WEBVTT - What's hidden inside planets? 0:00:08.640 --> 0:00:11.560 When we set out to understand the universe, we usually 0:00:11.600 --> 0:00:14.760 start by looking up. After all, that's where the best 0:00:14.880 --> 0:00:18.880 views are of the glittery cosmos stretched across billions of miles. 0:00:19.440 --> 0:00:22.560 We wonder, are we alone? Is there anyone up there 0:00:22.680 --> 0:00:25.160 looking back at us? But what if the best way 0:00:25.200 --> 0:00:28.640 to find answers to questions about what's up there is 0:00:28.720 --> 0:00:47.920 actually to look down under our feet. Hi, I'm Daniel. 0:00:47.960 --> 0:00:51.280 I'm a particle physicist and a professor at UC Irvine, 0:00:51.440 --> 0:00:53.880 and I desperately want to know who's out there in 0:00:53.920 --> 0:00:57.000 the universe and if they are wondering the same things 0:00:57.200 --> 0:00:59.960 we are. And Welcome to the podcast Daniel and Horace 0:01:00.320 --> 0:01:03.720 Explain the Universe in which we do just that, wonder 0:01:03.760 --> 0:01:06.000 about the nature of the universe and try to explain 0:01:06.200 --> 0:01:09.480 all of it to you. Regular listeners the podcast, know 0:01:09.520 --> 0:01:12.959 that I am desperate to understand the nature of the universe, 0:01:13.240 --> 0:01:15.680 how it all works, and to explain all of that 0:01:15.760 --> 0:01:18.560 knowledge and all of that confusion to you. One of 0:01:18.600 --> 0:01:20.959 the deepest questions we wrestle with on the pod is 0:01:21.000 --> 0:01:24.320 not just about the universe, but kind of about ourselves. 0:01:24.959 --> 0:01:28.400 How weird? Are we are? There more like us out 0:01:28.400 --> 0:01:32.119 there in the universe, or are we alone? How rare 0:01:32.280 --> 0:01:35.920 and special is the Earth anyway? Are we one of 0:01:35.959 --> 0:01:38.800 a kind out of a trillion planets, or are we 0:01:38.840 --> 0:01:42.320 one of many rocky balls covered in Curious Life. We're 0:01:42.319 --> 0:01:46.120 frustratingly limited by what we can learn about distant planets, 0:01:46.160 --> 0:01:49.200 though we're doing our best. But something we can do 0:01:49.480 --> 0:01:53.600 right now is drill deeper into our own planet, understand 0:01:53.640 --> 0:01:56.400 the forces that shaped it and whether those are finely 0:01:56.440 --> 0:02:00.120 balanced in a rare way or naturally in harmony, in 0:02:00.120 --> 0:02:02.880 a way we'll find everywhere in the universe. So today 0:02:02.880 --> 0:02:10.840 on the podcast, we'll be answering the question what's hidden 0:02:11.200 --> 0:02:15.120 inside planets? And to help me explore this fascinating topic, 0:02:15.200 --> 0:02:18.480 I'm pleasing to be speaking to Professor Sabina Stanley, author 0:02:18.520 --> 0:02:26.160 of a very recent book of that same title. All right, well, 0:02:26.160 --> 0:02:29.040 then it's my great pleasure to introduce the podcast Professor 0:02:29.040 --> 0:02:32.840 Sabina Stanley. She's the Bloomberg Distinguished Professor of Planetary Physics 0:02:32.840 --> 0:02:35.720 at Johns Hopkins University, where she focuses on magnetic fields 0:02:35.720 --> 0:02:38.359 and other geophysical elements as a means of studying the 0:02:38.400 --> 0:02:42.960 interiors of planets, moons, and asteroids. She's an Alfred Peasloan 0:02:43.080 --> 0:02:46.120 Research Fellow, and has also received the William Gilbert Award 0:02:46.160 --> 0:02:49.639 of the American Geophysical Union. Sabina, Welcome to the podcast, 0:02:49.639 --> 0:02:51.000 and thank you for coming to talk to us. 0:02:51.160 --> 0:02:52.240 Thanks so much for having me. 0:02:52.480 --> 0:02:54.600 So one thing we always wonder about as we look 0:02:54.680 --> 0:02:57.680 out into the night sky is all the other planets 0:02:57.720 --> 0:03:00.000 that are out there. Of course we can't study mnie 0:03:00.160 --> 0:03:03.320 them up close, and so often on this podcast we've 0:03:03.360 --> 0:03:06.239 tried to dig into what's under our feet, the mysteries 0:03:06.240 --> 0:03:08.440 that are right here in our Earth. And so I 0:03:08.560 --> 0:03:11.840 really enjoyed your recent book, What's Hidden Inside Planets, and 0:03:11.880 --> 0:03:14.720 I'd love to talk to you about what's in our planet. 0:03:15.080 --> 0:03:16.760 Could you start us off by taking us sort of 0:03:16.760 --> 0:03:19.440 on a brief tour of like what is under our feet, 0:03:19.760 --> 0:03:21.800 layer by layer, all the way down to the core. 0:03:22.160 --> 0:03:23.680 Yeah, absolutely, great question. 0:03:24.080 --> 0:03:26.440 So I think it's interesting to note that when you 0:03:26.480 --> 0:03:29.320 start on the surface, as you go deeper and deeper, 0:03:29.360 --> 0:03:32.160 stuff gets kind of weirder and weirder and much more 0:03:32.200 --> 0:03:33.840 different than what we're used to on the surface. 0:03:33.919 --> 0:03:35.400 So we start on the crust. 0:03:35.440 --> 0:03:37.040 This is where we live, This is where all the 0:03:37.080 --> 0:03:39.880 stuff happens that we're used to crust can vary in 0:03:39.960 --> 0:03:44.240 thickness five about you know, five kilometers depth to almost 0:03:44.240 --> 0:03:46.680 one hundred kilometers depth. But under that you get to 0:03:46.720 --> 0:03:50.560 the mantle that's also still mostly rocky, the type of 0:03:50.680 --> 0:03:53.400 rocks that are rich in magnesium and silicates, but still 0:03:53.400 --> 0:03:56.200 what we would recognize as rocks. So about half the 0:03:56.280 --> 0:03:58.440 radius of the Earth are those rocks. It goes down 0:03:58.440 --> 0:03:59.880 about two thousand miles deep. 0:04:00.080 --> 0:04:02.920 So what distinguishes then between the crust and the mantle. 0:04:03.000 --> 0:04:04.960 Is it like how squeezed they are and how much 0:04:05.000 --> 0:04:06.720 they flow, or is it a different kind of rock? 0:04:06.920 --> 0:04:07.560 Great question. 0:04:07.640 --> 0:04:09.640 Yeah, it's a little bit different kind of rock. So 0:04:09.800 --> 0:04:13.520 essentially the crust layer of the earth. I sometimes refer 0:04:13.600 --> 0:04:15.320 to it as like the scum of the earth. So 0:04:15.320 --> 0:04:16.640 it's kind of like, you know, like when you're making 0:04:16.680 --> 0:04:20.000 a soup and you're boiling your broth and you've got 0:04:20.040 --> 0:04:21.960 all that light, floaty stuff that comes to the top. 0:04:22.000 --> 0:04:24.520 So the stuff that's the most buoyant when you have 0:04:24.640 --> 0:04:28.440 certain heat, thermal reactions and chemical reactions happening with rocks 0:04:28.480 --> 0:04:31.000 near the surface, all of that percolates up to the 0:04:31.000 --> 0:04:33.280 top and that ends up becoming the crust, and then 0:04:33.360 --> 0:04:36.920 sort of the stuff underneath might be less scummy, less 0:04:37.160 --> 0:04:39.479 you know, it's been less reworked, and it's sort of 0:04:39.520 --> 0:04:41.160 more kind of pristine rock. 0:04:41.320 --> 0:04:43.200 I see, we're going to get started very quickly with 0:04:43.240 --> 0:04:44.200 the food analogies. 0:04:44.400 --> 0:04:46.680 Yeah, I'm sorry, it's just going to be how it goes. 0:04:46.720 --> 0:04:48.880 It's going to be food involved in almost every analogy 0:04:49.080 --> 0:04:49.440 I make. 0:04:49.480 --> 0:04:49.720 Here. 0:04:49.920 --> 0:04:51.520 Are you a big fan of soup or you a 0:04:51.520 --> 0:04:52.120 cook at home? 0:04:52.640 --> 0:04:55.039 So I'm a terrible cook, but I grew up in 0:04:55.080 --> 0:04:57.480 a restaurant family, so I've been around sort of good 0:04:57.480 --> 0:04:58.520 food my whole life. 0:04:58.640 --> 0:05:00.560 All right, Well, then let's do our best to at 0:05:00.640 --> 0:05:03.200 least use tasty food analogies. I don't want any want 0:05:03.279 --> 0:05:05.360 to think that the earth is like a disgusting bowl 0:05:05.360 --> 0:05:07.640 of soup. Maybe it's like, you know, bubbling hot cocoa, 0:05:07.680 --> 0:05:10.240 and this is that delicious film that forms on top. 0:05:10.520 --> 0:05:12.279 I love that so much. You don't even know. So 0:05:12.360 --> 0:05:13.760 that's amazing, all right. 0:05:13.800 --> 0:05:16.360 So the crust is the sort of coolest part that 0:05:16.400 --> 0:05:18.680 floats to the top, and underneath that it's still rock, 0:05:18.920 --> 0:05:21.719 but it's able to flow. How do we visualize that? 0:05:21.800 --> 0:05:24.440 I mean, it's not like liquid lava that's flowing on 0:05:24.480 --> 0:05:27.640 the surface. This is still like solid rock, but it's flowing. 0:05:27.680 --> 0:05:30.640 How does solid rock flow is something I've always tried 0:05:30.640 --> 0:05:31.919 to visualize and failed. 0:05:32.120 --> 0:05:34.800 Yeah, So the answer to that question is very slowly. 0:05:35.360 --> 0:05:35.600 Right. 0:05:35.680 --> 0:05:39.640 So, yes, it's solid, but it's still deformable, right, And 0:05:39.680 --> 0:05:42.440 I think we have experience with different types of solids 0:05:42.480 --> 0:05:44.800 in our everyday life, and that some are more deformable 0:05:44.800 --> 0:05:45.120 than other. 0:05:45.200 --> 0:05:46.239 Right, Like you might have clay. 0:05:46.480 --> 0:05:48.960 Clay is solid, but you can still deform it, whereas 0:05:49.080 --> 0:05:51.440 a metal also is kind of deformable. But then you 0:05:51.440 --> 0:05:53.440 have some rocks that are really like a diamond, really 0:05:53.480 --> 0:05:55.600 hard to deform. But the rocks in the mantle, they 0:05:55.640 --> 0:05:57.920 are solid, but they can be deformed, and if they 0:05:57.920 --> 0:06:00.960 can be deformed, then they start being influenced by the 0:06:01.000 --> 0:06:04.800 forces like gravity such that you can get them to flow. 0:06:05.200 --> 0:06:07.359 I see, all right, So we have the crust and 0:06:07.400 --> 0:06:09.400 we have the mantle. Both the wiz are still really rock. 0:06:09.600 --> 0:06:11.080 Take us down below that, right. 0:06:10.960 --> 0:06:12.880 So then you get down about halfway through the Earth 0:06:12.920 --> 0:06:16.279 and you suddenly hit a very big boundary, complete change 0:06:16.279 --> 0:06:20.800 of environment. Now you're at the iron core. So the 0:06:20.839 --> 0:06:23.839 inner half of the planet about it's mostly made of iron. 0:06:24.000 --> 0:06:26.240 There's a little bit of nickel mixed in there, and 0:06:26.320 --> 0:06:29.760 about ten percent of some sort of lighter elements that 0:06:30.080 --> 0:06:32.720 we have a whole sort of platter of possibilities for, 0:06:32.880 --> 0:06:35.040 but we don't actually know what they are. And that 0:06:35.080 --> 0:06:37.600 makes up the core. The core has two parts to it. 0:06:37.960 --> 0:06:40.919 The outer port is liquid. It can flow very easily, 0:06:41.040 --> 0:06:44.920 much faster timescales than the mantle, and it's really important 0:06:44.920 --> 0:06:47.120 for us because that's where our magnetic field is generated 0:06:47.120 --> 0:06:50.920 in that liquid iron core. Then below that, the innermost 0:06:51.040 --> 0:06:54.360 thirteen hundred kilometers of our planet, is a solid iron core. 0:06:54.520 --> 0:06:57.680 And so what distinguishes then the mantle, which can flow 0:06:57.839 --> 0:07:00.719 but is a solid not a liquid, from the outer core, 0:07:00.880 --> 0:07:04.279 which can flow but is a liquid and not a solid, Like, 0:07:04.440 --> 0:07:06.359 is there really a distinction here? Are we just putting 0:07:06.400 --> 0:07:07.240 labels on things? 0:07:07.400 --> 0:07:09.760 When we study fluid dynamics, we talk a lot about 0:07:09.760 --> 0:07:12.800 there being a spectrum of fluids. Right, nothing's ever purely 0:07:12.840 --> 0:07:15.040 a solid or purely a fluid. It's all about the 0:07:15.080 --> 0:07:18.480 time scales. So the mantle, for example, if you want 0:07:18.520 --> 0:07:21.520 to talk about how materials flow in the mantle, a 0:07:21.600 --> 0:07:23.680 parcel at the bottom of the mantle could take hundreds 0:07:23.720 --> 0:07:25.520 of millions of years to make it to the top 0:07:25.560 --> 0:07:27.760 of the mantle, whereas a parcel at the bottom of 0:07:27.800 --> 0:07:30.240 the core could take a couple of years to get 0:07:30.280 --> 0:07:31.960 the top of the core. So it's a very different 0:07:32.000 --> 0:07:35.160 timescale of the flow. You could actually see changes in 0:07:35.240 --> 0:07:37.320 material in the core flowing. 0:07:37.640 --> 0:07:39.600 But this is also like a boundary. It's not like 0:07:39.600 --> 0:07:43.000 there's a smooth, very gradual transition. There's like a line. 0:07:43.000 --> 0:07:44.800 You can say, this is the core and this is 0:07:44.840 --> 0:07:45.320 the mantle. 0:07:45.600 --> 0:07:48.920 Yeah, And that happens because mantle, rocks, and iron in 0:07:48.960 --> 0:07:52.160 the core have very different densities, and at one time 0:07:52.200 --> 0:07:55.000 in the past in our planet, it was mostly molten 0:07:55.400 --> 0:07:57.680 and so the heaviest stuff, when you have a bunch 0:07:57.720 --> 0:07:59.800 of stuff mixed together, the heaviest stuff's going to sync 0:07:59.840 --> 0:08:02.400 to the bottom. And so that's what happened in Earth. 0:08:02.600 --> 0:08:04.760 All the iron, most of the irons, sunk to the 0:08:04.760 --> 0:08:06.400 center of the Earth and made. 0:08:06.280 --> 0:08:08.600 Up the core like the big chunks in a stew 0:08:08.680 --> 0:08:09.920 or something exactly. 0:08:10.000 --> 0:08:10.680 Yes, I like it. 0:08:10.800 --> 0:08:12.720 So the reason that there's a boundary there and like 0:08:12.720 --> 0:08:15.200 a transition or rather than just like a smooth gradation 0:08:15.640 --> 0:08:18.240 from more liquid to less liquid, that reflects like the 0:08:18.240 --> 0:08:20.760 phase transitions and materials. Is that right, the way that 0:08:20.840 --> 0:08:23.840 like ice turns solid at some moment and doesn't just 0:08:23.840 --> 0:08:26.400 like gradually become more and more solid. 0:08:26.640 --> 0:08:28.840 I would say that's more representative of what kind of 0:08:28.840 --> 0:08:31.080 happens at the inner core outer core boundary, so where 0:08:31.120 --> 0:08:33.480 the iron becomes solid. But above that it's more kind 0:08:33.480 --> 0:08:36.120 of like a maybe you go with an oil and 0:08:36.280 --> 0:08:39.040 water type thing. You've got two materials with very different 0:08:39.080 --> 0:08:41.560 density and very different properties, so it's really hard to 0:08:41.600 --> 0:08:42.040 mix them. 0:08:42.360 --> 0:08:45.559 Wonderful and tell us about how we know about this. 0:08:45.920 --> 0:08:48.840 I was reading in your book this really exciting description 0:08:49.160 --> 0:08:52.000 of the mantle race, basically like a parallel to the 0:08:52.040 --> 0:08:54.840 space race, but into the Earth. Tell us about our 0:08:54.920 --> 0:08:57.599 humanity's efforts to like literally tunnel to the center of 0:08:57.640 --> 0:08:58.000 the Earth. 0:08:58.240 --> 0:09:00.640 Yeah, So if you imagine you want to figure what's 0:09:00.679 --> 0:09:03.200 inside the Earth, right, your first instinct might be, hey, 0:09:03.280 --> 0:09:05.120 why don't we dig down as far as we can 0:09:05.160 --> 0:09:06.120 and actually sample it? 0:09:06.200 --> 0:09:06.320 Right? 0:09:06.360 --> 0:09:09.920 And it's a great instinct. Unfortunately, it's incredibly challenging to do. 0:09:10.520 --> 0:09:13.960 And that's because pressure increases so fast as you go 0:09:14.040 --> 0:09:16.720 deeper inside the planet, and so do temperatures. So as 0:09:16.760 --> 0:09:20.119 you can imagine, humans don't like really high pressures and temperatures. 0:09:20.200 --> 0:09:23.160 Neither does equipment, and the farthest we've been able to 0:09:23.200 --> 0:09:26.640 dig with sort of a really concerted effort to do so, right, 0:09:26.679 --> 0:09:29.760 Like this was something on the scale of moonshot to 0:09:29.840 --> 0:09:32.760 the Moon in the late sixties. This is something very 0:09:32.760 --> 0:09:34.760 similar to that, And you could get only down to 0:09:34.800 --> 0:09:37.000 about eight miles in depth, and the radius of the 0:09:37.000 --> 0:09:40.080 Earth you're talking about four thousand miles, so tiny, tiny 0:09:40.120 --> 0:09:42.680 scrape of the surface by going down that deep. Equipment 0:09:42.720 --> 0:09:44.200 does not like high pressures and temperatures. 0:09:44.280 --> 0:09:46.640 But how do you even get eight miles deep? I mean, 0:09:46.679 --> 0:09:50.120 I remember digging in my backyard with a shovel, wondering 0:09:50.120 --> 0:09:51.920 how far I could get, and it's not very far. 0:09:52.400 --> 0:09:53.760 How do you get eight miles down? 0:09:54.000 --> 0:09:58.880 This is like high tech technology kind of stuff. It's 0:09:58.880 --> 0:10:00.760 at the limits of what we can do for drilling 0:10:01.760 --> 0:10:04.959 that we do now to drill for resources, et cetera. 0:10:05.080 --> 0:10:07.960 So it's a lot of fancy equipment and challenges that 0:10:08.000 --> 0:10:10.000 are over met that way. So we can't dig and 0:10:10.040 --> 0:10:13.280 we can't drill, But that's okay because there are other 0:10:13.320 --> 0:10:15.480 ways we can figure out what's going on deeper inside 0:10:15.480 --> 0:10:15.800 the earth. 0:10:16.000 --> 0:10:17.600 Yeah, So tell us about some of those ways you 0:10:17.640 --> 0:10:20.160 were talking in the book about diamonds, how we can 0:10:20.240 --> 0:10:23.080 use diamonds to give us little snapshots of what's inside 0:10:23.080 --> 0:10:23.520 the planet. 0:10:23.800 --> 0:10:25.559 Yeah, so you know, it would be great if we 0:10:25.559 --> 0:10:27.720 could dig down, but would it also be great if 0:10:27.760 --> 0:10:30.520 the stuff down there came to us. And that's really 0:10:30.520 --> 0:10:34.240 what happens with diamonds. Diamonds are produced deeper inside the Earth, 0:10:34.400 --> 0:10:36.679 and then they come up to the surface, usually in 0:10:36.960 --> 0:10:41.120 volcanic vent things known as kimber like pipes and those diamonds. 0:10:41.120 --> 0:10:43.960 You know, Jewelers love diamonds when they're as pure as possible. 0:10:44.160 --> 0:10:47.520 Geologists love diamonds when they're as impure as possible. So 0:10:48.040 --> 0:10:51.000 sometimes diamonds, when they form, they can enclose a little 0:10:51.040 --> 0:10:54.360 capsule of some of the material where they formed inside them, right, 0:10:54.400 --> 0:10:56.080 So you might get a little bit of garnet in 0:10:56.120 --> 0:10:57.880 the diamond or a little bit of something that was 0:10:57.920 --> 0:11:00.360 created deeper in the earth. And when it it up, 0:11:00.360 --> 0:11:03.160 because diamonds so strong, it actually keeps the material in 0:11:03.200 --> 0:11:06.040 its like pristine form, So you really have this like 0:11:06.160 --> 0:11:08.040 sample from the interior of the Earth come to the 0:11:08.080 --> 0:11:10.880 surface for us to investigate. So that's a great way 0:11:10.920 --> 0:11:12.959 and we've used that, for example, to figure out that 0:11:13.280 --> 0:11:16.880 there is actually water deeper inside the Earth because we've 0:11:16.920 --> 0:11:20.120 found water inside diamond inclusions. 0:11:20.360 --> 0:11:22.480 It's fascinating to me though, that this thing that you 0:11:22.559 --> 0:11:24.600 make in a high pressure environment, when you bring it 0:11:24.720 --> 0:11:28.120 up to low pressure, it doesn't explode. Is that just 0:11:28.120 --> 0:11:29.840 because of the incredible structure of diamond? 0:11:30.120 --> 0:11:30.400 Yeah. 0:11:30.480 --> 0:11:33.000 When they say diamonds are forever, that's technically not true, right, 0:11:33.000 --> 0:11:36.079 They just have a really really long lifetime before they 0:11:36.200 --> 0:11:37.720 revert back to their carbon phase. 0:11:37.800 --> 0:11:40.199 So yeah, it's just a great property of diamond. 0:11:40.320 --> 0:11:41.640 So is it's sort of like you know, you put 0:11:41.640 --> 0:11:44.000 a pan of brownies in the oven and it changes 0:11:44.040 --> 0:11:45.720 into something else, and when you take it out, cool 0:11:45.760 --> 0:11:47.520 it down, it doesn't revert back into batter. 0:11:47.880 --> 0:11:49.480 That's an excellent way of thinking about it. 0:11:49.559 --> 0:11:53.080 Yeah, okay, And so then what have we learned from 0:11:53.120 --> 0:11:56.440 these diamond samples? Like what's inside these diamonds that we 0:11:56.480 --> 0:11:57.959 didn't realize other than water? 0:11:58.120 --> 0:11:59.960 Yeah? I think water is the big thing. 0:12:00.120 --> 0:12:04.240 Sometimes it's a lot about sort of the smaller amounts 0:12:04.240 --> 0:12:06.680 of elements that we don't know about, Right, how much 0:12:07.080 --> 0:12:10.280 of a particular kind of silicon down there is sulfur, 0:12:10.320 --> 0:12:12.400 down there these kinds of questions, and those all just 0:12:12.440 --> 0:12:15.520 help us understand what the building blocks of Earth were 0:12:15.679 --> 0:12:19.959 when Earth formed, and what the geochemistry the kind of 0:12:20.040 --> 0:12:23.720 chemical reactions that can occur as material descends into the Earth. 0:12:23.760 --> 0:12:27.240 That's really where we get that information. But even with diamonds, right, 0:12:27.280 --> 0:12:30.840 we're talking about the outermost layers of the mantle, right, diamonds. 0:12:31.120 --> 0:12:33.319 We don't get diamonds safe from the core mantle boundary 0:12:33.360 --> 0:12:35.280 or anywhere deeper than that. So we can't use the 0:12:35.280 --> 0:12:37.000 diamonds to learn about the deeper parts. 0:12:37.120 --> 0:12:40.079 Is that because diamonds aren't made deeper or because diamonds 0:12:40.120 --> 0:12:41.800 from that far down just don't make it up to 0:12:41.800 --> 0:12:42.280 the surface. 0:12:42.520 --> 0:12:46.000 Mostly the latter, I think also, like if you get 0:12:46.040 --> 0:12:49.520 carbon down there, yeah, it doesn't necessarily join into making 0:12:49.559 --> 0:12:50.560 diamond at that depth. 0:12:50.640 --> 0:12:53.520 All right, So there aren't like huge diamonds buried deep 0:12:53.559 --> 0:12:57.000 in the earth that we are not on Earth, not 0:12:57.120 --> 0:12:59.959 on Earth. Well, that was my whole motivation for digging 0:13:00.040 --> 0:13:02.600 so deeply when I was a kid, fantasizing about revealing 0:13:02.640 --> 0:13:05.600 some you know, boulder sized diamond. All right, So diamonds 0:13:05.600 --> 0:13:07.480 give us one sample of what else can we do? 0:13:07.559 --> 0:13:10.320 What about gravity? What about just studying like the variation 0:13:10.440 --> 0:13:13.440 in Earth's gravity as we you know, orbit to planate 0:13:13.559 --> 0:13:15.319 or look around it. What does that tell us about 0:13:15.320 --> 0:13:16.319 what's inside the Earth. 0:13:16.400 --> 0:13:17.800 The way I like to think about it is, you know, 0:13:17.840 --> 0:13:19.400 if you want to figure out what's going on inside 0:13:19.440 --> 0:13:22.920 the Earth, try and make an analogy to a human body. 0:13:23.000 --> 0:13:24.480 Right if you if you have an ache and you 0:13:24.520 --> 0:13:27.160 go to your doctor and you're like this hurts. Hopefully 0:13:27.160 --> 0:13:29.240 they're not. Their first kind of instinct is not to 0:13:29.320 --> 0:13:30.840 drill a hole in you to figure that out. Right, 0:13:30.880 --> 0:13:33.920 There are ways that they can use different fields and 0:13:33.960 --> 0:13:36.480 different scans to figure out what's wrong with your insides, 0:13:36.520 --> 0:13:38.080 And we can do the same thing for the inside 0:13:38.080 --> 0:13:41.000 of the Earth. So we can scan gravity as you mentioned, 0:13:41.040 --> 0:13:43.280 that's one, Magnetic fields is another one. 0:13:43.440 --> 0:13:45.160 And we can also determine. 0:13:44.800 --> 0:13:47.599 Properties of waves that travel through the Earth from earthquakes 0:13:47.600 --> 0:13:50.280 through seismology. So we can use all these scanning techniques 0:13:50.280 --> 0:13:52.160 to figure out what's going on deeper inside the Earth. 0:13:52.200 --> 0:13:54.120 So what do you mean by using gravity? Is it 0:13:54.200 --> 0:13:56.960 just like measuring the variations of gravity so that we 0:13:57.080 --> 0:13:59.439 understand how the Earth is not a perfect sphere or 0:13:59.640 --> 0:14:02.240 how they'rear is not homogeneous in density. What is it 0:14:02.280 --> 0:14:02.880 we're learning? 0:14:03.000 --> 0:14:03.800 Yeah, great question. 0:14:03.960 --> 0:14:06.440 So, yeah, it really is the fact that both isn't 0:14:06.440 --> 0:14:11.040 a perfect sphere and has some inhomogeneous material below it. Right, 0:14:11.080 --> 0:14:13.040 So if you were walking around with a griviminter that 0:14:13.080 --> 0:14:15.679 could measure gravity and it was really really good and 0:14:15.720 --> 0:14:18.480 you walked around, you would get slightly different values everywhere 0:14:18.480 --> 0:14:20.920 you walk, and that would be determined by the mass 0:14:20.960 --> 0:14:23.960 directly under your feet. And so we can use that information. 0:14:24.120 --> 0:14:27.400 We have spacecraft that orbit the Earth that measure Earth's 0:14:27.400 --> 0:14:30.120 gravity feel to really high precision, and we can use 0:14:30.160 --> 0:14:32.640 that to figure out what is the distribution of density 0:14:32.640 --> 0:14:34.600 inside the Earth. And that kind of allows us to 0:14:34.680 --> 0:14:37.120 kind of image what's going on. Where's the denser stuff 0:14:37.120 --> 0:14:38.720 in the Earth, where's the lighter stuff? And we can 0:14:38.720 --> 0:14:42.240 actually see things like convection cells in the mantle and 0:14:42.480 --> 0:14:45.920 plumes of magma coming up for volcanoes, things like this. 0:14:46.160 --> 0:14:48.640 But gravity is such a weak force. How do you 0:14:49.000 --> 0:14:53.680 identify these variations in density with such an incredibly weak force. 0:14:53.720 --> 0:14:55.360 They must be pretty big effects. 0:14:55.640 --> 0:14:58.120 They aren't. They are very very tiny effect. We're just 0:14:58.240 --> 0:14:59.400 really good at measuring them. 0:15:00.120 --> 0:15:02.720 Emitter, you mentioned this might seem like a weird object 0:15:02.840 --> 0:15:05.120 or listeners. But I guess, like my bathroom scale is 0:15:05.120 --> 0:15:06.800 a gravi emitter. If I walked around the Earth with 0:15:06.840 --> 0:15:10.120 my bathroom scale, I would measure different weights before and 0:15:10.200 --> 0:15:12.920 after lunch, of course, but also if I didn't need anything, 0:15:13.280 --> 0:15:15.880 or I user reference mass, then I guess I would 0:15:15.880 --> 0:15:18.320 measure different accelerations due to gravity. 0:15:18.480 --> 0:15:18.680 Yeah. 0:15:18.680 --> 0:15:20.920 Absolutely, And if you are someone on the surface taking 0:15:20.920 --> 0:15:24.640 gravity measurements, that's exactly the kind of instrument you would use. Interestingly, 0:15:25.120 --> 0:15:28.360 once we get into orbiting around a planet like Earth 0:15:28.560 --> 0:15:31.240 to take measurements, we use a completely different technique. We 0:15:31.360 --> 0:15:34.239 basically use the fact that if we have a spacecraft 0:15:34.240 --> 0:15:36.600 in orbit around the Earth, we know it's in orbit 0:15:36.640 --> 0:15:40.120 around the Earth, and its orbital speed and altitude is 0:15:40.160 --> 0:15:42.600 completely determined by the mass of the planet. 0:15:42.680 --> 0:15:44.080 So we can use things. 0:15:43.880 --> 0:15:47.080 Like two spacecraft just slightly at different locations from each 0:15:47.080 --> 0:15:49.360 other kind of moving around, and we can use the 0:15:49.440 --> 0:15:52.400 distance between the two spacecraft as like a proxy for 0:15:52.480 --> 0:15:54.640 how much g is right where they are, how much 0:15:54.640 --> 0:15:56.360 the gravity is right where they are. So that's actually 0:15:56.360 --> 0:15:58.080 how it's done in practice with spacecraft. 0:15:58.160 --> 0:16:00.640 Wow, that's incredible, And how sensitive are they? I mean, 0:16:00.880 --> 0:16:03.280 like one part in a thousand, one part in a million. 0:16:03.160 --> 0:16:05.200 Yeah, one part in a million. That's where we're getting to. 0:16:05.360 --> 0:16:07.400 Wow, So they can really tell if I've eaten lunch. 0:16:07.600 --> 0:16:09.600 Some spacecraft up there can tell that the mass of 0:16:09.600 --> 0:16:10.640 the Earth has changed. 0:16:11.200 --> 0:16:13.520 One thing they're actually used for. So the Grace satellites, 0:16:13.560 --> 0:16:16.560 which orbited Earth for about ten years, one of their 0:16:16.600 --> 0:16:19.600 main applications was to follow water flow on the surface, 0:16:19.640 --> 0:16:21.840 so you could see, for example, when water was filling 0:16:21.840 --> 0:16:25.560 reservoirs underground reservoirs in certain parts of the country or 0:16:25.560 --> 0:16:27.600 different countries if you wanted to see are we going 0:16:27.640 --> 0:16:30.200 to have a drought, are we in a rainstorm season, 0:16:30.280 --> 0:16:31.880 or what's the water situation going on here? 0:16:31.920 --> 0:16:34.240 So we can even use gravity to tract climate change. 0:16:34.360 --> 0:16:37.240 Wow, that sounds like modern day divining rods. But you're 0:16:37.280 --> 0:16:40.160 actually using science to find the water underground. That's incredible, 0:16:40.200 --> 0:16:42.280 all right, So gravity's one way to do it. You 0:16:42.320 --> 0:16:46.080 also mentioned seismic probes. These are like waves inside the earth. 0:16:46.160 --> 0:16:48.120 How do we use that to see what's going on? 0:16:48.480 --> 0:16:51.760 So every time there's an earthquake, it's like sort of 0:16:52.160 --> 0:16:54.120 something kind of punched the inside of the Earth at 0:16:54.160 --> 0:16:55.920 some point and it causes the Earth to ring. It 0:16:55.960 --> 0:16:59.640 causes waves to travel through the interior of the Earth 0:17:00.120 --> 0:17:02.360 and on the surface of the Earth. If we put 0:17:02.400 --> 0:17:04.359 out a bunch of instruments that can kind of measure 0:17:04.359 --> 0:17:08.119 the shaking, so seismographs, then we can figure out a 0:17:08.119 --> 0:17:08.679 few things. 0:17:08.560 --> 0:17:09.920 About the earthquake waves. 0:17:09.960 --> 0:17:12.600 We can figure out when they arrive at different locations 0:17:12.640 --> 0:17:14.919 around the planet, and how big the waves are, the 0:17:14.920 --> 0:17:16.360 amplitude of the waves. 0:17:16.400 --> 0:17:17.440 And the speed. 0:17:17.480 --> 0:17:20.760 The timing of when the waves arrive is completely directly 0:17:20.800 --> 0:17:24.160 related to the material properties that the waves traveled through. 0:17:24.520 --> 0:17:26.560 So for example, we can figure out the density of 0:17:26.640 --> 0:17:29.959 material that a wave traveled safe from. Let's say an 0:17:29.960 --> 0:17:33.439 earthquake happens in California and the wave travels up to 0:17:34.760 --> 0:17:37.919 Seattle in Washington. You can use that to figure out 0:17:38.000 --> 0:17:40.919 kind of what's the material just under the surface there, 0:17:40.960 --> 0:17:43.320 Whereas if you try to go across the globe to 0:17:43.359 --> 0:17:45.600 another part on the other side, the waves might travel 0:17:45.640 --> 0:17:48.159