1 00:00:04,600 --> 00:00:07,600 This is Geology Bites with Oliver Strimpel. 2 00:00:08,760 --> 00:00:12,240 Imagine forcing a piece of material no bigger than a pencil 3 00:00:12,240 --> 00:00:15,640 eraser into a vice that generates pressures and 4 00:00:15,640 --> 00:00:18,520 temperatures equivalent to those at the centre of the earth. 5 00:00:19,800 --> 00:00:23,800 This is what happens at the Z Machine, a facility at Sandia 6 00:00:23,800 --> 00:00:27,600 National Laboratories, and my guest today uses it to 7 00:00:27,600 --> 00:00:31,520 understand what materials are really like deep inside planets. 8 00:00:32,759 --> 00:00:36,400 Most of the material inside the Earth and other rocky bodies 9 00:00:36,400 --> 00:00:40,080 exists under conditions utterly unlike anything on our surface. 10 00:00:40,640 --> 00:00:44,360 Descend just a short distance below the surface, and pressures 11 00:00:44,360 --> 00:00:47,840 and temperatures quickly reach values orders of magnitude 12 00:00:47,840 --> 00:00:51,920 beyond our everyday experience. To understand how different 13 00:00:51,920 --> 00:00:55,480 planets work, why some are geologically dynamic and others 14 00:00:55,480 --> 00:00:58,560 are static, and how their interiors have evolved since 15 00:00:58,560 --> 00:01:02,240 they formed, we really want to replicate those conditions in 16 00:01:02,240 --> 00:01:05,160 the lab and see how familiar materials respond. 17 00:01:05,880 --> 00:01:08,720 And that is the focus of Steve Jacobson's research. 18 00:01:09,520 --> 00:01:12,680 He is a mineralogist and material scientist and a 19 00:01:12,680 --> 00:01:15,520 professor in the Department of Geological Sciences at the 20 00:01:15,520 --> 00:01:19,920 University of Colorado Boulder. What makes his work especially 21 00:01:19,920 --> 00:01:23,000 striking is the range of extremes he tackles. 22 00:01:23,760 --> 00:01:26,880 In this episode, we'll explore three very different 23 00:01:26,880 --> 00:01:28,960 environments he has sought to replicate. 24 00:01:29,840 --> 00:01:32,920 The crushing pressures at the core mantle boundary, nearly 25 00:01:32,920 --> 00:01:35,400 3000 kilometres beneath our feet. 26 00:01:36,280 --> 00:01:39,440 The mantle transition zone, where minerals can lock away 27 00:01:39,560 --> 00:01:44,040 vast quantities of water. And a completely different kind 28 00:01:44,040 --> 00:01:48,400 of extreme The harsh vacuum and radiation of the lunar surface 29 00:01:48,520 --> 00:01:51,880 where NASA's Artemis program hopes to build the permanent 30 00:01:51,880 --> 00:01:54,880 base. Steve Jacobson, welcome to 31 00:01:54,880 --> 00:01:57,280 Geology Bites. It's great to be here, Oliver. 32 00:01:57,280 --> 00:02:00,840 Thank you for inviting me. Let's start at the very bottom 33 00:02:00,840 --> 00:02:03,080 of the mantle, the core mantle boundary. 34 00:02:03,680 --> 00:02:07,880 Why is it important to study this region and how can we try 35 00:02:07,880 --> 00:02:10,560 to comprehend the pressures we're dealing with down there? 36 00:02:11,000 --> 00:02:14,120 The reason why these are interesting environments to 37 00:02:14,120 --> 00:02:17,680 study materials in is because most of the universe, those are 38 00:02:17,680 --> 00:02:21,280 the conditions under which materials persist, including 39 00:02:21,280 --> 00:02:24,400 planets and stars. Now, when we look at our own 40 00:02:24,400 --> 00:02:29,320 planet, the Earth, the biggest boundary really below the crust 41 00:02:29,800 --> 00:02:32,920 is the core mantle boundary. And as you mentioned in the 42 00:02:32,920 --> 00:02:37,400 introduction, it's around 3000 kilometers depth, like flying 43 00:02:37,400 --> 00:02:40,560 from Chicago to Hawaii, but straight down. 44 00:02:41,200 --> 00:02:45,680 The unit of pressure that we use is called a gigapascal, so a 45 00:02:45,680 --> 00:02:48,360 billion pascals. And to put that into 46 00:02:48,360 --> 00:02:54,400 perspective, one giga Pascal translates to about 10,000 bars, 47 00:02:55,040 --> 00:02:56,800 and a bar is about an atmosphere. 48 00:02:56,800 --> 00:03:00,320 So you could think of 1 giga Pascal as being around 10,000 49 00:03:00,320 --> 00:03:04,200 times the squeezing force that the air is putting off your 50 00:03:04,200 --> 00:03:06,760 forearm. Then pressure is force over 51 00:03:06,760 --> 00:03:09,920 area. And so we'll be looking at how 52 00:03:09,920 --> 00:03:13,400 using just the very tiny tip of a diamond with a tip about the 53 00:03:13,400 --> 00:03:17,040 diameter of a human hair that we're able to generate these 54 00:03:17,040 --> 00:03:19,480 pressures and static compression experiments. 55 00:03:20,000 --> 00:03:24,560 The pressure at the core mantle boundary is around 120 56 00:03:24,600 --> 00:03:26,320 gigapascals. It's quite a lot. 57 00:03:26,840 --> 00:03:30,480 And temperatures we know much less well. 58 00:03:30,480 --> 00:03:35,000 That is to say, we can calculate the variation of density or 59 00:03:35,000 --> 00:03:39,600 pressure within the Earth pretty easily just using mechanics, but 60 00:03:39,680 --> 00:03:43,120 the temperature is unknown. We have estimates based on 61 00:03:43,600 --> 00:03:47,360 experiments and theory. For example, if you were to be 62 00:03:47,360 --> 00:03:50,600 able to determine the melting temperature of iron at 120 63 00:03:50,600 --> 00:03:53,120 gigapascals, you'd have a pretty good idea of what the 64 00:03:53,120 --> 00:03:56,440 temperature might be. We estimate the temperatures at 65 00:03:56,440 --> 00:04:01,280 the core mantle boundary to be somewhere between 3 and 4000°C. 66 00:04:01,800 --> 00:04:06,720 So, as I mentioned, you use the Z machine at Sandia National 67 00:04:06,720 --> 00:04:10,680 Laboratories, a facility originally designed to simulate 68 00:04:10,840 --> 00:04:15,080 thermonuclear detonations. Can you walk us through what 69 00:04:15,200 --> 00:04:17,360 actually happens during an experiment? 70 00:04:17,760 --> 00:04:21,519 What it does is it's a very large storage device of 71 00:04:21,519 --> 00:04:25,240 electricity, and it uses a concept called pulse power, 72 00:04:25,440 --> 00:04:31,120 which is to say that if we could compress electrical energy in 73 00:04:31,120 --> 00:04:35,520 space and time to the point where there's a very high 74 00:04:35,880 --> 00:04:40,200 density of energy, we could transfer that energy to a 75 00:04:40,200 --> 00:04:42,560 material and basically blow it up. 76 00:04:43,080 --> 00:04:48,240 And by doing so, understand or measure in situ during a very 77 00:04:48,240 --> 00:04:51,360 brief experiment what some of the thermodynamic properties of 78 00:04:51,360 --> 00:04:54,440 those materials are. So it's plugged into the wall 79 00:04:54,600 --> 00:04:58,200 and it charges up current. The capacitors are able to store 80 00:04:58,200 --> 00:05:00,600 around 20 mega amps of electricity. 81 00:05:00,600 --> 00:05:05,640 That's 20 million amps and the target in the centre of the 82 00:05:05,640 --> 00:05:08,560 machine is meant to be a short, an electrical short. 83 00:05:08,560 --> 00:05:11,320 So imagine if you were to short out two wires, you would see a 84 00:05:11,320 --> 00:05:13,560 spark. That's what the Z machine does. 85 00:05:14,080 --> 00:05:17,480 But along the way it's compressing those 20 mega amps 86 00:05:17,720 --> 00:05:21,600 into a very, very short pulse, just a few nanoseconds in 87 00:05:21,600 --> 00:05:24,600 duration. And by shorting out that current 88 00:05:24,720 --> 00:05:28,720 at around 100,000 volts, we're able to push on the sample to 89 00:05:28,720 --> 00:05:32,120 many, in fact thousands, of giga Pascals. 90 00:05:32,800 --> 00:05:39,120 So traditional shock compression follows something that's known 91 00:05:39,120 --> 00:05:43,720 as the Hugoniot curve, where both pressure and temperature 92 00:05:43,720 --> 00:05:48,160 shoot up together. But I gather the temperatures 93 00:05:48,280 --> 00:05:52,080 that you get that way are much higher than what we'd actually 94 00:05:52,080 --> 00:05:56,960 expect inside the Earth. So you've found a way around 95 00:05:56,960 --> 00:05:59,320 this. Can you explain how you do that? 96 00:06:00,000 --> 00:06:01,240 Yeah, you brought up the Hugoniot. 97 00:06:01,240 --> 00:06:03,560 That's a very important concept in shock physics. 98 00:06:03,800 --> 00:06:07,800 But as you mentioned, the states of pressure density temperature 99 00:06:07,800 --> 00:06:12,600 along the Hugoniot don't quite match what we find to be in the 100 00:06:12,600 --> 00:06:16,520 Earth. The pressure temperature that we 101 00:06:17,000 --> 00:06:20,040 experience when we go down in the Earth is called the 102 00:06:20,040 --> 00:06:23,600 geotherm, and that's basically a measured temperature in a 103 00:06:23,600 --> 00:06:27,480 borehole, for example. But once you go below the crust, 104 00:06:27,800 --> 00:06:31,600 the temperature pressure path follows what we call an adiabat. 105 00:06:31,600 --> 00:06:36,080 An adiabatic compression means there's no flow of heat in or 106 00:06:36,080 --> 00:06:40,840 out during compression. OK, So what we want to try to do 107 00:06:40,840 --> 00:06:43,360 is mimic an adiabat, not the Hugonio. 108 00:06:43,920 --> 00:06:48,960 So how does the experimental setup enable you to depart from 109 00:06:49,320 --> 00:06:52,280 what you get if you just whack the sample with the hammer? 110 00:06:53,040 --> 00:06:55,440 Yeah. There's actually 2 stages of 111 00:06:55,440 --> 00:06:58,960 compression that we're using in our pulse power experiments on 112 00:06:58,960 --> 00:07:03,040 the Z machine. The first step is sort of like a 113 00:07:03,040 --> 00:07:07,480 conventional shock experiment where an impactor reaching many 114 00:07:07,640 --> 00:07:11,240 kilometers per second impacts the sample to produce a 115 00:07:11,240 --> 00:07:14,960 shockwave. So you want to think of Stage 1 116 00:07:15,120 --> 00:07:19,400 as a shock, and that brings the pressure temperature state in 117 00:07:19,400 --> 00:07:21,840 the sample up to some point on the Hugonio. 118 00:07:22,800 --> 00:07:25,920 What's unique about the ZE machine is that we can control 119 00:07:25,920 --> 00:07:31,360 the release of current in a way that leaks out the energy. 120 00:07:31,360 --> 00:07:35,080 Instead of it producing a single sharp pulse, which one might 121 00:07:35,080 --> 00:07:38,840 want to use for a fusion experiment, we can pulse it in, 122 00:07:39,200 --> 00:07:42,600 but then let the rest of the energy slowly creep into the 123 00:07:42,600 --> 00:07:44,600 sample. So what we're going to do is 124 00:07:44,600 --> 00:07:47,760 shock up to some state close to the core mantle boundary 125 00:07:47,760 --> 00:07:52,200 condition and then what we call ramp compress the rest of the 126 00:07:52,200 --> 00:07:55,920 way. It's the ramp compression that's 127 00:07:55,920 --> 00:07:59,000 actually following a pressure temperature curve that's very 128 00:07:59,000 --> 00:08:03,840 close to the Earth's Adia bat. And in order to do that, it's 129 00:08:03,840 --> 00:08:06,720 not only the design of the target, which is the piece of 130 00:08:06,720 --> 00:08:10,600 metal that the sample is sitting on, it's actually V short that 131 00:08:10,600 --> 00:08:13,680 produces the lightning bolt that shocks everything. 132 00:08:14,880 --> 00:08:18,480 So the design of the target itself is what allows us to ramp 133 00:08:18,480 --> 00:08:22,280 compress following the shock. So we call this technique shock 134 00:08:22,280 --> 00:08:25,480 ramp compression. And that enables the pressure to 135 00:08:25,480 --> 00:08:28,680 go up without the temperature shooting up beyond what we 136 00:08:28,680 --> 00:08:31,480 expect to prevail down there. Yeah, that's right. 137 00:08:32,320 --> 00:08:36,559 You also use a completely different approach, diamond 138 00:08:36,720 --> 00:08:41,080 anvil cells, where you squeeze tiny samples between diamonds 139 00:08:41,080 --> 00:08:45,040 under static compression. How does that compare with what 140 00:08:45,040 --> 00:08:49,400 you do on the Z machine, and when would you use one technique 141 00:08:49,400 --> 00:08:52,080 rather than the other? Yeah, the diamond anvil cell is 142 00:08:52,080 --> 00:08:55,840 a very versatile tool. And these static compression 143 00:08:55,840 --> 00:09:00,040 experiments are different principally by the fact that 144 00:09:00,040 --> 00:09:02,920 they are isothermal. And that is to say, if I put a 145 00:09:02,920 --> 00:09:07,240 sample in the diamond anvil cell and I increase the pressure, the 146 00:09:07,240 --> 00:09:09,080 temperature remains room temperature. 147 00:09:09,880 --> 00:09:13,920 And that's because the heat due to compression, unlike an 148 00:09:13,920 --> 00:09:18,880 idiabatic compression, does whisk away into the environment. 149 00:09:18,880 --> 00:09:22,280 So you might have a sample sitting at core mantle boundary 150 00:09:22,280 --> 00:09:24,760 pressures in a diamond anvil cell, but it's at room 151 00:09:24,760 --> 00:09:27,400 temperature. Now, the advantage of the 152 00:09:27,400 --> 00:09:29,920 diamond anvil cell is that there's a lot of different 153 00:09:30,440 --> 00:09:33,520 measurements we can make during compression. 154 00:09:33,960 --> 00:09:37,560 For instance, we might use synchrotron X-ray diffraction to 155 00:09:37,560 --> 00:09:40,360 determine the structure of the material at high pressure. 156 00:09:40,720 --> 00:09:44,040 But the diamonds are also transparent to most of the 157 00:09:44,040 --> 00:09:46,680 electromagnetic spectrum. So we might use optical 158 00:09:46,680 --> 00:09:52,040 techniques, lasers, UV, visible light, infrared light. 159 00:09:52,400 --> 00:09:55,840 There's a lot of different tools that we can perform in situ 160 00:09:55,840 --> 00:09:58,600 experiments on materials under static compression. 161 00:09:58,600 --> 00:10:03,120 Therein lies the real power of the diamond anvil cell. 162 00:10:03,800 --> 00:10:06,040 Now, it's not to say that you can't heat the sample. 163 00:10:06,040 --> 00:10:09,800 Many of my colleagues do heat samples in diamond anvil cells 164 00:10:10,080 --> 00:10:13,040 with lasers or even with resistors. 165 00:10:13,280 --> 00:10:15,520 You know, you can wrap the diamond anvil cell in a little 166 00:10:15,520 --> 00:10:17,480 tungsten wire and heat up the whole thing. 167 00:10:17,480 --> 00:10:20,240 Of course, you can't go to very high temperature that way, 168 00:10:20,240 --> 00:10:23,400 because if you're not careful, the diamonds will burn. 169 00:10:23,400 --> 00:10:27,360 But what happens is that the quality of the physical 170 00:10:27,360 --> 00:10:30,600 properties measurements and the types of physical properties 171 00:10:30,600 --> 00:10:33,800 measurements you can make while heating a diamond anvil cell 172 00:10:33,800 --> 00:10:37,400 become very limited. So we'll go back to the Z 173 00:10:37,400 --> 00:10:40,440 machine for a minute. The advantage of that is that we 174 00:10:40,680 --> 00:10:45,560 can simultaneously achieve a pressure temperature equivalent 175 00:10:45,560 --> 00:10:50,720 to that found at the centre of the Earth while making a density 176 00:10:50,720 --> 00:10:52,880 measurement. And that's one of the key 177 00:10:53,320 --> 00:10:57,360 parameters that we want to know about materials that conditions 178 00:10:57,360 --> 00:11:01,080 of planetary interiors, because what do we know about the core 179 00:11:01,080 --> 00:11:02,520 mantle boundary? Well, there's really only a 180 00:11:02,520 --> 00:11:06,680 couple of things that we know about it based on the 181 00:11:06,680 --> 00:11:10,440 propagation of seismic waves through the Earth. 182 00:11:10,440 --> 00:11:14,760 We know about what compression velocity, the seismic P wave 183 00:11:14,760 --> 00:11:18,560 velocity is, what the seismic S wave velocity is, and we know 184 00:11:18,560 --> 00:11:21,200 what the density is. Those are the three principal 185 00:11:21,200 --> 00:11:24,120 things that we know about the interior of the Earth from 186 00:11:24,120 --> 00:11:26,320 seismology. So that's kind of what we're 187 00:11:26,320 --> 00:11:28,440 after, the sound velocities and the density. 188 00:11:29,440 --> 00:11:33,240 So that reminds me of a previous episode of Geology Bites I did 189 00:11:33,240 --> 00:11:37,360 with Barbara Romanowitz, who talked about how seismic 190 00:11:37,360 --> 00:11:41,040 tomography has revealed a couple of enormous regions near the 191 00:11:41,040 --> 00:11:46,040 core mantle boundary in which seismic waves travel anomalously 192 00:11:46,040 --> 00:11:50,760 slowly, the so-called large low shear velocity provinces. 193 00:11:51,360 --> 00:11:55,080 And at their edges, they're even more extreme, the so-called 194 00:11:55,080 --> 00:11:59,920 ultra low velocity zones. How's your work shed light on 195 00:11:59,920 --> 00:12:01,920 what might be going on in those regions? 196 00:12:01,920 --> 00:12:03,800 Not yet, but that's what we're working on. 197 00:12:03,800 --> 00:12:08,320 The goal of this study is to try to test a couple of different 198 00:12:08,320 --> 00:12:13,040 theories on why those ultra low velocity zones are there, you 199 00:12:13,040 --> 00:12:15,800 know, and what they are. I'll say a few more things about 200 00:12:15,800 --> 00:12:16,920 them. You mentioned already that 201 00:12:16,920 --> 00:12:19,600 they're slow. That is why they're called ultra 202 00:12:19,600 --> 00:12:23,280 low velocity zones. But another thing about them 203 00:12:24,160 --> 00:12:28,840 that I think is kind of strange, they're very dense and normally 204 00:12:29,040 --> 00:12:33,800 seismic velocities follow density in a way where lower 205 00:12:33,800 --> 00:12:37,800 density produces lower velocity. So this is sort of the opposite 206 00:12:38,800 --> 00:12:41,840 trend that one would expect for a material. 207 00:12:41,840 --> 00:12:44,600 So initially there was a couple of theories about why that might 208 00:12:44,600 --> 00:12:49,160 be maybe partial melt, right? Because liquids, molten rock 209 00:12:49,680 --> 00:12:53,280 might be quite slow. Of course, we don't know exactly 210 00:12:53,280 --> 00:12:56,560 what silicate melt sound velocities are at those 211 00:12:56,560 --> 00:12:58,400 conditions. We're working on that now. 212 00:12:58,400 --> 00:13:03,360 But we estimate that they're similar to melts in the Earth's 213 00:13:03,360 --> 00:13:05,480 crust near the Earth's surface, and that they're they're 214 00:13:05,480 --> 00:13:07,400 relatively slow compared to rock. 215 00:13:08,720 --> 00:13:11,440 But the problem with that is that melts are also typically 216 00:13:11,440 --> 00:13:13,600 lower density. So unless something weird 217 00:13:13,600 --> 00:13:16,680 happens at very high pressures and melts become denser than 218 00:13:16,680 --> 00:13:20,720 rock, which might be true, that theory has probably become a 219 00:13:20,720 --> 00:13:24,800 little less intriguing than another which we're testing on 220 00:13:24,800 --> 00:13:27,200 Z. And that is to modify the 221 00:13:27,200 --> 00:13:31,080 composition of the rock in a way that is so extreme it produces 222 00:13:31,080 --> 00:13:33,680 very low velocities but very high density. 223 00:13:34,120 --> 00:13:38,320 And there's one element on the periodic table very, very common 224 00:13:38,320 --> 00:13:40,680 in the Earth, which tends to do that, and that's iron. 225 00:13:41,520 --> 00:13:45,240 Now, iron exists in most minerals. 226 00:13:46,240 --> 00:13:51,640 For example, everyone might know the mineral olivine or purexene 227 00:13:51,840 --> 00:13:53,640 garnets. These are all sort of common 228 00:13:53,640 --> 00:13:55,600 mantle minerals and they all contain iron. 229 00:13:56,480 --> 00:14:00,280 What we have found in laboratory experiments is that when you 230 00:14:00,360 --> 00:14:04,000 increase the fraction of iron relative to magnesium and a 231 00:14:04,000 --> 00:14:09,320 silicate, the density goes up, but the sheer velocities tend to 232 00:14:09,320 --> 00:14:11,880 go down. So the material that we're 233 00:14:11,880 --> 00:14:15,600 putting on the Z machine is called magnesiowustite or 234 00:14:15,600 --> 00:14:18,920 feroparaclase, and it's just an iron magnesium oxide. 235 00:14:18,960 --> 00:14:22,760 So what we want to do is crank up the iron content in the 236 00:14:22,760 --> 00:14:27,880 feroparaclase and measure the speed of sound and the density 237 00:14:27,880 --> 00:14:31,720 on Z as a function of iron content to see if we can line up 238 00:14:31,840 --> 00:14:35,240 the physical properties of feroparaclase with what 239 00:14:35,240 --> 00:14:38,200 seismologists see in the ultra low velocity zones. 240 00:14:39,040 --> 00:14:43,320 That's interesting. So density and seismic wave 241 00:14:43,320 --> 00:14:47,600 velocity usually go hand in hand, but you're suggesting that 242 00:14:47,600 --> 00:14:52,480 these ultra low velocity zones could be not melted but iron 243 00:14:52,480 --> 00:14:54,400 riched. Yes, the theory that we're 244 00:14:54,400 --> 00:14:58,920 testing on iron enrichment really goes back to plate 245 00:14:58,920 --> 00:15:01,720 tectonics itself. We know that the core is full of 246 00:15:01,720 --> 00:15:05,880 iron, mostly iron, and the mantle, the lower most mantle is 247 00:15:05,880 --> 00:15:07,920 made of iron, magnesium silicates. 248 00:15:08,360 --> 00:15:10,160 So this boundary is very interesting. 249 00:15:10,160 --> 00:15:11,880 You know, are they reacting with one another? 250 00:15:11,880 --> 00:15:15,640 Are they in equilibrium? And another thing that could be 251 00:15:15,640 --> 00:15:20,280 going on at the core mantle boundary is a piling up of 252 00:15:20,280 --> 00:15:24,160 subducted oceanic crust where the oceans form crusts. 253 00:15:24,160 --> 00:15:28,080 They are also destroyed at the subduction zones along 254 00:15:28,080 --> 00:15:32,680 convergent pipe boundaries and over the course of geologic 255 00:15:32,680 --> 00:15:37,640 time, we speculate that some of these slabs go all the way to 256 00:15:37,640 --> 00:15:40,280 the core mantle boundary. We can see that in seismic 257 00:15:40,280 --> 00:15:43,800 tomography. And it's possible that once 258 00:15:44,200 --> 00:15:47,160 subducted slabs reach the core mantle boundary, what do they 259 00:15:47,160 --> 00:15:49,520 do? Do they just kind of pile up or 260 00:15:49,520 --> 00:15:52,360 does that material get mixed and come back up in convective 261 00:15:52,360 --> 00:15:54,880 cycles? Well, it's possible that the 262 00:15:54,880 --> 00:15:58,960 basaltic piece of the subducted oceanic crust, if that were to 263 00:15:58,960 --> 00:16:03,280 pile up at the large low shear velocity provinces, we would 264 00:16:03,280 --> 00:16:07,120 have a mechanism for creating iron enrichment in the ultra low 265 00:16:07,120 --> 00:16:09,600 velocity zones. Some people like to call this 266 00:16:09,600 --> 00:16:11,600 theory the slab graveyard theory. 267 00:16:12,080 --> 00:16:14,880 It's where maybe old slabs go to be buried. 268 00:16:15,280 --> 00:16:21,480 Maybe that's what we're seeing. Let's move up to another extreme 269 00:16:21,480 --> 00:16:24,560 environment, the Mantle transition zone. 270 00:16:25,280 --> 00:16:29,040 Can you remind us where the zone sits and what defines it? 271 00:16:29,280 --> 00:16:33,000 The transition zone of the mantle, so-called because 272 00:16:33,320 --> 00:16:36,560 there's a steep change in gradient of seismic velocities, 273 00:16:36,960 --> 00:16:40,840 is what we consider to be the change from the upper mantle to 274 00:16:40,840 --> 00:16:43,840 the lower mantle. The top of the transition zone 275 00:16:44,120 --> 00:16:48,720 occurs at 410 kilometers depth, and the base of the transition 276 00:16:48,720 --> 00:16:51,840 zone occurs around 660 kilometers depth. 277 00:16:52,840 --> 00:16:56,680 The reason I use such specific numbers is because it's defined 278 00:16:56,760 --> 00:17:01,440 by seismic discontinuities. That is to say, when seismic 279 00:17:01,440 --> 00:17:04,960 waves pass through these boundaries, there are strong 280 00:17:04,960 --> 00:17:09,280 reflections and there are strong changes in sound velocity, so 281 00:17:09,280 --> 00:17:11,760 they're probably associated with some sort of change in the 282 00:17:11,760 --> 00:17:14,319 mineralogy. Can you tell us a bit about the 283 00:17:14,319 --> 00:17:17,599 minerals that we think are down there that are changing the 284 00:17:17,599 --> 00:17:20,800 velocity of the seismic waves? We have a pretty good idea. 285 00:17:20,800 --> 00:17:26,280 Even though it's 400 kilometers away, that's within the range of 286 00:17:26,280 --> 00:17:31,080 experiments that are readily available in the laboratory. 400 287 00:17:31,080 --> 00:17:34,840 kilometers to 600 kilometers depth corresponds to pressures 288 00:17:34,840 --> 00:17:38,920 in the range of 12 to 16 giga pascals. 289 00:17:39,440 --> 00:17:41,760 Remember when we were down at the core Mantel boundary, the 290 00:17:41,760 --> 00:17:46,760 pressure was 130 giga pascals. Up in the transition zone, we 291 00:17:46,760 --> 00:17:51,360 can perform what are called large volume experiments that 292 00:17:51,360 --> 00:17:54,240 uses a big hydraulic press, the same kind of press that you 293 00:17:54,240 --> 00:17:56,320 might see, I don't know, car parts being made with. 294 00:17:56,640 --> 00:17:59,120 So rather than a very tiny little diamond anvil cell, 295 00:17:59,320 --> 00:18:04,880 picture now a 5000 ton hydraulic press where you're putting now 296 00:18:04,880 --> 00:18:08,800 not micrometer size samples, but millimeter size samples. 297 00:18:09,200 --> 00:18:14,680 So we have over time as a field, not me kind of mapped if you 298 00:18:14,680 --> 00:18:19,600 will, the mineralogy, the phase diagram against what we observe 299 00:18:19,600 --> 00:18:21,600 seismically. What we can tell is that 300 00:18:21,680 --> 00:18:24,760 olivine, the most abundant silicate in the uppermost 301 00:18:24,760 --> 00:18:28,520 mantle, transforms to a mineral we call watsleite. 302 00:18:29,200 --> 00:18:33,240 It's a modified spinal structure at conditions that correspond 303 00:18:33,240 --> 00:18:38,080 exactly to 410 kilometers depth. Within the transition zone, 304 00:18:38,080 --> 00:18:41,000 there's another phase, another high pressure polymorph of 305 00:18:41,000 --> 00:18:46,080 olivine, because wadsleite becomes unstable around 520 306 00:18:46,080 --> 00:18:49,600 kilometers depth and it forms a mineral we call ringmodite, 307 00:18:49,600 --> 00:18:51,160 which is one of my favorite minerals. 308 00:18:51,480 --> 00:18:56,280 It's blue and it has a very large water storage capacity. 309 00:18:57,200 --> 00:19:02,400 Below 660 kilometers depth, those polymorphs are gone and 310 00:19:02,400 --> 00:19:06,240 every mineral becomes either what we call a bridgemenite 311 00:19:06,360 --> 00:19:07,960 phase. That's like a pyroxene 312 00:19:07,960 --> 00:19:11,040 composition, perovskite structure. 313 00:19:12,000 --> 00:19:15,040 And what's leftover is the oxide we talked about a minute ago, 314 00:19:15,040 --> 00:19:19,280 Pharaoh periclase, this MGFEO. So there's really just two 315 00:19:19,280 --> 00:19:22,440 principal minerals in lowermost mantle, which means the 316 00:19:22,480 --> 00:19:26,600 transition zone from the uppermost mantle to the lower 317 00:19:26,600 --> 00:19:30,120 mantle is a place where there's some pretty unusual minerals, 318 00:19:30,200 --> 00:19:33,280 Wosliite, ringwoodite, majoritic garnet. 319 00:19:34,040 --> 00:19:37,560 Have you been able to study the physical properties of these 320 00:19:37,880 --> 00:19:41,960 strange minerals, wasleite and ringridite, in experiments that 321 00:19:41,960 --> 00:19:43,040 you've done in the lab? Yeah, the. 322 00:19:43,040 --> 00:19:45,920 Reason why I got interested in Wasleite is because in the late 323 00:19:45,920 --> 00:19:49,880 1980s, Joe Smith, who was a professor right here at the 324 00:19:49,880 --> 00:19:53,680 University of Colorado Boulder, predicted that the structure 325 00:19:53,680 --> 00:19:56,840 ought to incorporate large amounts of hydrogen defects. 326 00:19:57,400 --> 00:20:01,760 And by that I mean normally just a magnesium silicate. 327 00:20:02,600 --> 00:20:06,400 It's very likely that that structure would substitute 328 00:20:06,560 --> 00:20:10,800 hydrogen for magnesium defects, and the reason why has to do 329 00:20:10,800 --> 00:20:14,240 with electrostatic potentials. In other words, if we look down 330 00:20:14,240 --> 00:20:18,040 in details, gory details, at the structure of wozlyite, there's 331 00:20:18,040 --> 00:20:21,880 an oxygen atom which is a little bit under bonded. 332 00:20:22,080 --> 00:20:25,240 It's kind of looking for a little bit more cation charge 333 00:20:25,240 --> 00:20:28,120 than it has. When he realized this, that's 334 00:20:28,120 --> 00:20:32,000 when Professor Smith suggested that hydrogen atoms might 335 00:20:32,160 --> 00:20:35,200 balance out that sort of charge imbalance in the structure. 336 00:20:35,200 --> 00:20:37,840 And it wasn't long before people actually made the stuff in the 337 00:20:37,840 --> 00:20:42,520 lab very easily with water putting several thousands of 338 00:20:42,520 --> 00:20:47,880 parts per million or even weight percent of H2O. 339 00:20:48,280 --> 00:20:51,600 Not liquid water, but the compositional ingredients of 340 00:20:51,600 --> 00:20:55,160 water were just going right into the material, sort of like it 341 00:20:55,160 --> 00:20:58,520 was acting like a sponge. So these minerals can actually 342 00:20:58,840 --> 00:21:01,000 effectively store large quantities of water. 343 00:21:01,160 --> 00:21:04,000 In the lab. So now the question is what 344 00:21:04,000 --> 00:21:06,800 about the Earth? And I want to bring us back to 345 00:21:06,800 --> 00:21:09,920 the core mantle boundary. Many years ago, I think it was 346 00:21:09,920 --> 00:21:13,880 Quentin Williams and Ed Garnero who noticed that there was a 347 00:21:13,920 --> 00:21:17,120 very rough geospatial correlation between the ultra 348 00:21:17,120 --> 00:21:20,720 low velocity zones and the ocean islands. 349 00:21:21,160 --> 00:21:25,280 That is places like Hawaii and Iceland where deep sourced 350 00:21:25,280 --> 00:21:28,440 magmas are coming, probably from the core mantle boundary. 351 00:21:29,880 --> 00:21:34,040 So if the ultra low velocity zones are the source of deep 352 00:21:34,080 --> 00:21:37,960 melts in the Earth, those must pass through the transition 353 00:21:37,960 --> 00:21:41,880 zone. And this gets me back to why 354 00:21:41,880 --> 00:21:44,200 water might be important in the transition zone. 355 00:21:45,560 --> 00:21:50,640 Geophysical research has had the perennial problem that magmas 356 00:21:50,640 --> 00:21:53,960 that come from different depths, for example mid ocean Ridge 357 00:21:53,960 --> 00:21:57,280 basalts come from very shallow depths and ocean island basalts 358 00:21:57,280 --> 00:22:01,480 come from very deep depths have different compositions, 359 00:22:02,480 --> 00:22:05,080 especially with respect to isotopes. 360 00:22:05,080 --> 00:22:08,160 Now, that might not sound like a problem, but when you remember 361 00:22:08,160 --> 00:22:11,360 that convection is supposed to be occurring on a whole mantle 362 00:22:11,360 --> 00:22:16,720 scale, how then do you produce different magma types in an 363 00:22:16,720 --> 00:22:20,000 Earth or a planet that is mixed through convection? 364 00:22:21,240 --> 00:22:25,120 It's a dichotomy that the field of geophysics and geochemistry 365 00:22:25,120 --> 00:22:29,160 and mineral physics has been grappling with for decades and 366 00:22:29,160 --> 00:22:31,840 more. Well, the transition zone might 367 00:22:31,840 --> 00:22:35,280 fit in very nicely because if the transition zone were acting 368 00:22:35,280 --> 00:22:39,520 like a sponge for incompatible elements, we call them like 369 00:22:39,520 --> 00:22:46,640 hydrogen, it's possible that it might be stripping away some of 370 00:22:46,640 --> 00:22:51,160 the incompatibles as melts are ascending through the entire 371 00:22:51,160 --> 00:22:54,320 mantle from the core mantle boundary and almost like 372 00:22:54,320 --> 00:22:58,680 trapping it there, if you will. I want to associate that idea 373 00:22:58,680 --> 00:23:03,000 with Shun Corrado. And David Bercovici at Yale some 374 00:23:03,000 --> 00:23:05,800 years ago wrote a paper that they called the transition zone 375 00:23:05,800 --> 00:23:10,880 water filter model. And it was a very nice theory on 376 00:23:10,880 --> 00:23:15,200 how the transition zone might not only be acting as a large 377 00:23:15,200 --> 00:23:19,600 reservoir of H2O in the Earth, with implications for the the 378 00:23:19,600 --> 00:23:23,480 origin of Earth's water, but also acting as one of these ways 379 00:23:23,480 --> 00:23:26,760 in which we can produce different compositions of magma 380 00:23:27,200 --> 00:23:29,560 in a whole mantle convection planet. 381 00:23:30,240 --> 00:23:33,800 Wow, that's fascinating. So kind of dual role of this 382 00:23:33,880 --> 00:23:37,560 mantle transition zone is a kind of sponge, but also as a filter, 383 00:23:37,560 --> 00:23:40,680 Yeah, I think. That you can't have oceans on a 384 00:23:40,680 --> 00:23:45,360 planet until the mantle is saturated. 385 00:23:45,360 --> 00:23:49,240 Imagine trying to put a little lake on a sponge. 386 00:23:49,800 --> 00:23:52,440 As you add water to the sponge, it would just kind of get 387 00:23:52,440 --> 00:23:55,600 absorbed by the sponge until the sponge is saturated, and only 388 00:23:55,600 --> 00:23:58,960 then would you be able to put a film of liquid water on the top 389 00:23:58,960 --> 00:24:01,280 of it. It's possible planets might act 390 00:24:01,280 --> 00:24:05,520 the same way, and that the inside of the planets that have 391 00:24:05,520 --> 00:24:08,440 liquid water on their surfaces might need something like the 392 00:24:08,440 --> 00:24:12,800 transition zone, and therefore planets only of a certain size 393 00:24:12,920 --> 00:24:15,440 might be able to have liquid water on their surface. 394 00:24:16,440 --> 00:24:20,240 That's interesting. So does that mean that a planet 395 00:24:20,240 --> 00:24:25,240 really needs to have this kind of a sponge system to regulate 396 00:24:25,480 --> 00:24:30,120 how much water it has, or to allow water to exist in liquid 397 00:24:30,120 --> 00:24:32,080 form on the surface? I mean, are those two things 398 00:24:32,080 --> 00:24:34,520 connected at all? It's it's a theory that people 399 00:24:34,520 --> 00:24:37,960 are working on from modeling perspectives and experimental 400 00:24:37,960 --> 00:24:40,760 perspectives. Let's look at Mars. 401 00:24:40,840 --> 00:24:45,480 Mars is not as big as the Earth. Mars mantle barely gets to the 402 00:24:45,480 --> 00:24:49,400 pressure high enough to support ringwoodite near the core. 403 00:24:49,880 --> 00:24:52,520 So there is no transition zone in Mars. 404 00:24:53,320 --> 00:24:58,000 And going one step further, the origin of Earth water was long 405 00:24:58,240 --> 00:25:01,640 supposed to have come from comets after and during 406 00:25:01,640 --> 00:25:05,240 accretion. But this idea that at extreme 407 00:25:05,240 --> 00:25:08,720 conditions minerals can incorporate the components of 408 00:25:08,720 --> 00:25:12,240 water hydrogen leads us to think about that again. 409 00:25:12,240 --> 00:25:15,640 And it's quite possible that planets could retain quite a lot 410 00:25:15,640 --> 00:25:18,480 of their original water. Now that we have more 411 00:25:18,480 --> 00:25:22,000 appreciation for the properties of melts and minerals at 412 00:25:22,000 --> 00:25:23,960 conditions of deep planetary interiors. 413 00:25:23,960 --> 00:25:27,080 They seem to be quite happy holding on to the water and we 414 00:25:27,080 --> 00:25:31,480 might not needed to have degassed all the hydrogen during 415 00:25:31,480 --> 00:25:33,520 accretion, which is what we thought previously. 416 00:25:34,240 --> 00:25:36,160 That's interesting. It reminds me of previous 417 00:25:36,160 --> 00:25:39,880 episodes about the origin of the Earth's water, both the 418 00:25:40,320 --> 00:25:44,680 meteorite origin. Sarah Russell talked about that 419 00:25:44,680 --> 00:25:48,200 and then Lindy Elkins talked very much about the fact that 420 00:25:49,040 --> 00:25:53,560 the the Earth was had its water and Anat Shahar about a way in 421 00:25:53,560 --> 00:25:56,960 which it could make its water from a magma ocean and a 422 00:25:56,960 --> 00:26:00,760 hydrogen atmosphere. So it seems like there are many, 423 00:26:00,760 --> 00:26:03,400 many different theories really as to how the Earth got its 424 00:26:03,400 --> 00:26:06,360 water and and understanding the mineral properties of the 425 00:26:06,360 --> 00:26:08,880 transition zone pretty plays into that discussion. 426 00:26:09,400 --> 00:26:11,880 Just to step back to the experimental side for a moment, 427 00:26:11,880 --> 00:26:16,080 I'm reminded of the episode I did with David Kolstad, who also 428 00:26:16,080 --> 00:26:20,320 does high pressure experiments. Can you say how your approach 429 00:26:20,320 --> 00:26:22,760 differs from his? Yeah, Professor Kolstadt is a 430 00:26:22,760 --> 00:26:26,680 rock mechanics expert and he studies what we call rheology. 431 00:26:26,880 --> 00:26:33,520 So he studies the way solids deform plastically beyond their 432 00:26:33,520 --> 00:26:37,680 elastic limit. All of the deformation that I'm 433 00:26:37,680 --> 00:26:41,000 performing to the diamond anvil cell under static compression 434 00:26:41,000 --> 00:26:45,880 experiments, when we squeeze at room temperature a sample, a 435 00:26:45,880 --> 00:26:50,120 crystal of olivine, say to 10 gigapascals and bring it back, 436 00:26:50,400 --> 00:26:55,680 that's a fully elastic process. The propagation of seismic waves 437 00:26:55,680 --> 00:26:59,800 is also an elastic process in the sense that as the wave moves 438 00:26:59,800 --> 00:27:03,400 through the material, there's compression and there's 439 00:27:03,400 --> 00:27:10,280 dilation, but those changes are completely reversible or 440 00:27:10,280 --> 00:27:12,720 elastic. And what David does is push 441 00:27:12,720 --> 00:27:17,040 rocks to their elastic limit and then studies what happens 442 00:27:17,040 --> 00:27:20,000 thereafter. Now, that's very important in 443 00:27:20,000 --> 00:27:22,880 the context of mantle convection because there are places in the 444 00:27:22,880 --> 00:27:29,280 uppermost mantle and crust where shear stresses are so high that 445 00:27:29,280 --> 00:27:31,200 there's plastic deformation going on. 446 00:27:31,200 --> 00:27:33,320 We can see that. And you go outside and look at 447 00:27:33,320 --> 00:27:37,680 metamorphic rocks and fabric forming in very high stress 448 00:27:37,680 --> 00:27:40,760 shear zones. So there's a contrast between 449 00:27:40,760 --> 00:27:44,640 work in rock mechanics that deals with those rheological 450 00:27:44,640 --> 00:27:48,000 properties, and mineral physics which deals with more 451 00:27:48,000 --> 00:27:52,680 fundamental intensive physical chemical properties such as 452 00:27:52,920 --> 00:27:56,520 density, thermal conductivity, heat capacity and so on. 453 00:27:57,800 --> 00:28:01,760 So far we've been talking about the extreme pressures deep 454 00:28:01,840 --> 00:28:05,920 inside planets. Let's now shift to a completely 455 00:28:05,920 --> 00:28:08,920 different kind of extreme the surface of the moon. 456 00:28:09,800 --> 00:28:12,640 What makes that such a challenging environment for 457 00:28:12,640 --> 00:28:16,800 materials? The challenge posed by doing 458 00:28:16,800 --> 00:28:21,360 geology just even on the surface of the Moon, comes mainly from 459 00:28:21,800 --> 00:28:24,560 low temperatures, high radiation. 460 00:28:25,160 --> 00:28:29,200 It's very far away. And one of the goals of Artemis 461 00:28:29,200 --> 00:28:34,040 is to learn how to get people onto the moon and off to Mars. 462 00:28:34,040 --> 00:28:36,680 And so we have to kind of practice everything on the moon. 463 00:28:37,000 --> 00:28:39,520 First thing you need to be able to do is land a rocket in the 464 00:28:39,520 --> 00:28:44,040 same place multiple times. We need a base and the regolith, 465 00:28:44,240 --> 00:28:46,320 the, the lunar soil, if you will. 466 00:28:47,160 --> 00:28:48,680 It's just basically crushed rock. 467 00:28:48,840 --> 00:28:51,840 It's very harmful. It's very brittle. 468 00:28:51,840 --> 00:28:56,200 I mean, it's just nasty, glassy shards of minerals that if you 469 00:28:56,200 --> 00:28:59,640 were set up at a camp already and I were to arrive with the 470 00:28:59,640 --> 00:29:02,960 rocket a bit later and land without a landing pad, I would 471 00:29:02,960 --> 00:29:07,560 sandblast the camp. So we're working in the area of 472 00:29:07,600 --> 00:29:11,600 additive manufacturing. To develop the technology for 473 00:29:11,600 --> 00:29:16,280 building a landing pad or a base on the moon requires using fake 474 00:29:16,280 --> 00:29:18,680 lunar soil. We can't really work with the 475 00:29:18,680 --> 00:29:20,760 real thing. So one of the things we're doing 476 00:29:20,760 --> 00:29:23,200 is trying to understand simulants. 477 00:29:23,760 --> 00:29:28,360 Those simulants are being then melted using a laser to produce 478 00:29:28,360 --> 00:29:30,240 a rock. And I'm actually holding one in 479 00:29:30,240 --> 00:29:33,680 my hand right now and looking at one of these lunar bricks, if 480 00:29:33,680 --> 00:29:36,360 you will. It's pretty dark and it's kind 481 00:29:36,360 --> 00:29:39,120 of layered. The layers have slightly 482 00:29:39,120 --> 00:29:41,880 different shades. The rock has basically the 483 00:29:41,880 --> 00:29:45,480 composition of a mixture of basalt and an orthocyte. 484 00:29:45,480 --> 00:29:49,440 But it's layered because the process we're using is called 485 00:29:49,880 --> 00:29:54,040 powder bed fusion. So imagine a sandbox of 486 00:29:54,040 --> 00:29:59,320 regolith, of lunar regolith that you then use the laser to scan 487 00:29:59,560 --> 00:30:02,280 and melt. And where those melt pools form, 488 00:30:02,280 --> 00:30:06,880 we can dash more material in and build up a solid material one 489 00:30:06,880 --> 00:30:10,040 layer at a time. And this is how we're working 490 00:30:10,040 --> 00:30:12,200 towards developing 3D printing on the Moon. 491 00:30:12,800 --> 00:30:16,120 Now obviously the lunar surface is a totally different 492 00:30:16,120 --> 00:30:18,120 environment. As you said, it's a vacuum. 493 00:30:18,560 --> 00:30:21,120 It's subject to extreme radiation. 494 00:30:21,800 --> 00:30:26,320 Does that change the material? Is it something that makes it 495 00:30:26,320 --> 00:30:29,120 really different from what we can simulate here on Earth? 496 00:30:29,440 --> 00:30:31,400 It does. We call that space weathering. 497 00:30:31,680 --> 00:30:33,960 You know, on Earth, when we talk about weathering, we're talking 498 00:30:33,960 --> 00:30:39,840 about the reaction of rocks with water and the atmosphere and the 499 00:30:39,840 --> 00:30:43,520 transport of that material through gravity on the moon. 500 00:30:43,520 --> 00:30:46,040 When we talk about weathering or space weathering, we're really 501 00:30:46,040 --> 00:30:50,040 talking about modifications due to radiation from the sun. 502 00:30:50,520 --> 00:30:55,720 Those may include bombardment from high energy particles, 503 00:30:56,000 --> 00:30:58,400 hydrogen, helium ions for example. 504 00:30:59,000 --> 00:31:01,880 There is also a continuous stream of micrometeorite 505 00:31:01,880 --> 00:31:04,120 bombardment on the surface of the moon. 506 00:31:04,440 --> 00:31:08,520 And all of these processes modify the regolith in turn 507 00:31:08,640 --> 00:31:12,360 because there is no weathering in the Earth perspective. 508 00:31:12,400 --> 00:31:14,840 That is to say that the regolith sitting on the surface of the 509 00:31:14,840 --> 00:31:16,760 Moon has been there for 4 1/2 billion years. 510 00:31:17,560 --> 00:31:21,200 So it's highly modified through ion bombardment and 511 00:31:21,200 --> 00:31:25,680 micrometeorite bombardment. The regolith simulant, the fake 512 00:31:25,680 --> 00:31:29,320 stuff that we're working with to the 3D print is not space 513 00:31:29,320 --> 00:31:31,440 weathered and we are very concerned about what that might 514 00:31:31,440 --> 00:31:36,520 mean for the engineering. One of the things we see in real 515 00:31:36,600 --> 00:31:40,360 lunar regolith is little tiny particles, actually nanoscale 516 00:31:40,360 --> 00:31:42,480 particles of iron on the surfaces. 517 00:31:42,920 --> 00:31:46,120 This nanophase iron would certainly have a big impact on 518 00:31:46,120 --> 00:31:49,840 the laser heating properties of the 3D printing process. 519 00:31:49,840 --> 00:31:53,920 So we'd like to try to simulate space weathering in the lab. 520 00:31:54,120 --> 00:31:57,280 We actually have built a very large vacuum chamber inside 521 00:31:57,280 --> 00:31:59,600 which we're doing this laser 3D printing. 522 00:32:00,000 --> 00:32:03,200 What we find, for example, is that a lot of the elements that 523 00:32:03,200 --> 00:32:06,960 are volatile potassium, sodium, I mean, they immediately boil 524 00:32:06,960 --> 00:32:09,960 off during this process. So there's almost like a whole 525 00:32:09,960 --> 00:32:15,520 new patrology that we have to explore under vacuum in order to 526 00:32:16,360 --> 00:32:18,800 work with these materials on the surface of the moon. 527 00:32:19,680 --> 00:32:23,200 Some of the experiments you do to understand planetary 528 00:32:23,200 --> 00:32:27,720 interiors have created materials that have never existed before. 529 00:32:28,480 --> 00:32:30,760 Can you give us an example? Sure. 530 00:32:30,760 --> 00:32:34,160 Let me just start with one that is in full scale production. 531 00:32:34,760 --> 00:32:39,080 The field of super hard materials has to do with 532 00:32:39,080 --> 00:32:42,400 abrasives or materials that might be able to withstand very 533 00:32:42,400 --> 00:32:45,600 high pressure temperatures without degradation. 534 00:32:45,920 --> 00:32:49,480 We think of diamond an extreme material, but in fact diamond 535 00:32:49,480 --> 00:32:52,280 burns pretty easily. Diamond will start to burn in 536 00:32:52,280 --> 00:32:55,560 air around 700°C even though it's the hardest known 537 00:32:55,560 --> 00:32:58,440 substance. And so the field of super hard 538 00:32:58,440 --> 00:33:02,480 materials pertains to it doesn't necessarily have to be harder, 539 00:33:02,480 --> 00:33:04,840 it just has to have higher thermal stability. 540 00:33:06,120 --> 00:33:10,400 Cubic boron nitride is a good example of a material that was 541 00:33:10,400 --> 00:33:13,320 discovered through high pressure temperature synthesis. 542 00:33:13,840 --> 00:33:17,200 It has a hardness very close to that of diamond, but it's stable 543 00:33:17,200 --> 00:33:22,600 up to like 1300°C. Now you need 5 or 6 gigapascals 544 00:33:22,640 --> 00:33:26,440 of pressure and 1200°C to make it. 545 00:33:26,440 --> 00:33:30,400 And so commercially, it's not easy, but it's set a scale where 546 00:33:30,400 --> 00:33:33,080 you can buy cubic boron nitride parts. 547 00:33:34,080 --> 00:33:38,080 The idea that we can study materials in extreme 548 00:33:38,080 --> 00:33:41,040 environments of pressure, temperature, radiation and so on 549 00:33:41,040 --> 00:33:46,640 to learn about the universe can be flipped around and put in a 550 00:33:46,640 --> 00:33:50,360 way that we use those extreme conditions to create new 551 00:33:50,360 --> 00:33:52,400 materials with functional properties. 552 00:33:52,400 --> 00:33:57,200 And there's a whole suite of ferroelectrics, thermoelectrics, 553 00:33:57,400 --> 00:34:01,800 super hard materials, materials with exotic magnetic states, 554 00:34:02,040 --> 00:34:06,520 superconductors and so on that are being generated in these 555 00:34:06,520 --> 00:34:08,159 very high pressure temperature states. 556 00:34:08,159 --> 00:34:11,040 And so there's a whole branch of material science that comes out 557 00:34:11,159 --> 00:34:12,960 of materials in extreme environments. 558 00:34:13,600 --> 00:34:16,840 What are you most excited about working on at the moment? 559 00:34:17,679 --> 00:34:22,080 I'm excited by the fact that we continue to make breakthrough 560 00:34:22,080 --> 00:34:25,520 discoveries in science. When I look back and I think 561 00:34:25,520 --> 00:34:30,040 about how much has changed in our knowledge about the Earth, 562 00:34:30,040 --> 00:34:33,719 the mantle, the composition of the mantle, and the technology 563 00:34:33,719 --> 00:34:38,440 we've developed everything from materials discovery to stuff we 564 00:34:38,440 --> 00:34:42,639 just talked about 3D printing bricks or conducting compression 565 00:34:42,639 --> 00:34:46,560 experiments where we measure sound velocities directly at 566 00:34:46,560 --> 00:34:50,360 core mantle boundary conditions. I mean, in hindsight, that would 567 00:34:50,360 --> 00:34:52,360 have looked like science fiction to me. 568 00:34:52,679 --> 00:34:56,080 And I think that that's of course going to just continue. 569 00:34:56,080 --> 00:35:00,360 So graduate students today can think about that for a minute, 570 00:35:00,360 --> 00:35:05,560 that that what they'll be doing maybe 2025 years from now might 571 00:35:05,920 --> 00:35:07,400 sound like science fiction to us. 572 00:35:07,400 --> 00:35:09,200 Now. That's what I get excited about. 573 00:35:10,120 --> 00:35:12,040 Steve Jacobson, thank you very much. 574 00:35:12,160 --> 00:35:14,160 Thank you, Oliver. It's been really fun to talk to 575 00:35:14,160 --> 00:35:16,920 you. To see pictures and 576 00:35:16,920 --> 00:35:22,320 illustrations that support this podcast, go to geologybytes.com, 577 00:35:22,440 --> 00:35:25,200 where you'll also find a subject matter index of all the 578 00:35:25,200 --> 00:35:27,560 episodes. There you can also give me 579 00:35:27,560 --> 00:35:31,480 feedback which I welcome, as well as sign up to get my emails 580 00:35:31,480 --> 00:35:32,720 about new episodes.