems have chitin. But what is particularly interesting about the periodic region in the shrimp is that these chitin fiber bundles are not arranged in a random fashion. They are arranged helicoidally. Let's say you have a ply of these fiber bundles, and then on top of them, you stack another ply of fiber bundles, but you're going to rotate them by a certain angle. And

And you'll go like this in a sequence and you end up with a helicoidal stacking of these fibers. Super interesting. Which is also periodic. Yeah. For something that occurs naturally, that's fascinating. We're understanding nature. We're understanding how this club works.

We're applying phononics into the natural world. Great. But is this like an approach to phononics that has been used before? Like, have people tried this? So there are phononic materials created with this helicoidal structure, but I would say that none of them have the complexity of the biological system. And this brings up another interesting possibility or opportunity, which is called biophononics, which is actually...

Okay, what if instead of replicating the material, what if we start using or hijacking these materials for the purpose that we want? Or we do some modifications to it, but we use all the tools that nature has to bring it to fruition. Right. So growing this stuff using maybe a different organism, you don't want to necessarily have a bunch of mantis shrimps. What would be a good use case for that?

Let's say that you are able to engineer this tactile club with different sizes. You can sort of move the range of these frequency band gaps to create filters. Oh, not make bigger and bigger clubs. No, no, no, no, no. Like we don't need that. Exactly. But you can change the gating up and down the frequency rate. Oh, very cool. What would that be useful for? Like for instax?

insulating against vibration. Yeah. So protection against vibration. And that goes back to protecting against impacts. And even if you go to lower scales, you can start using these phononic mechanisms even for heat transfer because you can understand heat as a wave. And then you can bring up all these artillery of wave mechanisms into that. But that's at a lower scale. So what's next? What else do you want to learn about this club or phononics or, I don't know, shrimp?

So one of the things that remains is to take a deeper look at the impact dynamics of the club. There has been a number of studies that look at the impact dynamics, but the resolution of the, let's say the instruments was not there to actually go all the way down to the scales that we're interested in. And once you start getting in the realm of dynamic phenomena, there's a lot of things there. So I would expect many papers on Manchester in the future. Thanks, Nicholas. This has been really fun to talk about.

Thank you, Sarah. It was great being here. Nicholas Alderate is currently an associate researcher at the National Institute of Standards and Technology. At the time of the work in this paper, Nicholas was a graduate researcher in theoretical and applied mechanics at Northwestern University. You can find a link to the paper we discussed at science.org slash podcast.

And that concludes this edition of the Science Podcast. If you have any comments or suggestions, write to us at [email protected]. To find us on podcast apps, search for Science Magazine or listen on our website, science.org/podcast. This show was edited by me, Sarah Crespi, Megan Cantwell, and Kevin MacLean. We had production help from Podigy. Our show music is by Jeffrey Cook and Wenkoy Wen.

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