1 00:00:04,200 --> 00:00:07,500 This is geology, B. I'm all of us trampled. 2 00:00:08,600 --> 00:00:11,700 People who study the Earth, have an enormous advantage over those 3 00:00:11,700 --> 00:00:15,200 who study other celestial bodies such as other planets and the 4 00:00:15,207 --> 00:00:17,900 Stars. That's because we live on the 5 00:00:17,900 --> 00:00:20,100 earth. So we can explore its surface at 6 00:00:20,100 --> 00:00:24,700 will sample and analyzes rocks. Listen to its earthquakes and 7 00:00:24,700 --> 00:00:27,500 drill holes into it, to get at least a few miles below the 8 00:00:27,500 --> 00:00:30,600 surface. So why would we want to look to 9 00:00:30,600 --> 00:00:33,500 another planet or even to another solar system to help us 10 00:00:33,500 --> 00:00:37,300 understand the Earth down? Mackenzie is Professor of Earth 11 00:00:37,300 --> 00:00:41,600 Sciences at University, the best known for discovering the theory 12 00:00:41,600 --> 00:00:44,200 of plate. Tectonics in the late 1960s. 13 00:00:44,600 --> 00:00:48,000 He is also among many other subjects, made fundamental 14 00:00:48,000 --> 00:00:51,500 contributions to our understanding of the Moon, Mars, 15 00:00:51,500 --> 00:00:55,400 and Venus Dan. Mackenzie welcome to geology B. 16 00:00:55,600 --> 00:00:57,700 Thank you. I know one shouldn't really 17 00:00:57,700 --> 00:01:00,900 attach labels to people but I think of you as an earth 18 00:01:00,900 --> 00:01:03,300 scientist. So when you first turn your 19 00:01:03,300 --> 00:01:05,300 attention to Venus, did you do that? 20 00:01:05,300 --> 00:01:07,900 Because you are anyway, expanding your research beyond 21 00:01:07,900 --> 00:01:10,100 the Earth. Or was it because you actually 22 00:01:10,100 --> 00:01:12,900 thought Venus might offer us some Clues as to how things work 23 00:01:12,900 --> 00:01:16,000 here on Earth. My interest is being in 24 00:01:16,000 --> 00:01:19,900 essentially how the rocky planets behave and if you work 25 00:01:19,900 --> 00:01:25,800 on the earth who got one, you've no idea how special and what 26 00:01:25,800 --> 00:01:29,100 actually governs things here. And whether if you had another 27 00:01:29,100 --> 00:01:32,000 rocky planet, whether it would look the same, it's always a 28 00:01:32,000 --> 00:01:37,300 help to look at more than one thing that was really why I got 29 00:01:37,300 --> 00:01:39,900 interested. I'd always been interested in 30 00:01:39,900 --> 00:01:44,000 Venus, but the problem with Venus is that it's covered with 31 00:01:44,000 --> 00:01:48,200 clouds made out of sulfuric acid and these never clear. 32 00:01:48,700 --> 00:01:54,400 So nobody had the slightest idea before radar as to what was 33 00:01:54,400 --> 00:01:58,100 underneath the clouds. So yes, we knew how big it was. 34 00:01:58,100 --> 00:02:00,700 It's more or less the same size as the Earth, more or less, the 35 00:02:00,700 --> 00:02:04,600 same mass of the Earth. And if the next plan is in, from 36 00:02:04,600 --> 00:02:07,800 the earth, towards the Sun. So it seemed really quite likely 37 00:02:07,800 --> 00:02:11,700 that We would learn something by looking at Venus and that was 38 00:02:11,700 --> 00:02:14,700 really why I applied to be an investigational Magellan 39 00:02:14,700 --> 00:02:18,800 program, which was a spacecraft, which would being sent to Venus. 40 00:02:19,200 --> 00:02:22,300 So, with Magellan, we finally could look under the clouds as 41 00:02:22,300 --> 00:02:25,900 you say with radar and it was very successful at doing that, 42 00:02:26,300 --> 00:02:30,500 the main purpose was to map the surface, but you had an idea 43 00:02:30,500 --> 00:02:33,500 that we could do something else with the data that was sent back 44 00:02:33,500 --> 00:02:35,700 from the spacecraft. Once it was in orbit around 45 00:02:35,700 --> 00:02:41,800 Venus, I was more interested In the interior of the planet. 46 00:02:41,900 --> 00:02:46,800 Because on Earth, the plates are moved by convective forces. 47 00:02:47,700 --> 00:02:51,100 And what I wanted to know was whether the same things 48 00:02:51,300 --> 00:02:55,100 happening on Venus and if so, we could learn a lot about it 49 00:02:55,100 --> 00:02:58,200 because we didn't really understand what actually 50 00:02:58,200 --> 00:03:02,600 controlled the plate motions that we can see it all going on, 51 00:03:02,600 --> 00:03:07,800 but it was really quite strange notion that cats. 52 00:03:08,100 --> 00:03:12,000 So Caps of the earth whose distance across is perhaps 53 00:03:12,000 --> 00:03:14,400 10,000 kilometers like the Pacific. 54 00:03:14,500 --> 00:03:17,200 Just to be clear. These spherical caps are the 55 00:03:17,200 --> 00:03:19,600 plates of plate tectonics. Yes. 56 00:03:20,200 --> 00:03:24,000 And the elastic part of these things is about 30 kilometers 57 00:03:24,000 --> 00:03:27,900 thick, that these should actually move as rigid caps as 58 00:03:27,900 --> 00:03:31,000 most extraordinary notion. We're all quite used to it now 59 00:03:31,000 --> 00:03:33,500 because, you know, we can actually see that motion with 60 00:03:33,500 --> 00:03:37,800 GPS with earthquakes and things, but before we actually could see 61 00:03:37,800 --> 00:03:39,700 it. I mean, nobody really would have 62 00:03:39,700 --> 00:03:42,600 taken that seriously. So what actually controls what's 63 00:03:42,600 --> 00:03:46,700 going on that was what interested me is where the Venus 64 00:03:46,700 --> 00:03:50,700 was doing the same thing and if so could we learn about what was 65 00:03:50,700 --> 00:03:54,800 going on from essentially looking at the gravity field, 66 00:03:54,800 --> 00:03:57,100 which is something that you get for free. 67 00:03:57,200 --> 00:04:00,100 There goes base. Craft going around in orbit 68 00:04:00,100 --> 00:04:04,200 around the planet, Venus undergoes the acceleration due 69 00:04:04,200 --> 00:04:08,100 to gravity. But the gravity field of planets 70 00:04:08,400 --> 00:04:13,800 Venus of the earth is not just that of a point Mass, it 71 00:04:13,800 --> 00:04:16,800 actually all the things like mountains and stuff or produce 72 00:04:16,800 --> 00:04:19,399 gravity Fields. So you can learn the very great 73 00:04:19,399 --> 00:04:23,000 deal about what's going on inside the planet by looking at 74 00:04:23,000 --> 00:04:25,800 the gravity field, which is controlled by essentially 75 00:04:25,800 --> 00:04:29,400 density variations inside the planet and that was what I hope 76 00:04:29,400 --> 00:04:33,000 to be able to do. But the mountains on Earth and 77 00:04:33,000 --> 00:04:35,900 on Venus are pretty small compared to the planets 78 00:04:35,900 --> 00:04:38,300 themselves. So these must have been pretty A 79 00:04:38,308 --> 00:04:43,000 small fluctuations or they're not very big on Earth the few 80 00:04:43,000 --> 00:04:47,600 parts in 100,000, there's a method by which you can actually 81 00:04:47,600 --> 00:04:51,600 track the spacecraft using Doppler and you can measure the 82 00:04:51,600 --> 00:04:55,400 velocities of the spacecraft at the other side of the solar 83 00:04:55,400 --> 00:05:00,800 system to a few tens of microns. The second set is perhaps a foot 84 00:05:00,800 --> 00:05:03,800 an hour is about the source of be that you've measure. 85 00:05:04,000 --> 00:05:07,200 And if you take the change with time, that tells you the 86 00:05:07,200 --> 00:05:12,000 acceleration, In the direction which are looking so by using 87 00:05:12,000 --> 00:05:15,400 this, which is actually how NASA navigates it spacecraft. 88 00:05:15,400 --> 00:05:17,200 So I didn't have to do anything special. 89 00:05:17,200 --> 00:05:21,000 They were doing this anyway. You can actually see the gravity 90 00:05:21,000 --> 00:05:25,600 field of the planet directly as a sort of map from the way that 91 00:05:25,600 --> 00:05:28,700 you're looking. And this was what really 92 00:05:28,700 --> 00:05:33,900 interested me. But the problem was that when 93 00:05:34,000 --> 00:05:37,700 they spacecraft was closest to Venus. 94 00:05:37,900 --> 00:05:41,900 And so the most sensitive to its gravity, it was making images of 95 00:05:41,900 --> 00:05:45,100 the surface only when it was far away. 96 00:05:45,400 --> 00:05:47,700 Was it actually pointing back to the Earth. 97 00:05:48,200 --> 00:05:52,200 And so, I had this frustrating business for the first, 98 00:05:52,400 --> 00:05:55,100 something like two years and spacecraft. 99 00:05:55,100 --> 00:05:58,400 You didn't measure any gravity at all and that was very 100 00:05:58,400 --> 00:06:00,500 frustrating. I just had to live with this 101 00:06:00,500 --> 00:06:04,400 hoping that the spacecraft would not fail before. 102 00:06:04,400 --> 00:06:08,100 Actually, it could do something, which was my principal motive. 103 00:06:08,300 --> 00:06:11,100 For being involved, unfortunately, the Imaging 104 00:06:11,100 --> 00:06:14,400 failed, but we still have communications with it, so I 105 00:06:14,400 --> 00:06:15,200 was. Alright. 106 00:06:15,600 --> 00:06:17,600 So here we had a failure on the spacecraft. 107 00:06:17,600 --> 00:06:21,200 That actually was a good thing for you, save me, but then 108 00:06:21,200 --> 00:06:23,700 something else happened. It's of course, it costs 40 109 00:06:23,700 --> 00:06:27,100 million dollars a year to keep the spacecraft running. 110 00:06:27,500 --> 00:06:31,900 And once all the people who were making images of the surface 111 00:06:32,000 --> 00:06:37,100 when they're longer interested, then NASA of course its initial 112 00:06:37,100 --> 00:06:40,600 reaction was To shut the spacecraft down but we persuaded 113 00:06:40,600 --> 00:06:43,900 them not to at least for a couple of years and then they 114 00:06:43,900 --> 00:06:46,400 got finally. So frustrated, they used little 115 00:06:46,400 --> 00:06:49,800 bit of fuel that was left to actually put the spacecraft into 116 00:06:49,800 --> 00:06:53,000 Venus, right? Destroy it and that stopped all 117 00:06:53,000 --> 00:06:55,800 argument. How long did you actually have 118 00:06:55,800 --> 00:07:01,500 then to make these measurements it takes in ass about 250 days 119 00:07:01,700 --> 00:07:04,300 to rotate and the spacecraft will be. 120 00:07:04,300 --> 00:07:07,000 It doesn't rotate. So you get one. 121 00:07:07,000 --> 00:07:10,900 Look at Hope. About once every 250 days. 122 00:07:11,400 --> 00:07:15,900 So the mapping took or I think about two years and that after 123 00:07:15,900 --> 00:07:19,700 that we then got three Cycles looking at the gravity so it was 124 00:07:19,700 --> 00:07:22,300 a very slow business. So you said, you could measure 125 00:07:22,300 --> 00:07:26,200 the speed of the spacecraft to enormous accuracy, using the 126 00:07:26,200 --> 00:07:28,700 Doppler effect on the radio signal coming from the 127 00:07:28,700 --> 00:07:31,500 spacecraft. But how does that tell you what? 128 00:07:31,500 --> 00:07:34,800 The gravity field is does it speed up a bit when the gravity 129 00:07:34,800 --> 00:07:37,600 is a little bit stronger and slow down a bit when the gravity 130 00:07:37,600 --> 00:07:39,200 is a bit weak. Aker yes. 131 00:07:39,400 --> 00:07:42,200 The gravity field is just the accelerations and that's the 132 00:07:42,207 --> 00:07:45,400 gravity field at the satellite. So that's a straight measurement 133 00:07:45,400 --> 00:07:47,100 at the satellite. You just have to look at the 134 00:07:47,100 --> 00:07:49,800 rate at which the velocity changes and that's the gravity 135 00:07:49,800 --> 00:07:51,000 in the direction. You're looking. 136 00:07:51,400 --> 00:07:53,000 It's not the gravity at the surface. 137 00:07:53,000 --> 00:07:55,700 That's a more complicated thing is because it's a very 138 00:07:55,700 --> 00:07:58,200 straightforward measurement. Trust direct from the Doppler 139 00:07:58,200 --> 00:08:01,600 shift and that's what I actually use the Doppler shift itself. 140 00:08:02,600 --> 00:08:05,000 Okay, so you've got the gravity fluctuations. 141 00:08:05,000 --> 00:08:09,200 Now, what did that tell you? What I did was to look at the 142 00:08:09,200 --> 00:08:12,200 relationship between the gravity and the shape of the plant, 143 00:08:12,200 --> 00:08:15,500 that's about your fee. And what I was interested in was 144 00:08:15,700 --> 00:08:18,600 essentially, the thickness. What on Earth is the thickness 145 00:08:18,600 --> 00:08:22,500 of the plates in Venus, there's a layer which essentially quite 146 00:08:22,500 --> 00:08:26,700 strong and can support short, horizontal wavelength features. 147 00:08:27,000 --> 00:08:32,799 So small mountains, there are completely supported by this 148 00:08:32,799 --> 00:08:35,000 elastic layer. And when you look at the 149 00:08:35,000 --> 00:08:39,700 gravity, there's things you Just looking at the mass essentially 150 00:08:39,799 --> 00:08:43,200 that would be short wavelength features just to interjection 151 00:08:43,200 --> 00:08:47,300 explain a couple of things here. Short wavelength, now means 152 00:08:47,300 --> 00:08:50,300 special wavelength in other words, distance scales on the 153 00:08:50,300 --> 00:08:52,000 surface. Nothing to do with the 154 00:08:52,008 --> 00:08:55,200 wavelength of the Doppler signal that you're listening to and by 155 00:08:55,200 --> 00:08:58,500 elastic layer. You mean, even though it bends, 156 00:08:58,700 --> 00:09:02,800 it's a rigid layer as opposed to a mushy ductile layer. 157 00:09:03,000 --> 00:09:04,800 That wouldn't hold anything up at all. 158 00:09:05,200 --> 00:09:11,600 Yes, but Anyway, what we knew was that long wavelength 159 00:09:11,600 --> 00:09:15,800 features, like for instance, too bad, these are not supported 160 00:09:15,800 --> 00:09:19,400 elastically except at their edges May float. 161 00:09:19,400 --> 00:09:23,700 They're like icebergs floating in the mantle, the crust of the 162 00:09:23,700 --> 00:09:27,600 earth that partner we're used to has a lower density than the 163 00:09:27,600 --> 00:09:30,200 interior. So, if you have a thick layer of 164 00:09:30,200 --> 00:09:34,600 the crust, it essentially, floats in the material below. 165 00:09:34,900 --> 00:09:38,600 The gravity field from a floating object, It is nothing. 166 00:09:38,800 --> 00:09:43,200 So, the topography then, is what we call compensated, which means 167 00:09:43,200 --> 00:09:47,000 that it doesn't produce a gravity field and a changeover 168 00:09:47,000 --> 00:09:51,100 from things which do produce gravity field to things, which 169 00:09:51,100 --> 00:09:55,500 don't obviously tells you just like, you know, walking on ice. 170 00:09:55,800 --> 00:09:59,600 You can tell how thick the ice is by how much it bends that 171 00:09:59,600 --> 00:10:01,500 tells you the thickness of the elastic. 172 00:10:01,500 --> 00:10:03,600 Learn this is what we wanted to get at. 173 00:10:04,100 --> 00:10:07,500 What I wanted to look at was the relationship of the How do you 174 00:10:07,500 --> 00:10:11,700 feel to essentially the surface Topography of the planet? 175 00:10:12,000 --> 00:10:15,100 Also an iceberg. Marooned on a totally rigid 176 00:10:15,100 --> 00:10:18,300 plate and reaching the same height as the floating one. 177 00:10:18,900 --> 00:10:22,800 In other words, with identical, topography will increase the 178 00:10:22,800 --> 00:10:26,800 gravity because the whole of the iceberg is so to speak extra 179 00:10:26,800 --> 00:10:31,500 mass without any low density. Compensation below it and 180 00:10:31,500 --> 00:10:36,300 Venus's plate will be somewhere in between and we're in between 181 00:10:36,300 --> 00:10:38,600 it is Is what you're finding out. 182 00:10:39,100 --> 00:10:44,000 Yes, it's not quite as simple as that because there's also 183 00:10:44,300 --> 00:10:49,800 another effect, which is that on Earth, the mantle is is actually 184 00:10:49,800 --> 00:10:52,500 convicting, it's sufficiently fluid. 185 00:10:52,500 --> 00:10:55,800 Its viscosity is low enough. That actually, there are regions 186 00:10:55,800 --> 00:10:59,700 where the mantle is coming up and going down just like putting 187 00:10:59,700 --> 00:11:01,300 water in a saucepan and boiling, it. 188 00:11:01,700 --> 00:11:06,300 And that also produces a gravity field because it pushes the 189 00:11:06,300 --> 00:11:09,500 surface where it's Me up. It pushes the surface up when 190 00:11:09,500 --> 00:11:11,800 it's going down, it pushes the surface down. 191 00:11:12,200 --> 00:11:15,000 Let me try and explain how this affects the gravity field. 192 00:11:15,700 --> 00:11:19,000 If we think about a hot spot where the mantle is coming up, 193 00:11:19,400 --> 00:11:22,500 the density, there is less than its surroundings because of 194 00:11:22,500 --> 00:11:26,600 thermal expansion, that would have the effect of lowering the 195 00:11:26,600 --> 00:11:30,600 gravity field above it. But as you said, it also pushes 196 00:11:30,600 --> 00:11:33,600 up on the plate that lies above it, bending it. 197 00:11:33,600 --> 00:11:37,700 So it bulges upward and the extra material, In the Bulge 198 00:11:37,700 --> 00:11:41,600 increases the gravity. It turns out that this increase 199 00:11:41,600 --> 00:11:44,500 outweighs the decrease from the lower density of the material 200 00:11:44,500 --> 00:11:49,900 below with the net result that gravity increases by about a 201 00:11:49,900 --> 00:11:53,500 third of what we would expect from the effect of the surface 202 00:11:53,500 --> 00:11:57,300 bulge alone. So you have to have enough 203 00:11:57,300 --> 00:11:59,700 information to be able to distinguish between these two 204 00:11:59,700 --> 00:12:02,000 things. And the way in which you do that 205 00:12:02,000 --> 00:12:08,100 is that actually the signal, the amount of gravity you get Km of 206 00:12:08,100 --> 00:12:09,800 elevation is different in the two cases. 207 00:12:09,800 --> 00:12:15,300 So that was what I wanted to get at and that means essentially 208 00:12:15,300 --> 00:12:20,500 working over a range of wavelengths and seeing where 209 00:12:20,500 --> 00:12:24,800 changes from floating to being essentially supported 210 00:12:24,800 --> 00:12:29,600 elastically and that we could do and what we found, which 211 00:12:29,600 --> 00:12:33,900 surprised me very much actually when we found it was that the 212 00:12:33,900 --> 00:12:38,300 elastic layer on Venus is 230 kilometers. 213 00:12:38,600 --> 00:12:42,100 And that's the same as the thickness on Earth. 214 00:12:42,200 --> 00:12:45,600 But only the thickest part of things on Earth are the thickest 215 00:12:45,600 --> 00:12:49,400 part on Earth is old oceanic plates. 216 00:12:49,800 --> 00:12:53,700 And where the surface rocks are very old where there are more 217 00:12:53,700 --> 00:12:57,100 than a thousand million years old underneath those, the plates 218 00:12:57,100 --> 00:13:00,600 of called, they've got strong, they got elastic and they are 219 00:13:00,600 --> 00:13:06,200 also about 30 km thick, but the bottom of that layer, the 220 00:13:06,200 --> 00:13:08,400 thickness of the ice. They're governed by the 221 00:13:08,400 --> 00:13:12,800 temperature and the bottom of that left and both places is 222 00:13:12,800 --> 00:13:18,100 about 450 degrees Centigrade. The surface temperature of Venus 223 00:13:18,800 --> 00:13:23,800 is about 420 degrees, Centigrade so I not expected to see 224 00:13:23,900 --> 00:13:27,400 anything like that. I hadn't expected Venus have any 225 00:13:27,400 --> 00:13:29,900 strength at all. Expected us to be looking at the 226 00:13:29,900 --> 00:13:32,400 convective signal from the mantle convection. 227 00:13:32,400 --> 00:13:36,900 We could also see that clearly, but we could see both things but 228 00:13:36,900 --> 00:13:39,000 the The thing that really surprised me was how thick the 229 00:13:39,000 --> 00:13:41,800 elastic level. So you are thinking that because 230 00:13:41,800 --> 00:13:44,500 Venus was so hot, the Rocks had to be so weak. 231 00:13:44,800 --> 00:13:48,200 That really all the mountains would be sinking into the bottom 232 00:13:48,200 --> 00:13:51,400 and bit more like the floating icebergs situation or any rather 233 00:13:51,400 --> 00:13:55,100 than the rigid plate situation. Exactly. 234 00:13:55,300 --> 00:13:58,600 We had no previous knowledge, you can already tell. 235 00:13:58,600 --> 00:14:01,000 This, of course, if there are mountains on being as which is 236 00:14:01,000 --> 00:14:04,700 supported by the convection, you really need both the topography 237 00:14:04,700 --> 00:14:06,800 and the gravity before you can tell. 238 00:14:07,200 --> 00:14:10,100 That being pushed down by convective, circulation 239 00:14:10,100 --> 00:14:13,000 underneath, or whether they're supported elastic key. 240 00:14:13,200 --> 00:14:16,800 And once we got the gravity, we could see that very clearly. 241 00:14:17,300 --> 00:14:20,000 So, how can such incredibly hot rocks? 242 00:14:20,000 --> 00:14:24,800 Be so strong on Venus, that was the great surprise. 243 00:14:24,800 --> 00:14:29,500 And that course, particularly David coasted in Minnesota. 244 00:14:30,700 --> 00:14:35,500 To look at the role of water. We knew that quite small amounts 245 00:14:35,500 --> 00:14:38,200 of water in rocks, made them week. 246 00:14:38,900 --> 00:14:42,100 But what he found was that really quite minut. 247 00:14:42,100 --> 00:14:46,700 Amounts of water were important, just simply transferring the 248 00:14:46,700 --> 00:14:49,800 samples. He was going to test from the 249 00:14:49,800 --> 00:14:54,200 oven in which they were dried to The Apparition which was going 250 00:14:54,200 --> 00:14:56,900 to test. They absorbed enough water from 251 00:14:56,900 --> 00:15:00,000 the atmosphere just on that transfer. 252 00:15:00,500 --> 00:15:04,000 To change their properties. And this we had really no idea 253 00:15:04,000 --> 00:15:08,400 about before Venus. We know that the Earth has got 254 00:15:08,900 --> 00:15:14,200 about 100 parts per million of water in the mantle and Dave 255 00:15:14,200 --> 00:15:16,600 because it experiments particularly show that this is 256 00:15:16,600 --> 00:15:21,500 quite enough to make it soft and really very soft whereas Venus 257 00:15:21,800 --> 00:15:26,600 because it's extremely hot and also its atmosphere is extremely 258 00:15:26,600 --> 00:15:30,300 dry if you would condense all the water in Venus's atmosphere, 259 00:15:30,400 --> 00:15:34,500 The sphere onto the surface, you get oceans, which about 10 cm 260 00:15:34,500 --> 00:15:37,400 thick. It's really as dry as a bone and 261 00:15:37,400 --> 00:15:40,800 it's very hot. So it's like they've caused it's 262 00:15:40,800 --> 00:15:46,100 often and that affects both the elastic properties and also the 263 00:15:46,100 --> 00:15:51,500 viscosity of the correcting mantle and that then really 264 00:15:51,600 --> 00:15:54,600 solve the problem. But we had previously really no 265 00:15:54,600 --> 00:16:00,000 idea that is very small amount of water on Earth in the mantle 266 00:16:00,100 --> 00:16:02,800 play. Important role particularly in 267 00:16:02,800 --> 00:16:05,900 plate tectonics. Then when we looked at Venus 268 00:16:06,200 --> 00:16:11,300 most of the planet is absolutely not like the Earth. 269 00:16:11,300 --> 00:16:14,300 It is not covered with moving plates. 270 00:16:15,000 --> 00:16:19,300 There are a few places on the planet, which do look quite like 271 00:16:19,300 --> 00:16:22,900 some of the features on plate boundaries, but most of the 272 00:16:22,900 --> 00:16:25,900 planet is not like that at all. It's just covered with lava 273 00:16:25,900 --> 00:16:27,900 flows. It's essentially a one plate 274 00:16:27,900 --> 00:16:30,600 planet. Now, as far as we can tell, Ow. 275 00:16:31,200 --> 00:16:34,500 And for me a justification for looking at another planet, we 276 00:16:34,500 --> 00:16:38,000 had no idea that water was so important. 277 00:16:38,600 --> 00:16:42,700 That's fascinating that by looking at Venus and seeing how 278 00:16:42,900 --> 00:16:46,200 dry it was and how different it behave from the earth that 279 00:16:46,600 --> 00:16:49,700 really made us look again at the importance of water on Mars, 280 00:16:49,700 --> 00:16:52,900 even though we already knew how much water there was in the 281 00:16:52,900 --> 00:16:55,500 rocks on Earth, we just didn't understand its significance. 282 00:16:56,200 --> 00:16:59,700 We hadn't really thought that such small amounts of water 283 00:16:59,700 --> 00:17:03,100 could matter. Or that the experiments that we 284 00:17:03,100 --> 00:17:07,000 were doing, which we thought were dry, not actually, as dry, 285 00:17:07,000 --> 00:17:10,000 as we thought they were this mattered. 286 00:17:10,300 --> 00:17:16,000 I mean, yeah, it's a very nice illustration of how you need 287 00:17:16,200 --> 00:17:20,700 both the observations from The Real World. 288 00:17:20,700 --> 00:17:24,000 And also, then to do lab experiments properly, control 289 00:17:24,000 --> 00:17:26,200 lab experiments to see what's going on. 290 00:17:26,599 --> 00:17:29,800 And that was really, a very nice illustration of the importance 291 00:17:29,800 --> 00:17:32,300 of both. 'The, I'm struck that since you 292 00:17:32,300 --> 00:17:35,400 found out that even a tiny amount of water can make rock 293 00:17:35,400 --> 00:17:37,800 softer. It's all the more surprising 294 00:17:37,800 --> 00:17:41,200 that on Earth, the spherical caps, which you referred to 295 00:17:41,200 --> 00:17:46,300 earlier, which can be 10,000 km wide move about as rigid plates. 296 00:17:46,800 --> 00:17:52,200 Well, yeah, that was why they took such a long time for 297 00:17:52,200 --> 00:17:55,500 Georgia's to recognize, but plate motions on Earth. 298 00:17:55,800 --> 00:18:00,000 And I mean, this, this sort of behavior is really only true for 299 00:18:00,000 --> 00:18:02,600 the As she anak awesome. The plates conscience. 300 00:18:02,600 --> 00:18:05,600 Deform like entering and much more distributed. 301 00:18:05,700 --> 00:18:08,900 If you look at a map of earthquakes from Northern India 302 00:18:09,600 --> 00:18:13,200 2000 km North from the whole of that region is deforming. 303 00:18:13,800 --> 00:18:16,600 And in the oceans that's absolutely not the case. 304 00:18:16,600 --> 00:18:18,800 The plate. Boundary beneath Japan is really 305 00:18:18,800 --> 00:18:21,000 sharp. It's just one big fault which 306 00:18:21,000 --> 00:18:23,300 moves in the Japanese earthquake. 307 00:18:23,400 --> 00:18:26,900 It moves, 70 meters. Now the really isn't anything 308 00:18:26,900 --> 00:18:30,200 like that on the continents. It was really only there. 309 00:18:30,300 --> 00:18:34,000 Suppression of the oceans, which showed what was going on. 310 00:18:34,000 --> 00:18:37,500 And once we had a good understanding of that, we then 311 00:18:37,500 --> 00:18:40,400 could go back to the contents and see what was going on. 312 00:18:40,600 --> 00:18:43,600 And of course, GPS, we knew what was going on really from 313 00:18:43,600 --> 00:18:48,400 earthquake and from magnetic anomalies in the oceans but any 314 00:18:48,400 --> 00:18:51,300 remaining doubts were completely squashed by the GPS 315 00:18:51,300 --> 00:18:55,300 measurements, much easier to do GPS on land, and it's just to do 316 00:18:55,300 --> 00:18:58,900 it at Sea and that's being done all over the world's continents 317 00:18:58,900 --> 00:19:01,700 and confirmed. Absolutely everything that we 318 00:19:01,700 --> 00:19:05,300 thought was the case from the earthquakes for my last 319 00:19:05,300 --> 00:19:07,000 question. I want to come back to your 320 00:19:07,000 --> 00:19:10,100 point that we had to look at another planet to get a better 321 00:19:10,100 --> 00:19:13,700 perspective on our own and the fact that we're advancing by 322 00:19:13,700 --> 00:19:16,800 Leaps and Bounds. Now in our ability to look at 323 00:19:16,800 --> 00:19:21,100 planets around other stars, in fact we found over 4,000 of them 324 00:19:21,100 --> 00:19:22,700 and the numbers increasing rapidly. 325 00:19:23,700 --> 00:19:25,700 I'm wondering if you think that's going to help us 326 00:19:25,700 --> 00:19:28,800 understand more about the Earth and how it got to be where it is 327 00:19:28,800 --> 00:19:31,200 in our solar system. I'm sure. 328 00:19:31,300 --> 00:19:35,500 Well up until discovery of all these exoplanets, we only really 329 00:19:35,500 --> 00:19:40,700 had one solar system to look at. And furthermore, the things that 330 00:19:40,700 --> 00:19:43,700 happened which formed it happened. 331 00:19:43,700 --> 00:19:47,600 Four and a half thousand million years ago and the events are 332 00:19:47,600 --> 00:19:50,300 clearly very strange. There's a lot of very odd 333 00:19:50,300 --> 00:19:52,600 things. One of the ones which is very 334 00:19:52,600 --> 00:19:56,200 simple State is a lot of meteorites, the rocky 335 00:19:56,200 --> 00:20:02,200 meteorites, contain these small spheres of rock which is 336 00:20:02,400 --> 00:20:06,600 actually mostly Olivine, which is the same composition as the 337 00:20:06,600 --> 00:20:09,300 Earth and these things have obviously been molten. 338 00:20:10,100 --> 00:20:13,400 That's very cool because of surface tension, they're all 339 00:20:13,400 --> 00:20:15,500 mixed up. There are some extremely high 340 00:20:15,500 --> 00:20:19,200 temperature once a much lower temperature ones and the Matrix, 341 00:20:19,400 --> 00:20:23,800 a lot of it is Clay. Its it contains water so So how 342 00:20:23,800 --> 00:20:26,800 in the world are these things formed and how they put 343 00:20:26,800 --> 00:20:29,300 together, the composition of the earth. 344 00:20:29,400 --> 00:20:35,300 Looks like essentially one set of these meteorites and we have 345 00:20:35,300 --> 00:20:38,600 a whole lot of really, quite speculative theories about this 346 00:20:38,900 --> 00:20:43,400 but we've daily, don't know. And that the whole process is go 347 00:20:43,400 --> 00:20:47,600 on as a star forms, rather hard to image. 348 00:20:47,600 --> 00:20:52,400 That is a long way away in clouds of dust and they form a 349 00:20:52,408 --> 00:20:54,600 great variety. Of different sizes. 350 00:20:54,600 --> 00:20:58,500 And during the formation of these stars and their planetary 351 00:20:58,500 --> 00:21:03,800 systems, the big ones evolved very fast explode and do a lot 352 00:21:03,800 --> 00:21:07,500 of radioactive material, which we can see in the meteorites 353 00:21:07,500 --> 00:21:11,700 that when they were formed, certain of the elements were 354 00:21:11,700 --> 00:21:14,500 extremely radioactive and then they decayed. 355 00:21:15,100 --> 00:21:20,100 We only really understood that once we saw how stars, formed in 356 00:21:20,100 --> 00:21:24,300 these clouds, and I'm quite sure the same scheme to Be true of 357 00:21:24,300 --> 00:21:28,000 all the rest of how the solar system was put together once we 358 00:21:28,000 --> 00:21:32,600 can image these remote ones that we've now discovered. 359 00:21:32,900 --> 00:21:35,800 But yeah, technology is marvelous. 360 00:21:35,900 --> 00:21:41,300 It just Marches On and all kinds of things will become possible 361 00:21:41,500 --> 00:21:45,100 in the not very distant future and I'm quite sure there are 362 00:21:45,100 --> 00:21:47,400 lots of them. We're going to find some, which 363 00:21:47,400 --> 00:21:51,600 are forming now and that will be an enormous help to 364 00:21:51,600 --> 00:21:56,600 understanding how Solar system got put together because the 365 00:21:56,600 --> 00:22:00,900 problem is we don't even know how common solar system like 366 00:22:00,900 --> 00:22:04,300 ours is because we live on this one. 367 00:22:04,900 --> 00:22:09,100 We know that we need water to live and all the rest of it. 368 00:22:09,600 --> 00:22:12,500 How common is that? We don't know if it wasn't like 369 00:22:12,500 --> 00:22:16,300 that, we wouldn't be here to look be looking at it so that 370 00:22:16,300 --> 00:22:19,900 extremely difficult to know how to attack problems and this 371 00:22:20,300 --> 00:22:23,700 especially when there is complicated as this and one of 372 00:22:23,700 --> 00:22:28,100 the things which has really come from looking at the planets of 373 00:22:28,300 --> 00:22:30,800 this solar system is particularly come from their 374 00:22:30,800 --> 00:22:34,400 satellites and they're all different. 375 00:22:34,500 --> 00:22:39,500 They just extraordinary variety and quite astonishing that they 376 00:22:39,500 --> 00:22:41,800 look as different as they are. We don't know much about the 377 00:22:41,800 --> 00:22:46,000 insides yet most of them anyway but they are quite different 378 00:22:46,000 --> 00:22:49,400 from each other and so presumably the same is going to 379 00:22:49,400 --> 00:22:52,700 be true of solar systems that they're going to be completely 380 00:22:52,700 --> 00:22:54,300 variable. Not set me. 381 00:22:54,300 --> 00:22:57,300 What's coming out from the little bit of knowledge that we 382 00:22:57,300 --> 00:22:59,900 have of them so far. Definitely going to do another 383 00:22:59,900 --> 00:23:01,800 podcast with you. When we have enough data on 384 00:23:01,800 --> 00:23:04,100 these new solar systems will be dead. 385 00:23:08,400 --> 00:23:10,700 Dan Mackenzie. Thank you very much. 386 00:23:11,000 --> 00:23:11,500 Good.