1 00:00:00,160 --> 00:00:14,350 [Music] 2 00:00:18,620 --> 00:00:16,790 thanks Kristine I'll say that this is 3 00:00:21,230 --> 00:00:18,630 also my abstract then if you went 4 00:00:24,710 --> 00:00:21,240 looking for one if you actually found a 5 00:00:26,509 --> 00:00:24,720 different title part of it to do with me 6 00:00:28,759 --> 00:00:26,519 deciding what exactly to talk about and 7 00:00:32,030 --> 00:00:28,769 the breadth of this particular 8 00:00:35,510 --> 00:00:32,040 communities was one of the reason gave 9 00:00:37,069 --> 00:00:35,520 me pause as to what I wanted to cover so 10 00:00:38,720 --> 00:00:37,079 what I'm going to talk about is climate 11 00:00:40,270 --> 00:00:38,730 mantle coupling that was what I was 12 00:00:42,500 --> 00:00:40,280 asked to talk about but in particular 13 00:00:44,569 --> 00:00:42,510 the issue is how do you build and 14 00:00:47,660 --> 00:00:44,579 maintain an atmosphere and that really 15 00:00:50,720 --> 00:00:47,670 comes down to how volatile cycling work 16 00:00:53,569 --> 00:00:50,730 and how about a cycling works in terms 17 00:00:56,720 --> 00:00:53,579 of how much atmosphere you produce or 18 00:00:59,540 --> 00:00:56,730 maintain as a lot to do with whether 19 00:01:01,729 --> 00:00:59,550 habitability is even possible and so 20 00:01:02,959 --> 00:01:01,739 volatile cycling talk about there's a 21 00:01:04,820 --> 00:01:02,969 lot to do with whatever the tectonic 22 00:01:06,620 --> 00:01:04,830 regime of births or any other planet 23 00:01:08,960 --> 00:01:06,630 happens to be so how the planets thurs 24 00:01:10,670 --> 00:01:08,970 itself has a lot to do with whatever you 25 00:01:14,179 --> 00:01:10,680 keep an atmosphere whether we can have a 26 00:01:16,130 --> 00:01:14,189 habitable period and how dynamics that 27 00:01:18,469 --> 00:01:16,140 period is the habitability is not a 28 00:01:22,310 --> 00:01:18,479 state property of a planet it's very 29 00:01:24,170 --> 00:01:22,320 much transient in the exoplanet 30 00:01:26,149 --> 00:01:24,180 community this issue of habitable zone 31 00:01:28,880 --> 00:01:26,159 which that's the only time you'll hear 32 00:01:31,069 --> 00:01:28,890 me use that expression it's a big deal 33 00:01:33,410 --> 00:01:31,079 they look for it it's almost like a 34 00:01:35,690 --> 00:01:33,420 hunter looking for a target when I show 35 00:01:37,490 --> 00:01:35,700 you today is that there's any wrong way 36 00:01:41,960 --> 00:01:37,500 to think about that problem that's the 37 00:01:46,280 --> 00:01:41,970 way there is no habitable zone as a very 38 00:01:47,929 --> 00:01:46,290 dynamic property and Adam burrows is a 39 00:01:49,370 --> 00:01:47,939 review series of review papers on the 40 00:01:52,789 --> 00:01:49,380 sort of state of the world an exoplanet 41 00:01:56,780 --> 00:01:52,799 ology a couple of years ago and he kind 42 00:01:59,179 --> 00:01:56,790 of hinted at it in basically pointing 43 00:02:01,550 --> 00:01:59,189 the direction of out of inquiry into 44 00:02:03,109 --> 00:02:01,560 what is the what is the nature of 45 00:02:05,560 --> 00:02:03,119 planetary atmospheres and how do we use 46 00:02:08,600 --> 00:02:05,570 them to understand planetary interiors 47 00:02:10,790 --> 00:02:08,610 went with his paper was going okay so 48 00:02:12,110 --> 00:02:10,800 planets evolved over time then our 49 00:02:13,760 --> 00:02:12,120 atmosphere is evolved over time then 50 00:02:15,710 --> 00:02:13,770 habitability evolves over time 51 00:02:18,200 --> 00:02:15,720 so the idea that son or assistance for 52 00:02:22,430 --> 00:02:18,210 example is the major control is probably 53 00:02:26,450 --> 00:02:22,440 a misleading at the best of times okay 54 00:02:28,010 --> 00:02:26,460 in any event I'm going to be focusing on 55 00:02:31,790 --> 00:02:28,020 terrestrial planets and we have three of 56 00:02:36,380 --> 00:02:31,800 them at least for today Mars Earth and 57 00:02:38,690 --> 00:02:36,390 Venus and volatile cycling comes down to 58 00:02:41,690 --> 00:02:38,700 the sort of three things that enter one 59 00:02:44,780 --> 00:02:41,700 is what's a tectonic regime how does the 60 00:02:46,670 --> 00:02:44,790 tectonic regime and effect or mott or 61 00:02:52,250 --> 00:02:46,680 how is it modified by volcanism and 62 00:02:54,920 --> 00:02:52,260 weathering and then climate so again not 63 00:02:56,270 --> 00:02:54,930 again it gets in more detail break this 64 00:03:00,980 --> 00:02:56,280 out a little bit further there's a lot 65 00:03:05,840 --> 00:03:00,990 involved in each of these three each of 66 00:03:08,510 --> 00:03:05,850 those three I'll learn how to drive this 67 00:03:09,680 --> 00:03:08,520 at some point each of the three monikers 68 00:03:11,270 --> 00:03:09,690 the tectonic regime I'm going to be 69 00:03:13,700 --> 00:03:11,280 focusing on mantle stirring and 70 00:03:15,590 --> 00:03:13,710 structure story mostly stirring so what 71 00:03:18,590 --> 00:03:15,600 is the stirring style how does in 72 00:03:21,170 --> 00:03:18,600 gassing and outgassing work tectonic 73 00:03:24,320 --> 00:03:21,180 regime depends on planets resize a bit 74 00:03:26,000 --> 00:03:24,330 affected by and FX melting and volcanism 75 00:03:29,270 --> 00:03:26,010 where is the mantle melt how is that 76 00:03:31,880 --> 00:03:29,280 melt delivered to the surface stirrings 77 00:03:35,240 --> 00:03:31,890 affected by crust production where does 78 00:03:37,460 --> 00:03:35,250 that happen confident supercontinents it 79 00:03:40,370 --> 00:03:37,470 can add stiff bits to the top of the 80 00:03:41,840 --> 00:03:40,380 mantle which can introduce transients to 81 00:03:44,470 --> 00:03:41,850 the way the planet stores itself and 82 00:03:47,030 --> 00:03:44,480 also affect whether it can stir itself 83 00:03:48,800 --> 00:03:47,040 weathering regime weathering is not just 84 00:03:51,230 --> 00:03:48,810 about temperature it's about how do you 85 00:03:54,470 --> 00:03:51,240 turn rocks into clay in the first part 86 00:03:56,030 --> 00:03:54,480 is a mechanical one and the mechanics of 87 00:03:58,310 --> 00:03:56,040 weathering varies depending whether 88 00:04:00,350 --> 00:03:58,320 we're at subduction zones or it even at 89 00:04:03,800 --> 00:04:00,360 mid-ocean ridges seafloor weathering is 90 00:04:06,740 --> 00:04:03,810 for real but also happens in planets in 91 00:04:08,990 --> 00:04:06,750 continental interiors second part 92 00:04:12,170 --> 00:04:09,000 volcanism introduces greenhouse gases 93 00:04:13,640 --> 00:04:12,180 and aerosols statment sphere it's 94 00:04:15,140 --> 00:04:13,650 radiative properties it's a strong 95 00:04:18,190 --> 00:04:15,150 function of volcanism which is obviously 96 00:04:20,750 --> 00:04:18,200 tied to the way the mental melt 97 00:04:22,640 --> 00:04:20,760 weathering it is affected by volcanism 98 00:04:25,640 --> 00:04:22,650 again by the term by Vulcan is 99 00:04:27,500 --> 00:04:25,650 determining what rocks are around it if 100 00:04:29,720 --> 00:04:27,510 most of the volcanic rocks are basalt 101 00:04:32,000 --> 00:04:29,730 versus a granite then the weathering 102 00:04:34,730 --> 00:04:32,010 potentials become much well much 103 00:04:37,940 --> 00:04:34,740 different volcanism could introduce 104 00:04:40,370 --> 00:04:37,950 phases so aerosols are one kind of 105 00:04:41,600 --> 00:04:40,380 kindred Hayes's or aerosols it can 106 00:04:44,420 --> 00:04:41,610 introduce haze is particularly in a low 107 00:04:47,090 --> 00:04:44,430 oxygen world so volcanic out products 108 00:04:48,620 --> 00:04:47,100 can lead to the formation of black gazes 109 00:04:51,140 --> 00:04:48,630 of white haze is all kinds of things 110 00:04:54,280 --> 00:04:51,150 which affect the climate which in turn 111 00:04:56,900 --> 00:04:54,290 affects the potential / habitability 112 00:05:00,350 --> 00:04:56,910 cross production obvious that enters 113 00:05:02,120 --> 00:05:00,360 into albedo and that has a big effect on 114 00:05:05,230 --> 00:05:02,130 what the average surface temperature on 115 00:05:08,050 --> 00:05:05,240 earth is and how that varies in space 116 00:05:10,040 --> 00:05:08,060 okay it involves like and climate 117 00:05:12,140 --> 00:05:10,050 obviously climate depends on surface 118 00:05:14,090 --> 00:05:12,150 temperature there's all kinds of 119 00:05:15,140 --> 00:05:14,100 feedbacks albedo depends on surface 120 00:05:18,200 --> 00:05:15,150 temperature depends on whether we have 121 00:05:19,520 --> 00:05:18,210 lights so they have rocks weathering 122 00:05:20,420 --> 00:05:19,530 again so whether in gear certainly 123 00:05:24,470 --> 00:05:20,430 depends on temperature precipitation 124 00:05:25,760 --> 00:05:24,480 rates so what you know weathering it's a 125 00:05:27,620 --> 00:05:25,770 a function of precipitation rates 126 00:05:29,390 --> 00:05:27,630 whether you get precipitation depends on 127 00:05:30,710 --> 00:05:29,400 whether you're making mountains and 128 00:05:32,300 --> 00:05:30,720 where those mountains are are they in 129 00:05:35,120 --> 00:05:32,310 the tropics are they in high latitude 130 00:05:37,730 --> 00:05:35,130 and so on it's the point of this anyway 131 00:05:40,670 --> 00:05:37,740 it's indicates that the ball will 132 00:05:44,510 --> 00:05:40,680 slightly mating that governs Earth's 133 00:05:46,460 --> 00:05:44,520 climate or any planet's climate involves 134 00:05:48,140 --> 00:05:46,470 a number of different things that are 135 00:05:49,490 --> 00:05:48,150 very tightly coupled and also complex 136 00:05:53,630 --> 00:05:49,500 there's lots of opportunities for 137 00:05:55,940 --> 00:05:53,640 feedback sand and rich behaviors the 138 00:05:58,610 --> 00:05:55,950 idea of thinking about habitability or 139 00:06:01,700 --> 00:05:58,620 habitable zone I think the idea thinking 140 00:06:04,610 --> 00:06:01,710 about habitable zone is sort of very I 141 00:06:06,710 --> 00:06:04,620 would say to restricted thinking about 142 00:06:07,940 --> 00:06:06,720 all these these three main controls on 143 00:06:10,310 --> 00:06:07,950 and gassing and outgassing and 144 00:06:11,810 --> 00:06:10,320 atmospheric stability the issue is do we 145 00:06:13,280 --> 00:06:11,820 get habitability that's what the 146 00:06:18,350 --> 00:06:13,290 question were interested in how long 147 00:06:20,330 --> 00:06:18,360 does it last and I guess for the purpose 148 00:06:23,960 --> 00:06:20,340 of this symposium to what extent does 149 00:06:26,080 --> 00:06:23,970 that enable habitants as well okay some 150 00:06:28,610 --> 00:06:26,090 issues that enter into the style of 151 00:06:30,500 --> 00:06:28,620 volatile cycling so I'm going to be sort 152 00:06:33,710 --> 00:06:30,510 of focusing mostly on mantle stirring 153 00:06:35,240 --> 00:06:33,720 how that works planetary formation so 154 00:06:37,010 --> 00:06:35,250 how much what is the budget of heat 155 00:06:38,810 --> 00:06:37,020 producing elements in the mantle or 156 00:06:40,400 --> 00:06:38,820 where are the heat producing elements at 157 00:06:40,970 --> 00:06:40,410 the top of the mantle that is bottom the 158 00:06:45,080 --> 00:06:40,980 mantle 159 00:06:47,360 --> 00:06:45,090 stuck in the core planetary age internal 160 00:06:49,580 --> 00:06:47,370 temperature of the mantles we'll talk 161 00:06:51,950 --> 00:06:49,590 about a bit there's a lot to do with the 162 00:06:55,310 --> 00:06:51,960 positive the potential for a given 163 00:06:57,110 --> 00:06:55,320 tectonic regime and age has a lot to do 164 00:06:59,570 --> 00:06:57,120 is well the strength of radiogenic 165 00:07:02,270 --> 00:06:59,580 heating so young planets of different 166 00:07:04,520 --> 00:07:02,280 heating rates than old planets a big one 167 00:07:08,630 --> 00:07:04,530 history what is the history of tectonic 168 00:07:10,310 --> 00:07:08,640 deformation tectonic motion it turns out 169 00:07:12,500 --> 00:07:10,320 that the evolutionary path the planet 170 00:07:15,020 --> 00:07:12,510 takes depends on where it's been it like 171 00:07:16,250 --> 00:07:15,030 humans that gets in that way that's 172 00:07:19,900 --> 00:07:16,260 depending on how we spend our teenage 173 00:07:24,110 --> 00:07:19,910 years we end up as a professor or not 174 00:07:26,590 --> 00:07:24,120 and on my teenage years I can say nobody 175 00:07:28,580 --> 00:07:26,600 would have guessed I'd be a professor 176 00:07:30,170 --> 00:07:28,590 most of what I'm going to show you the 177 00:07:32,090 --> 00:07:30,180 tectonic particularly with the tectonic 178 00:07:33,830 --> 00:07:32,100 regimes you get plate tectonics not 179 00:07:37,000 --> 00:07:33,840 plate tectonics something in between all 180 00:07:41,390 --> 00:07:37,010 those solutions are usually permitted 181 00:07:43,700 --> 00:07:41,400 say that again Mars Venus are solutions 182 00:07:45,380 --> 00:07:43,710 for an evolutionary paths are almost 183 00:07:47,300 --> 00:07:45,390 equally plausible the beginning of 184 00:07:50,920 --> 00:07:47,310 Earth's time that an earth end up the 185 00:07:53,660 --> 00:07:50,930 way it is is not a foregone conclusion 186 00:07:55,040 --> 00:07:53,670 tectonic resilience so earth ended up in 187 00:07:57,500 --> 00:07:55,050 a plate tectonic regime and managed to 188 00:08:00,380 --> 00:07:57,510 stay there that is a kind of amazing 189 00:08:04,130 --> 00:08:00,390 thing so what controls the resilience of 190 00:08:06,230 --> 00:08:04,140 that particular attractor okay if you 191 00:08:07,880 --> 00:08:06,240 broad questions so you can read faster 192 00:08:11,480 --> 00:08:07,890 that I'm good you can read faster that 193 00:08:13,910 --> 00:08:11,490 I'm going to say but yeah but you're 194 00:08:16,940 --> 00:08:13,920 beyond my talk is sort of partly for 195 00:08:18,590 --> 00:08:16,950 discussion so is the habitability that 196 00:08:22,670 --> 00:08:18,600 has left it so long a natural 197 00:08:27,050 --> 00:08:22,680 consequence of Earth's or current 198 00:08:29,660 --> 00:08:27,060 tectonic regime is our current earth 199 00:08:33,260 --> 00:08:29,670 some product or somehow related to an 200 00:08:34,940 --> 00:08:33,270 early crisis impact history or impact 201 00:08:36,980 --> 00:08:34,950 erosion a pledge which will do a thought 202 00:08:38,900 --> 00:08:36,990 experiment related to that so do the 203 00:08:40,219 --> 00:08:38,910 very initial conditions enter into where 204 00:08:44,030 --> 00:08:40,229 we are now and how does that how does 205 00:08:46,520 --> 00:08:44,040 that work is our current tectonic regime 206 00:08:48,800 --> 00:08:46,530 and climatic resilience product of the 207 00:08:50,990 --> 00:08:48,810 way we started in how we evolved along 208 00:08:52,910 --> 00:08:51,000 that path so is the memory of the 209 00:08:55,240 --> 00:08:52,920 beginning of plate tectonics for example 210 00:08:57,829 --> 00:08:55,250 or the way in which the first 211 00:09:01,639 --> 00:08:57,839 solidified the rheological structure 212 00:09:03,650 --> 00:09:01,649 that emerged from that has that played a 213 00:09:06,769 --> 00:09:03,660 big part in letting leading earth to 214 00:09:10,610 --> 00:09:06,779 where it is and as finally that what are 215 00:09:12,110 --> 00:09:10,620 the big links between the mantle dynamic 216 00:09:15,680 --> 00:09:12,120 controls on the probability for 217 00:09:17,990 --> 00:09:15,690 habitability inhabitants inhabitants 218 00:09:19,610 --> 00:09:18,000 themselves and I'll show you an example 219 00:09:21,620 --> 00:09:19,620 of the time to do the thought experiment 220 00:09:24,110 --> 00:09:21,630 I want to do but one question is to what 221 00:09:28,190 --> 00:09:24,120 extent is long period tectonically 222 00:09:30,110 --> 00:09:28,200 driven changes in climate impose 223 00:09:33,139 --> 00:09:30,120 environmental stresses that are 224 00:09:35,720 --> 00:09:33,149 expressed in the biological record and 225 00:09:39,199 --> 00:09:35,730 we'll look at one example in a moment 226 00:09:42,319 --> 00:09:39,209 but what to do today is talk a bit about 227 00:09:43,759 --> 00:09:42,329 how you write this problem down so what 228 00:09:45,920 --> 00:09:43,769 are the some of the underlying mechanics 229 00:09:47,569 --> 00:09:45,930 that go into thinking about the tectonic 230 00:09:49,819 --> 00:09:47,579 regime of a planet the weights thurs 231 00:09:52,850 --> 00:09:49,829 itself the major control and in gassing 232 00:09:54,259 --> 00:09:52,860 and outgassing and then we're going to 233 00:10:00,100 --> 00:09:54,269 do three thought experiments I hope to 234 00:10:02,960 --> 00:10:00,110 get through to the first is a simple one 235 00:10:05,600 --> 00:10:02,970 if we beat up we throw rocks at Earth 236 00:10:08,060 --> 00:10:05,610 early right after the magma ocean 237 00:10:09,829 --> 00:10:08,070 finished solidifying assuming is a bit 238 00:10:11,870 --> 00:10:09,839 of crust on top you lose that crust of 239 00:10:13,759 --> 00:10:11,880 space you lose some heat production does 240 00:10:15,230 --> 00:10:13,769 that put earth on an evolutionary path 241 00:10:17,630 --> 00:10:15,240 that is more likely to end up and the 242 00:10:20,930 --> 00:10:17,640 regime we're in now as opposed to say 243 00:10:23,480 --> 00:10:20,940 Venus what we're not going to talk about 244 00:10:24,680 --> 00:10:23,490 but it's interesting to think about if 245 00:10:27,319 --> 00:10:24,690 anyone's interested in talking about a 246 00:10:29,329 --> 00:10:27,329 can offline but this is a huge one so 247 00:10:31,220 --> 00:10:29,339 intermittent transient super continental 248 00:10:32,509 --> 00:10:31,230 cycles lock up the earth we're going to 249 00:10:33,920 --> 00:10:32,519 shipping to show you a simulation of one 250 00:10:37,610 --> 00:10:33,930 in just a minute they lock up the way 251 00:10:39,439 --> 00:10:37,620 there are stirs itself and the question 252 00:10:41,420 --> 00:10:39,449 is can they drive climatic crises like 253 00:10:44,600 --> 00:10:41,430 snowball earth and the answer is yes 254 00:10:48,019 --> 00:10:44,610 they can at least we have models that do 255 00:10:49,910 --> 00:10:48,029 that and at least in the cryogenic the 256 00:10:51,740 --> 00:10:49,920 last snowball earth produced a 257 00:10:54,139 --> 00:10:51,750 biological opportunity to show you in 258 00:10:57,050 --> 00:10:54,149 just a moment you want to hope we do do 259 00:10:59,150 --> 00:10:57,060 I hope I do get to is the more 260 00:11:00,500 --> 00:10:59,160 interesting one I think for sort of the 261 00:11:03,470 --> 00:11:00,510 general picture for how its retro 262 00:11:07,699 --> 00:11:03,480 planets work which is how resilient is 263 00:11:08,690 --> 00:11:07,709 the climate climate of earth to time 264 00:11:10,640 --> 00:11:08,700 dependence and 265 00:11:13,670 --> 00:11:10,650 tecktonik regime that is evident in 266 00:11:14,900 --> 00:11:13,680 proxy data I'm going to show you all 267 00:11:16,490 --> 00:11:14,910 right the first thing I'm not going to 268 00:11:18,920 --> 00:11:16,500 talk about just because it's interesting 269 00:11:22,220 --> 00:11:18,930 to think about so time on the x-axis 270 00:11:26,030 --> 00:11:22,230 here so this is 1.6 billion years ago 271 00:11:27,530 --> 00:11:26,040 this is now and what you're looking at 272 00:11:29,870 --> 00:11:27,540 the blue bar if you can't read it this 273 00:11:31,070 --> 00:11:29,880 is snowball earth this is about 740 274 00:11:34,310 --> 00:11:31,080 million years that's six hundred and 275 00:11:35,210 --> 00:11:34,320 five million years at the other end and 276 00:11:37,250 --> 00:11:35,220 what you're looking at a few different 277 00:11:40,460 --> 00:11:37,260 lines the Blue is the rise of oxygen 278 00:11:42,620 --> 00:11:40,470 Green is total biomass so billion years 279 00:11:44,060 --> 00:11:42,630 up until the end of the cryogen you in 280 00:11:47,120 --> 00:11:44,070 the world was dominated by single-cell 281 00:11:49,850 --> 00:11:47,130 dudes they had a good time right they 282 00:11:51,320 --> 00:11:49,860 ran the show four billion years the end 283 00:11:54,580 --> 00:11:51,330 of the melt out which by the way 284 00:11:56,930 --> 00:11:54,590 happened during the break up of Rodinia 285 00:11:59,060 --> 00:11:56,940 five million years is about how long it 286 00:12:01,850 --> 00:11:59,070 took for the essential diversity we see 287 00:12:04,060 --> 00:12:01,860 now to begin to emerge five million 288 00:12:06,770 --> 00:12:04,070 years after billion years of stability 289 00:12:09,050 --> 00:12:06,780 the question that we don't have time to 290 00:12:12,080 --> 00:12:09,060 talk about is to what extent did the 291 00:12:14,480 --> 00:12:12,090 formation and breakup of rodinia affect 292 00:12:17,540 --> 00:12:14,490 climate and effect structure of the 293 00:12:18,830 --> 00:12:17,550 oceans possibly to give rise to the 294 00:12:21,230 --> 00:12:18,840 environmental stresses that may have 295 00:12:22,790 --> 00:12:21,240 given rise to this change whether it's 296 00:12:24,170 --> 00:12:22,800 an instability or an expression of by 297 00:12:29,630 --> 00:12:24,180 stability I don't know but it's 298 00:12:31,880 --> 00:12:29,640 interesting okay do you plate tectonics 299 00:12:32,900 --> 00:12:31,890 to earth smoothly continuously okay 300 00:12:35,090 --> 00:12:32,910 raise your hand if you think you think 301 00:12:38,060 --> 00:12:35,100 they do say select onyx is always taught 302 00:12:41,600 --> 00:12:38,070 as being a slow gradual thing so who the 303 00:12:46,460 --> 00:12:41,610 students in here raise your hand all 304 00:12:50,270 --> 00:12:46,470 just one student in here okay who's not 305 00:12:53,000 --> 00:12:50,280 a student in here all right everyone 306 00:12:54,350 --> 00:12:53,010 who's not raising their hand so how does 307 00:12:56,210 --> 00:12:54,360 this place iconic stir the earth 308 00:13:01,760 --> 00:12:56,220 smoothly I just I got a laser pointer 309 00:13:08,300 --> 00:13:01,770 pointing right at you know I was behind 310 00:13:10,040 --> 00:13:08,310 you that's it you you are now but ok but 311 00:13:15,320 --> 00:13:10,050 displace tectonic stir it stir it stir 312 00:13:16,850 --> 00:13:15,330 the earth smoothly and continuously he's 313 00:13:18,480 --> 00:13:16,860 the professor right now I don't want to 314 00:13:20,590 --> 00:13:18,490 answer the question 315 00:13:23,710 --> 00:13:20,600 alright you got to move on otherwise 316 00:13:26,350 --> 00:13:23,720 Christine will get to me so the answer 317 00:13:29,950 --> 00:13:26,360 is it's interesting right that's another 318 00:13:31,630 --> 00:13:29,960 professor Li answer four billion years 319 00:13:34,150 --> 00:13:31,640 ago now these are a bunch of different 320 00:13:36,220 --> 00:13:34,160 proxies for internal and external 321 00:13:39,670 --> 00:13:36,230 dynamic or integral solid body dynamics 322 00:13:42,760 --> 00:13:39,680 to the way the earthworks going to kill 323 00:13:44,920 --> 00:13:42,770 it no maybe the first plot plate 324 00:13:46,870 --> 00:13:44,930 velocities this is apparent plate 325 00:13:49,990 --> 00:13:46,880 velocity so using paleo magnetic data 326 00:13:52,570 --> 00:13:50,000 and ages to get it relative motions 327 00:13:53,890 --> 00:13:52,580 between plates and what you see is to go 328 00:13:55,690 --> 00:13:53,900 back through time and there are peaks 329 00:13:58,180 --> 00:13:55,700 there were plate where relative motions 330 00:14:00,010 --> 00:13:58,190 are fast and slow paleo magnetic 331 00:14:01,780 --> 00:14:00,020 intensity John's probably talked to a 332 00:14:04,360 --> 00:14:01,790 number of you guys about this the dipole 333 00:14:06,780 --> 00:14:04,370 moment is varied a lot in time and it 334 00:14:09,430 --> 00:14:06,790 has almost killed the laser pointer 335 00:14:11,350 --> 00:14:09,440 high-low high-low those that those 336 00:14:16,150 --> 00:14:11,360 variations are getting more robust to 337 00:14:17,620 --> 00:14:16,160 not less as time goes on passive margin 338 00:14:22,930 --> 00:14:17,630 longevity who knows what a passive 339 00:14:28,210 --> 00:14:22,940 margin is two people three people ok 340 00:14:30,370 --> 00:14:28,220 what's the fasted margin John okay it's 341 00:14:33,340 --> 00:14:30,380 boring nothing much nothing much happens 342 00:14:38,470 --> 00:14:33,350 okay we're passive margin longevity is 343 00:14:43,360 --> 00:14:38,480 long often metamorphic gradients well 344 00:14:45,910 --> 00:14:43,370 when passive margin sorry is long often 345 00:14:49,540 --> 00:14:45,920 metamorphic gradients are well Louis 346 00:14:50,830 --> 00:14:49,550 compared to the peak because the data is 347 00:14:54,520 --> 00:14:50,840 sort of interesting so where you have 348 00:14:55,840 --> 00:14:54,530 nothing happening you don't have a lot 349 00:14:57,220 --> 00:14:55,850 basically that the gradients through 350 00:14:58,990 --> 00:14:57,230 confidence are very low we have a lot 351 00:15:01,390 --> 00:14:59,000 happening types of marginal entities 352 00:15:03,760 --> 00:15:01,400 it's very low we have steep metamorphic 353 00:15:06,040 --> 00:15:03,770 gradients so in this particular case 354 00:15:08,230 --> 00:15:06,050 there's lots of heat transfer confidence 355 00:15:09,700 --> 00:15:08,240 are getting beat up form destructed lots 356 00:15:11,860 --> 00:15:09,710 of heat transfer through the continents 357 00:15:15,220 --> 00:15:11,870 for no passive margin they're getting 358 00:15:18,100 --> 00:15:15,230 eaten up all right so the evolution of 359 00:15:19,840 --> 00:15:18,110 Earth's confidence or because it gives 360 00:15:24,370 --> 00:15:19,850 us Wilson cycles with it they don't 361 00:15:26,140 --> 00:15:24,380 exist yet is increases and decreases in 362 00:15:27,940 --> 00:15:26,150 passive margin lunge Avenue take telling 363 00:15:31,020 --> 00:15:27,950 us about periods where the earth is very 364 00:15:32,350 --> 00:15:31,030 very active tectonic Lee and we're isn't 365 00:15:34,090 --> 00:15:32,360 commodious 366 00:15:36,280 --> 00:15:34,100 leave alone magnesium so people talk 367 00:15:37,810 --> 00:15:36,290 about the Earth's mantle getting warmer 368 00:15:39,310 --> 00:15:37,820 back through time and magnesium being a 369 00:15:42,400 --> 00:15:39,320 proxy well yeah it's high back through 370 00:15:44,620 --> 00:15:42,410 that but it oscillates if you look down 371 00:15:47,259 --> 00:15:44,630 at what's called Ozzie and depletion 372 00:15:50,470 --> 00:15:47,269 ages which rotana qualifies it's a way 373 00:15:52,420 --> 00:15:50,480 of dating when you build crayons the 374 00:15:55,329 --> 00:15:52,430 production of crayons the oldest part of 375 00:15:57,160 --> 00:15:55,339 continents again it happens in Peaks 376 00:16:01,030 --> 00:15:57,170 whole bunch is built three billion years 377 00:16:06,850 --> 00:16:01,040 ago then two etc so the picture here is 378 00:16:11,759 --> 00:16:06,860 time dependent thank you the time 379 00:16:17,800 --> 00:16:15,970 so this is another data another example 380 00:16:19,449 --> 00:16:17,810 of that time dependent so this is this 381 00:16:22,420 --> 00:16:19,459 is now now that's three and a half 382 00:16:25,840 --> 00:16:22,430 billion years ago the colored bar is are 383 00:16:28,259 --> 00:16:25,850 the ages of gold deposits who thinks 384 00:16:30,699 --> 00:16:28,269 about gold deposits in this room anybody 385 00:16:33,280 --> 00:16:30,709 one person all right mark karishma 386 00:16:35,230 --> 00:16:33,290 thinks about gold deposits to see you go 387 00:16:37,870 --> 00:16:35,240 back through time is the production of 388 00:16:41,439 --> 00:16:37,880 gold is periodic or not periodic but 389 00:16:43,150 --> 00:16:41,449 intermittent superposed on to that this 390 00:16:46,900 --> 00:16:43,160 line in the background or zircon ages 391 00:16:49,090 --> 00:16:46,910 these are these are mother through cons 392 00:16:51,610 --> 00:16:49,100 form at about 800 degrees in Granite's 393 00:16:54,639 --> 00:16:51,620 so they're tracking they are related to 394 00:16:56,230 --> 00:16:54,649 the production of granite which are how 395 00:16:58,240 --> 00:16:56,240 confident switcher parts of confidences 396 00:17:01,389 --> 00:16:58,250 they form so the related to core 397 00:17:03,850 --> 00:17:01,399 complexes and so on so we're looking at 398 00:17:06,460 --> 00:17:03,860 is the production of crust happening 399 00:17:08,199 --> 00:17:06,470 also in time dependent ways gold 400 00:17:11,010 --> 00:17:08,209 deposits Utah independent crust happens 401 00:17:14,280 --> 00:17:11,020 time-dependent waves what about climate 402 00:17:16,720 --> 00:17:14,290 subject to what I'm talking about today 403 00:17:18,159 --> 00:17:16,730 so one of the biggest mysteries is you 404 00:17:20,350 --> 00:17:18,169 go back through time as you know the 405 00:17:22,299 --> 00:17:20,360 cryogenic and snowball earth is here 600 406 00:17:25,650 --> 00:17:22,309 million years ago to 742 they're about 407 00:17:27,880 --> 00:17:25,660 the one background 2.3 is hotly debated 408 00:17:31,360 --> 00:17:27,890 one of the big mysteries is why the 409 00:17:34,530 --> 00:17:31,370 earth did not have profound glaciation 410 00:17:37,539 --> 00:17:34,540 early on when the Sun is weak alright so 411 00:17:39,310 --> 00:17:37,549 episodic tectonics is somehow modulated 412 00:17:41,560 --> 00:17:39,320 Earth's climate to produce glaciation 413 00:17:44,730 --> 00:17:41,570 only relatively recently episodic 414 00:17:46,560 --> 00:17:44,740 behavior anyway early 415 00:17:49,470 --> 00:17:46,570 all right is the time dependence of 416 00:17:53,130 --> 00:17:49,480 surprise now again the beginning said 417 00:17:55,290 --> 00:17:53,140 okay the way volatile cycling works the 418 00:17:58,350 --> 00:17:55,300 major control is how does the mantle 419 00:18:01,350 --> 00:17:58,360 stir it gases into itself and leave and 420 00:18:04,590 --> 00:18:01,360 relieve them so to make this point we're 421 00:18:06,710 --> 00:18:04,600 going to watch a movie and this is a 422 00:18:09,120 --> 00:18:06,720 numerical analyst view of the current 423 00:18:12,290 --> 00:18:09,130 continental distribution so I guess this 424 00:18:14,880 --> 00:18:12,300 is for Tobias well basically Africa 425 00:18:16,440 --> 00:18:14,890 highly pixelated so the first three 426 00:18:17,760 --> 00:18:16,450 movies are different ways of looking at 427 00:18:19,500 --> 00:18:17,770 continents who's the pit plate 428 00:18:22,790 --> 00:18:19,510 boundaries horizontal velocities and 429 00:18:24,840 --> 00:18:22,800 strain rates bottom is heat transfer 430 00:18:27,660 --> 00:18:24,850 temperature this is plates going down 431 00:18:29,490 --> 00:18:27,670 and plumes rising so each of these 432 00:18:32,280 --> 00:18:29,500 simulations the middle is the core it's 433 00:18:35,430 --> 00:18:32,290 hot the top is cold there's a mustiness 434 00:18:37,680 --> 00:18:35,440 fear and the plates are strong just want 435 00:18:41,460 --> 00:18:37,690 you to watch the movie thinking about 436 00:18:43,380 --> 00:18:41,470 the fact that it's all outgassing 437 00:18:46,260 --> 00:18:43,390 atmospheric production is all about 438 00:18:47,910 --> 00:18:46,270 stirring if you look at the interior 439 00:18:50,610 --> 00:18:47,920 mantle everywhere you see an upwelling 440 00:18:52,799 --> 00:18:50,620 that is where volcanism is happening 441 00:18:54,510 --> 00:18:52,809 crustal production you can see in the 442 00:18:55,350 --> 00:18:54,520 confidence and in the response of the 443 00:18:58,169 --> 00:18:55,360 plates there's an inherent 444 00:19:00,510 --> 00:18:58,179 time-dependent what we're looking at now 445 00:19:03,360 --> 00:19:00,520 is confident slowly forming up to form a 446 00:19:04,710 --> 00:19:03,370 supercontinent if they bounced around 447 00:19:06,450 --> 00:19:04,720 they wandered around until they locked 448 00:19:09,090 --> 00:19:06,460 up and they get stuck here now this is a 449 00:19:11,610 --> 00:19:09,100 billion years of Earth history in a few 450 00:19:14,010 --> 00:19:11,620 seconds but the key thing here is that 451 00:19:15,930 --> 00:19:14,020 in this particular simulation which is 452 00:19:18,570 --> 00:19:15,940 relatively high end in terms of what's 453 00:19:20,370 --> 00:19:18,580 in it including plates a fairly complex 454 00:19:21,870 --> 00:19:20,380 rheology and just letting the earth do 455 00:19:29,220 --> 00:19:21,880 what it does is it in here in time 456 00:19:33,590 --> 00:19:29,230 dependence okay now so basic mechanics 457 00:19:37,320 --> 00:19:33,600 so mantle stirring a volatile exchange 458 00:19:39,780 --> 00:19:37,330 comes down to breaking plates and moving 459 00:19:45,270 --> 00:19:39,790 them around start with so look at two 460 00:19:47,580 --> 00:19:45,280 concepts first is to break a plate if 461 00:19:49,290 --> 00:19:47,590 you imagine growing a math growing a 462 00:19:51,049 --> 00:19:49,300 mantle at the end of the magma ocean 463 00:19:53,760 --> 00:19:51,059 period and having a little sphere on top 464 00:19:56,159 --> 00:19:53,770 and forming a drip beneath it to break a 465 00:19:58,050 --> 00:19:56,169 plate flow into the drip forming beneath 466 00:20:00,690 --> 00:19:58,060 a plate 467 00:20:03,090 --> 00:20:00,700 are lit this year has to pull down on 468 00:20:05,100 --> 00:20:03,100 that plate enough or strongly enough to 469 00:20:08,340 --> 00:20:05,110 actually break it so what matters is how 470 00:20:10,880 --> 00:20:08,350 fast the drip is going and how viscous 471 00:20:13,740 --> 00:20:10,890 it is so this particular case the drip 472 00:20:16,620 --> 00:20:13,750 has a newtonian rheology looks like this 473 00:20:17,970 --> 00:20:16,630 and have to outdo you a yield stress the 474 00:20:20,280 --> 00:20:17,980 yield stress depends on a number of 475 00:20:22,170 --> 00:20:20,290 things depends on how many balls with 476 00:20:24,360 --> 00:20:22,180 the volatile budget is what and what the 477 00:20:27,570 --> 00:20:24,370 lithosphere is actually made of and then 478 00:20:28,770 --> 00:20:27,580 the speed of the drip also matters so 479 00:20:31,680 --> 00:20:28,780 this particular picture which is 480 00:20:33,510 --> 00:20:31,690 relatively naive if the drip falls down 481 00:20:35,280 --> 00:20:33,520 it can break a plate well let me get 482 00:20:39,210 --> 00:20:35,290 plate tectonics to start and we can go 483 00:20:41,040 --> 00:20:39,220 from one plate to more than one well the 484 00:20:46,320 --> 00:20:41,050 key issue is how big is this viscous 485 00:20:48,510 --> 00:20:46,330 stress sorry more interesting and deeper 486 00:20:49,950 --> 00:20:48,520 picture is to realize that as you pull 487 00:20:52,350 --> 00:20:49,960 down on the plate we do some deformation 488 00:20:54,240 --> 00:20:52,360 at the top so as soon as we have 489 00:20:56,130 --> 00:20:54,250 deformation to top there's topography 490 00:20:58,740 --> 00:20:56,140 here that this area's higher than this 491 00:21:01,430 --> 00:20:58,750 and so there are lateral differences in 492 00:21:03,750 --> 00:21:01,440 hydrostatic pressures this topography is 493 00:21:06,780 --> 00:21:03,760 enabling lithosphere that's over here to 494 00:21:08,430 --> 00:21:06,790 try and slow in to fill the gap so 495 00:21:09,900 --> 00:21:08,440 there's one restoring force interest of 496 00:21:12,810 --> 00:21:09,910 problems we pull down on this at some 497 00:21:14,640 --> 00:21:12,820 rate there's a rate at which flows 498 00:21:18,000 --> 00:21:14,650 little sphere into that gap is trying to 499 00:21:19,500 --> 00:21:18,010 anneal the boundary these dash lines are 500 00:21:22,140 --> 00:21:19,510 an attempt to show you the other part 501 00:21:23,910 --> 00:21:22,150 which is micro structural damage as the 502 00:21:26,310 --> 00:21:23,920 plate pulls down a little sphere and 503 00:21:28,740 --> 00:21:26,320 changes the fabric there's memory of 504 00:21:31,860 --> 00:21:28,750 that fabric so the two other issues that 505 00:21:34,110 --> 00:21:31,870 enter is well are we pulling down on 506 00:21:36,330 --> 00:21:34,120 this fast enough to keep this plate 507 00:21:37,920 --> 00:21:36,340 boundary open before it heals itself and 508 00:21:39,480 --> 00:21:37,930 that could dependent the healing rake 509 00:21:42,900 --> 00:21:39,490 it's been a temperature composition 510 00:21:45,780 --> 00:21:42,910 volatiles in history and what is the 511 00:21:48,180 --> 00:21:45,790 memory of this damage so we're 512 00:21:49,920 --> 00:21:48,190 introducing damage and how does that 513 00:21:53,670 --> 00:21:49,930 affect the way that the mantle moves are 514 00:21:56,730 --> 00:21:53,680 the mantle about beyond that okay so 515 00:21:59,220 --> 00:21:56,740 very quickly overview of some of the 516 00:22:00,750 --> 00:21:59,230 basics so stagnant lid one plate planets 517 00:22:02,460 --> 00:22:00,760 happen where the pull down stress the 518 00:22:05,010 --> 00:22:02,470 convective stress is less than those a 519 00:22:07,440 --> 00:22:05,020 spheric yield stress basically drips 520 00:22:09,630 --> 00:22:07,450 can't pull down and break it the 521 00:22:11,270 --> 00:22:09,640 convective stress declines with 522 00:22:12,560 --> 00:22:11,280 increasing mantle temperatures the more 523 00:22:15,650 --> 00:22:12,570 heat production for example we have in 524 00:22:17,120 --> 00:22:15,660 here the less this is if the stress that 525 00:22:19,220 --> 00:22:17,130 we're pulling down with it equals the 526 00:22:21,770 --> 00:22:19,230 yield stress well then we're and we can 527 00:22:24,860 --> 00:22:21,780 go either way so this is a sort of basic 528 00:22:26,420 --> 00:22:24,870 condition for an episodic regime if the 529 00:22:27,980 --> 00:22:26,430 convective stress is bigger than a yield 530 00:22:29,600 --> 00:22:27,990 stress and we can maintain it that way 531 00:22:33,050 --> 00:22:29,610 then in principle we can have a plate 532 00:22:34,430 --> 00:22:33,060 tectonic regime convective stresses are 533 00:22:39,050 --> 00:22:34,440 very sensitive temperatures I've 534 00:22:42,500 --> 00:22:39,060 mentioned and yield stresses are very 535 00:22:48,980 --> 00:22:42,510 sensitive to the volatile budget okay 536 00:22:52,040 --> 00:22:48,990 now more modern view the problem with 537 00:22:54,020 --> 00:22:52,050 earth is that a direction matters in 538 00:22:56,090 --> 00:22:54,030 terms of how we do those experiments of 539 00:23:00,230 --> 00:22:56,100 breaking and getting plates to grow and 540 00:23:01,910 --> 00:23:00,240 break this is a sort of beautiful the 541 00:23:05,480 --> 00:23:01,920 end of a beautiful PhD by Matt Weller 542 00:23:07,340 --> 00:23:05,490 and what this is is it not it's non 543 00:23:09,380 --> 00:23:07,350 dimensional internal heating rate on the 544 00:23:10,700 --> 00:23:09,390 y-axis and a yield stress on the left so 545 00:23:13,700 --> 00:23:10,710 this is the strength of plates and if I 546 00:23:16,220 --> 00:23:13,710 choose one and we do an experiment where 547 00:23:18,800 --> 00:23:16,230 I ask the question if I begin in a 548 00:23:25,130 --> 00:23:18,810 stagette lid regime in this case and I 549 00:23:28,390 --> 00:23:25,140 increase it the internal heating rate or 550 00:23:31,040 --> 00:23:28,400 I move up in internal heating rates paid 551 00:23:35,960 --> 00:23:31,050 the transition to stagette lid if I 552 00:23:39,350 --> 00:23:35,970 begin here and go up happens down here 553 00:23:40,970 --> 00:23:39,360 if I begin the same experiment at high 554 00:23:46,120 --> 00:23:40,980 heating rates and decrease the heating 555 00:23:50,690 --> 00:23:48,500 the regime diagram here is we've got 556 00:23:53,480 --> 00:23:50,700 several different modes stag and lead 557 00:23:56,950 --> 00:23:53,490 one plate plate tectonics multimode is 558 00:23:59,660 --> 00:23:56,960 both plates and not plates are possible 559 00:24:03,230 --> 00:23:59,670 if I choose the lithospheric yield 560 00:24:07,280 --> 00:24:03,240 stress and I increase I move up the 561 00:24:08,780 --> 00:24:07,290 internal heating rate the transition or 562 00:24:10,670 --> 00:24:08,790 the earth or where the transition from 563 00:24:12,440 --> 00:24:10,680 stagette lid to multiple multimode 564 00:24:13,880 --> 00:24:12,450 behavior happens happens at a different 565 00:24:16,040 --> 00:24:13,890 location internal heating rate space 566 00:24:18,950 --> 00:24:16,050 then if I run the experiment the other 567 00:24:21,860 --> 00:24:18,960 way so there's a directionality to this 568 00:24:26,500 --> 00:24:21,870 a bit of hysteresis to look at it 569 00:24:31,580 --> 00:24:29,540 and I in terms of a bi of stability 570 00:24:33,950 --> 00:24:31,590 diagram so up here we've got a number of 571 00:24:35,420 --> 00:24:33,960 things going on so one is the condition 572 00:24:37,460 --> 00:24:35,430 that we're going to play with the 573 00:24:40,460 --> 00:24:37,470 tectonic States a stagette lid and plate 574 00:24:42,740 --> 00:24:40,470 tectonics and a convective vigor so but 575 00:24:44,780 --> 00:24:42,750 again with no plate tectonics and I go 576 00:24:50,780 --> 00:24:44,790 this way I can be in either plate 577 00:24:56,510 --> 00:24:50,790 tectonic or a stagnant lid regime what 578 00:24:57,800 --> 00:24:56,520 the simulations jet what's the point 579 00:25:00,470 --> 00:24:57,810 what the plot shows we don't project 580 00:25:03,470 --> 00:25:00,480 this back down onto a surface at the 581 00:25:08,540 --> 00:25:03,480 bottom is if I begin in a stagnant lid 582 00:25:12,910 --> 00:25:08,550 regime and I change the experimental 583 00:25:14,960 --> 00:25:12,920 condition let's say increase well we do 584 00:25:28,760 --> 00:25:14,970 going to change things let's just look 585 00:25:32,420 --> 00:25:28,770 at surface temperature okay so great all 586 00:25:34,430 --> 00:25:32,430 right let me yeah okay so one of the 587 00:25:37,700 --> 00:25:34,440 ways we can turn plate tectonics off is 588 00:25:40,640 --> 00:25:37,710 by making the surface need to come back 589 00:25:42,320 --> 00:25:40,650 to this cartoon one of the ways we can 590 00:25:45,370 --> 00:25:42,330 close up plate boundaries is by making 591 00:25:47,750 --> 00:25:45,380 the surface warm so if I turn if I 592 00:25:50,570 --> 00:25:47,760 increase the surface temperature the 593 00:25:53,090 --> 00:25:50,580 planet to greenhouse forces we increase 594 00:25:56,330 --> 00:25:53,100 the client we change the temperature of 595 00:25:58,640 --> 00:25:56,340 Earth's surface by say 10 or 50 or 596 00:25:59,990 --> 00:25:58,650 hundred degrees by greenhouse forcing we 597 00:26:01,610 --> 00:26:00,000 make the top of the little sphere more 598 00:26:05,510 --> 00:26:01,620 runny and we have a better chance of 599 00:26:06,830 --> 00:26:05,520 annealing that particular boundary if we 600 00:26:09,380 --> 00:26:06,840 go it look they're looking at this 601 00:26:13,130 --> 00:26:09,390 particular situation if we begin in a 602 00:26:17,270 --> 00:26:13,140 stagette lid regime which is this red 603 00:26:18,560 --> 00:26:17,280 dot and I go I decrease the surface 604 00:26:20,240 --> 00:26:18,570 temperatures so in principle I'm 605 00:26:22,130 --> 00:26:20,250 increasing the ability to keep a plate 606 00:26:25,700 --> 00:26:22,140 boundary open but you can see is we 607 00:26:27,890 --> 00:26:25,710 never actually get out if I begin in a 608 00:26:30,800 --> 00:26:27,900 plate tectonic regime and I increase the 609 00:26:33,500 --> 00:26:30,810 surface temperature we get it an easy 610 00:26:35,600 --> 00:26:33,510 way we get a transition to stagnant lit 611 00:26:38,000 --> 00:26:35,610 so what the point here is to show is 612 00:26:38,440 --> 00:26:38,010 that depending on which way we begin if 613 00:26:41,830 --> 00:26:38,450 it begin 614 00:26:43,870 --> 00:26:41,840 stagnant lid it's not super easy to get 615 00:26:45,550 --> 00:26:43,880 out again in plate tectonic village we 616 00:26:47,500 --> 00:26:45,560 can we can get into a one plate regime 617 00:26:59,700 --> 00:26:47,510 but it's very difficult to get back from 618 00:27:01,630 --> 00:26:59,710 them okay now it's time we go all right 619 00:27:06,700 --> 00:27:01,640 so quickly a couple of thought 620 00:27:09,100 --> 00:27:06,710 experiments so first one is what happens 621 00:27:10,870 --> 00:27:09,110 to reduce the heat production in earth a 622 00:27:13,180 --> 00:27:10,880 little bit by pelting it with rocks 623 00:27:14,980 --> 00:27:13,190 early so this is basically making the 624 00:27:20,200 --> 00:27:14,990 mantle temperature on average a little 625 00:27:21,580 --> 00:27:20,210 bit colder if we begin in this 626 00:27:26,650 --> 00:27:21,590 particular case if you begin with a 627 00:27:29,110 --> 00:27:26,660 condor it explan attends to want to be 628 00:27:32,140 --> 00:27:29,120 in a stagette lid regime and we reduce 629 00:27:33,610 --> 00:27:32,150 the amount of heat production an amount 630 00:27:35,230 --> 00:27:33,620 that corresponds to losing what is 631 00:27:38,770 --> 00:27:35,240 essentially to modern inventory of 632 00:27:40,870 --> 00:27:38,780 continental heat production there is a 633 00:27:46,690 --> 00:27:40,880 greater probability to end up in a 634 00:27:51,760 --> 00:27:46,700 multi-mode regime right so the early the 635 00:27:55,630 --> 00:27:51,770 early of a the early erosion of of Earth 636 00:27:59,260 --> 00:27:55,640 by rocks essentially by big rocks makes 637 00:28:00,610 --> 00:27:59,270 it more likely to end up in a regime 638 00:28:04,060 --> 00:28:00,620 where plate tectonics is it leaves 639 00:28:07,420 --> 00:28:04,070 possible we do the other experiments 640 00:28:09,010 --> 00:28:07,430 begin in this world and we began in a 641 00:28:10,270 --> 00:28:09,020 plate tectonic regime and we increase 642 00:28:12,940 --> 00:28:10,280 the heat production towards something 643 00:28:14,800 --> 00:28:12,950 like chondritic we're more likely to be 644 00:28:18,630 --> 00:28:14,810 in a stagnant later once or one play 645 00:28:21,280 --> 00:28:18,640 planet world so the idea here is that 646 00:28:24,190 --> 00:28:21,290 the style of stirring the choice of 647 00:28:26,550 --> 00:28:24,200 planet makes it depends in this case on 648 00:28:32,230 --> 00:28:26,560 what how strong the conductive stresses 649 00:28:34,320 --> 00:28:32,240 and that depends a bit on the 650 00:28:40,510 --> 00:28:34,330 collisional history early all right 651 00:28:42,280 --> 00:28:40,520 quick one I promise all right so next 652 00:28:44,230 --> 00:28:42,290 thing is what happens we take we so you 653 00:28:47,590 --> 00:28:44,240 know the the data set I showed the 654 00:28:49,510 --> 00:28:47,600 beginning this one basically said all 655 00:28:51,910 --> 00:28:49,520 right earth plenty of Earth's first 656 00:28:52,360 --> 00:28:51,920 three billion years certainly was 657 00:28:54,540 --> 00:28:52,370 dynamic 658 00:28:56,710 --> 00:28:54,550 be very active very time-dependent 659 00:28:58,690 --> 00:28:56,720 question is how resilient was Earth's 660 00:29:03,130 --> 00:28:58,700 climate through that period as Earth was 661 00:29:06,070 --> 00:29:03,140 figuring itself out as it was evolving 662 00:29:07,720 --> 00:29:06,080 to go back in time evolving from what we 663 00:29:10,060 --> 00:29:07,730 have sort of continuous plate tectonics 664 00:29:12,400 --> 00:29:10,070 something that looks more spasmodic what 665 00:29:15,570 --> 00:29:12,410 are the consequences one way to do this 666 00:29:19,299 --> 00:29:15,580 is to perturb a thermal history model so 667 00:29:21,340 --> 00:29:19,309 what this is is this is now this is back 668 00:29:23,350 --> 00:29:21,350 in time it's a thermal history history 669 00:29:24,790 --> 00:29:23,360 calculation for earth with some other 670 00:29:27,280 --> 00:29:24,800 stuff on it so the black line is the 671 00:29:29,080 --> 00:29:27,290 evolution of mantle temperature as we go 672 00:29:31,780 --> 00:29:29,090 back in time Earth's plates choose 673 00:29:34,600 --> 00:29:31,790 different shapes different platforms and 674 00:29:38,799 --> 00:29:34,610 the amount is the way in which it cools 675 00:29:41,080 --> 00:29:38,809 changes so black is did the temperature 676 00:29:43,180 --> 00:29:41,090 of the mantle the outgassing rates are 677 00:29:44,740 --> 00:29:43,190 in the heavy red line so the heavy line 678 00:29:47,710 --> 00:29:44,750 this is just assuming markers and 679 00:29:49,330 --> 00:29:47,720 solidus is right and the dash red line 680 00:29:51,250 --> 00:29:49,340 is assuming that marker Sherman solid is 681 00:29:54,160 --> 00:29:51,260 his right and his student Raj Das Gupta 682 00:29:56,500 --> 00:29:54,170 'he's outgassing efficiency is correct 683 00:29:59,020 --> 00:29:56,510 so outgassing changes back through time 684 00:30:00,610 --> 00:29:59,030 because d carbonation is better so we 685 00:30:01,900 --> 00:30:00,620 can choose a period perturb it so we 686 00:30:06,310 --> 00:30:01,910 take the mantle temperature and now 687 00:30:07,810 --> 00:30:06,320 introduce an episodic component to it we 688 00:30:10,660 --> 00:30:07,820 can ask the question what is the pco2 689 00:30:13,120 --> 00:30:10,670 that emerges from that bc 2 depends on 690 00:30:16,120 --> 00:30:13,130 the volcanic flux and the weathering 691 00:30:18,490 --> 00:30:16,130 regime the weathering rate not just show 692 00:30:19,419 --> 00:30:18,500 you a couple solutions and then i'll 693 00:30:23,080 --> 00:30:19,429 finish we're going to look at a couple 694 00:30:25,840 --> 00:30:23,090 plots that look like this so this is a 695 00:30:30,480 --> 00:30:25,850 zonal energy balance model and so you 696 00:30:39,010 --> 00:30:30,490 can look at greenhouse forcing all right 697 00:30:43,670 --> 00:30:41,390 alright so we're going to put ur bit and 698 00:30:45,920 --> 00:30:43,680 win a North Christine for ten seconds so 699 00:30:47,980 --> 00:30:45,930 the three to three different possible 700 00:30:50,990 --> 00:30:47,990 solutions ice-free snowball earth 701 00:30:52,430 --> 00:30:51,000 partially glaciated earth this is where 702 00:30:54,380 --> 00:30:52,440 we start if we introduce that 703 00:30:57,350 --> 00:30:54,390 perturbation and under current Earth's 704 00:31:00,200 --> 00:30:57,360 current mantle temperature as you can 705 00:31:01,820 --> 00:31:00,210 see as we go through the hot period we 706 00:31:03,140 --> 00:31:01,830 head towards an i3 earth we don't 707 00:31:05,000 --> 00:31:03,150 approach the green on green house run 708 00:31:07,400 --> 00:31:05,010 away does it go through the cold period 709 00:31:11,990 --> 00:31:07,410 we must make more glaciers not super 710 00:31:15,020 --> 00:31:12,000 interesting we go at 3.5 billion years 711 00:31:22,010 --> 00:31:15,030 the answer is potentially a lot more 712 00:31:25,460 --> 00:31:22,020 interesting being that at 3.5 billion 713 00:31:30,290 --> 00:31:25,470 years we entered we essentially begin in 714 00:31:32,540 --> 00:31:30,300 a frozen planet this is a 3.5 billion 715 00:31:34,460 --> 00:31:32,550 with beginning to frozen planet if we 716 00:31:36,170 --> 00:31:34,470 wanted to plant it up we can actually 717 00:31:37,520 --> 00:31:36,180 achieve partial glaciation could 718 00:31:39,740 --> 00:31:37,530 actually end up all the way up over here 719 00:31:41,210 --> 00:31:39,750 if we cool the planet back down when we 720 00:31:46,280 --> 00:31:41,220 just make a frozen planted a lot more 721 00:31:48,110 --> 00:31:46,290 frozen in the Precambrian world which 722 00:31:50,680 --> 00:31:48,120 has got it which is a water world the 723 00:31:53,750 --> 00:31:50,690 albedo is that mostly the water planet 724 00:31:57,380 --> 00:31:53,760 the interesting thing here is if we 725 00:32:00,050 --> 00:31:57,390 increase the outgassing or increase the 726 00:32:02,330 --> 00:32:00,060 outgassing or decrease the outgassing we 727 00:32:04,700 --> 00:32:02,340 never answer a pen glacial earth alright 728 00:32:07,070 --> 00:32:04,710 so precambrian world being warm at least 729 00:32:09,590 --> 00:32:07,080 with our our simulations is not a 730 00:32:12,800 --> 00:32:09,600 surprise it's been a few more than 10 731 00:32:15,770 --> 00:32:12,810 seconds yes okay all right just finish 732 00:32:18,110 --> 00:32:15,780 volatile cycling try to put too much 733 00:32:19,880 --> 00:32:18,120 into this but basically the crux is 734 00:32:23,200 --> 00:32:19,890 vample stirring how does in gassing and 735 00:32:26,690 --> 00:32:23,210 outgassing work how does it in turn make 736 00:32:27,770 --> 00:32:26,700 govern the atmospheric stability how 737 00:32:30,050 --> 00:32:27,780 does that affect the radiative 738 00:32:32,900 --> 00:32:30,060 properties of the atmosphere and what is 739 00:32:36,380 --> 00:32:32,910 the likelihood and duration of habitable 740 00:32:38,000 --> 00:32:36,390 periods in terms of earth we can bounce 741 00:32:41,750 --> 00:32:38,010 it and out of snowballs but we don't 742 00:32:43,460 --> 00:32:41,760 seem to do much more than that all right 743 00:32:46,590 --> 00:32:43,470 thank you all right let's thank our 744 00:32:50,740 --> 00:32:48,090 [Applause] 745 00:32:52,960 --> 00:32:50,750 so I guess we have a short time for 746 00:32:59,770 --> 00:32:52,970 questions and you can catch mark maybe 747 00:33:02,320 --> 00:32:59,780 at the poster and coffee breaks yes yes 748 00:33:05,320 --> 00:33:02,330 could you go back one slide please sure 749 00:33:07,000 --> 00:33:05,330 now that spot on the left is a little 750 00:33:09,280 --> 00:33:07,010 for example just the blue lines where we 751 00:33:11,560 --> 00:33:09,290 talked about snowball events now there's 752 00:33:14,590 --> 00:33:11,570 a lot more structure unless billion 753 00:33:16,600 --> 00:33:14,600 years then there is previously yes and I 754 00:33:18,730 --> 00:33:16,610 assume that that's a selection effect 755 00:33:20,500 --> 00:33:18,740 but can you make any comments about that 756 00:33:22,150 --> 00:33:20,510 for example of that what's called the 757 00:33:24,370 --> 00:33:22,160 boring billion I guess what is nothing 758 00:33:25,870 --> 00:33:24,380 there now did a lot happen and we just 759 00:33:30,480 --> 00:33:25,880 can't see it because of selection of X 760 00:33:36,610 --> 00:33:32,740 well I don't think you'd get away from 761 00:33:37,840 --> 00:33:36,620 the problem of selection or bias as you 762 00:33:43,750 --> 00:33:37,850 go back to the archaean because I love 763 00:33:46,290 --> 00:33:43,760 rocks around however in the rotten in 764 00:33:48,880 --> 00:33:46,300 the ark any exposed archaean rocks 765 00:33:51,640 --> 00:33:48,890 proterozoic and are key and rocks to be 766 00:33:53,290 --> 00:33:51,650 in years and before there's only one 767 00:33:55,630 --> 00:33:53,300 period this one a particular that has 768 00:34:01,420 --> 00:33:55,640 reliable glacial deposits in it snowdrop 769 00:34:04,000 --> 00:34:01,430 stones no evidence of cap carbonate like 770 00:34:06,040 --> 00:34:04,010 sequences that are that are common that 771 00:34:09,060 --> 00:34:06,050 a common indicators of rapid melt you 772 00:34:12,250 --> 00:34:09,070 know melt outs from snowball solutions 773 00:34:15,000 --> 00:34:12,260 but to know there are no reliable 774 00:34:18,100 --> 00:34:15,010 glacial glacial features in any rocks 775 00:34:19,870 --> 00:34:18,110 certainly before I mean this guy is 776 00:34:24,520 --> 00:34:19,880 hotly contested this is paul Hoffman's 777 00:34:26,110 --> 00:34:24,530 figure before 2.5 is you know basically 778 00:34:29,500 --> 00:34:26,120 all glacial features before that are 779 00:34:31,240 --> 00:34:29,510 questions into Bay right but it look 780 00:34:32,770 --> 00:34:31,250 could it be lots and lots and lots of 781 00:34:34,750 --> 00:34:32,780 structure there as much on the right 782 00:34:39,820 --> 00:34:34,760 side of this plot is on the left no no 783 00:34:43,360 --> 00:34:39,830 no so to produce this these two periods 784 00:34:45,160 --> 00:34:43,370 took lots and lots of Matt you know you 785 00:34:46,960 --> 00:34:45,170 know first you have to identify all the 786 00:34:49,180 --> 00:34:46,970 rocks from the planets that are within 787 00:34:51,760 --> 00:34:49,190 that age group in there and Mackenzie 788 00:34:53,890 --> 00:34:51,770 mountains in Canada in Africa and in 789 00:34:57,690 --> 00:34:53,900 Australia and in those the question you 790 00:34:59,880 --> 00:34:57,700 ask is what is the aerial fraction that 791 00:35:02,880 --> 00:34:59,890 cords evidence of notches glaciers but 792 00:35:04,650 --> 00:35:02,890 rapid deglaciation you have to be able 793 00:35:08,760 --> 00:35:04,660 to demonstrate that the glaciation was 794 00:35:10,530 --> 00:35:08,770 also at the equator and there's 795 00:35:11,640 --> 00:35:10,540 directional paleo magnetic data here 796 00:35:16,770 --> 00:35:11,650 that allows you to do that more 797 00:35:18,930 --> 00:35:16,780 convincingly but there's lots of rocks 798 00:35:21,690 --> 00:35:18,940 that is thought to be at high latitude 799 00:35:27,540 --> 00:35:21,700 at this at these periods with no 800 00:35:30,180 --> 00:35:27,550 evidence of glaciation okay not true I'm 801 00:35:32,640 --> 00:35:30,190 not going to make dumb but I'm spouting 802 00:35:42,270 --> 00:35:32,650 the party line that so not true what is 803 00:35:45,180 --> 00:35:42,280 your this one is yes I'm not argh so I'm 804 00:35:47,550 --> 00:35:45,190 not arguing at 2.3 you said the whole 805 00:35:50,579 --> 00:35:47,560 thing wasn't not another potential one 806 00:35:53,900 --> 00:35:50,589 at 3.5 that Martian do it published 807 00:35:56,370 --> 00:35:53,910 about a year ago very clear drop stones 808 00:35:58,500 --> 00:35:56,380 no evidence of the camp but we don't 809 00:36:00,690 --> 00:35:58,510 really know if the camp carbonate would 810 00:36:03,260 --> 00:36:00,700 form under the conditions of an archaeon 811 00:36:06,690 --> 00:36:03,270 ocean the chemistry is different I 812 00:36:08,910 --> 00:36:06,700 chemistry is different so but so the 813 00:36:10,980 --> 00:36:08,920 drop stones there are there is there is 814 00:36:15,089 --> 00:36:10,990 what looks like a good glacial thing in 815 00:36:19,520 --> 00:36:15,099 the Barbican at about 3.5 clear drop 816 00:36:23,579 --> 00:36:19,530 stones barbed units no striated doubles 817 00:36:26,160 --> 00:36:23,589 but you don't always get those true 818 00:36:27,540 --> 00:36:26,170 enough but we don't see is continuous 819 00:36:30,630 --> 00:36:27,550 evidence of glaciation all the way 820 00:36:33,569 --> 00:36:30,640 through this period but even partial but 821 00:36:36,450 --> 00:36:33,579 you know the record is not commensurate 822 00:36:38,790 --> 00:36:36,460 to that full stop we don't have a 823 00:36:46,339 --> 00:36:38,800 continuous record of our key in time the 824 00:36:58,970 --> 00:36:46,349 way we do with a finer look good when I 825 00:37:06,690 --> 00:37:03,569 okay baby I mean if you'd like to 826 00:37:09,450 --> 00:37:06,700 discuss a Grover but is no percentage of 827 00:37:11,480 --> 00:37:09,460 our TM specifically they are changing 828 00:37:14,450 --> 00:37:11,490 all to occupy only 20 829 00:37:17,510 --> 00:37:14,460 % of another continent and if we go back 830 00:37:20,000 --> 00:37:17,520 ari Eric Ian it's a distant one percent 831 00:37:22,330 --> 00:37:20,010 but I'm not arguing with that but so the 832 00:37:24,560 --> 00:37:22,340 model solutions that that we have 833 00:37:25,609 --> 00:37:24,570 admitted partial glaciation through the 834 00:37:27,830 --> 00:37:25,619 hope through that whole theory about 835 00:37:29,650 --> 00:37:27,840 their product is positive at least one 836 00:37:32,240 --> 00:37:29,660 oh yeah I wouldn't argue that there's 837 00:37:34,270 --> 00:37:32,250 the surprising thing in its period is it 838 00:37:37,730 --> 00:37:34,280 is not global glaciation the whole time 839 00:37:40,340 --> 00:37:37,740 right so if i did a climate model 840 00:37:42,500 --> 00:37:40,350 without considering the geodynamic 841 00:37:44,660 --> 00:37:42,510 control on volcanic outgassing and 842 00:37:46,130 --> 00:37:44,670 weathering we would have us we would 843 00:37:47,930 --> 00:37:46,140 have a snowball solution for the first 844 00:37:50,900 --> 00:37:47,940 billion years of Earth's life if I 845 00:37:52,820 --> 00:37:50,910 include weathering and now casting at 846 00:37:54,620 --> 00:37:52,830 this controlled by mantle stirring we 847 00:37:56,180 --> 00:37:54,630 get partial I solutions and I don't 848 00:38:05,480 --> 00:37:56,190 think that's inconsistent with either of 849 00:38:08,390 --> 00:38:05,490 the two comments all right any more 850 00:38:12,680 --> 00:38:08,400 questions we seem to still have a bit of 851 00:38:14,270 --> 00:38:12,690 time but all right well then we'll go 852 00:38:18,270 --> 00:38:14,280 ahead and move on to the next Hut thank