1 00:00:05,780 --> 00:00:03,619 good morning everyone if you're in the 2 00:00:07,700 --> 00:00:05,790 name time zone and good afternoon if 3 00:00:10,430 --> 00:00:07,710 you're in a p.m. time zone welcome to 4 00:00:13,820 --> 00:00:10,440 the new season of the NAI director's 5 00:00:17,480 --> 00:00:13,830 seminar I am really really pleased that 6 00:00:20,720 --> 00:00:17,490 we can kick off the seminar series this 7 00:00:23,090 --> 00:00:20,730 year I I feel think as an academic 8 00:00:25,939 --> 00:00:23,100 obviously the year starts in September 9 00:00:27,740 --> 00:00:25,949 but then again the federal fiscal year 10 00:00:29,750 --> 00:00:27,750 starts in October so we're pretty close 11 00:00:31,460 --> 00:00:29,760 to that too so whatever new year you 12 00:00:33,560 --> 00:00:31,470 want we've got it and Rosh Hashanah the 13 00:00:35,959 --> 00:00:33,570 Jewish New Year is coming up so it's new 14 00:00:38,959 --> 00:00:35,969 year all the way around so at any rate 15 00:00:41,510 --> 00:00:38,969 it's a real pleasure to have norm sleep 16 00:00:45,619 --> 00:00:41,520 with us he's right here at nai central 17 00:00:48,380 --> 00:00:45,629 to present this morning seminar norm as 18 00:00:50,840 --> 00:00:48,390 I think most of you know is a professor 19 00:00:53,869 --> 00:00:50,850 of geophysics at Stanford University he 20 00:00:55,910 --> 00:00:53,879 is a very very distinguished member of 21 00:00:57,410 --> 00:00:55,920 the science community and the DNA I he's 22 00:01:00,349 --> 00:00:57,420 a member of the National Academy of 23 00:01:02,029 --> 00:01:00,359 Sciences he's a fellow of most of the 24 00:01:04,640 --> 00:01:02,039 professional societies that you can 25 00:01:06,080 --> 00:01:04,650 think of the triple-a s the Geological 26 00:01:08,899 --> 00:01:06,090 Society of America and the American 27 00:01:13,719 --> 00:01:08,909 Geophysical Union he's won a fistful of 28 00:01:17,690 --> 00:01:13,729 medals I won't try to list them all his 29 00:01:20,990 --> 00:01:17,700 educational background includes Michigan 30 00:01:24,560 --> 00:01:21,000 State and then masters and PhD in 31 00:01:27,050 --> 00:01:24,570 geophysics from MIT and norm is going to 32 00:01:29,420 --> 00:01:27,060 be speaking with us this morning about a 33 00:01:31,910 --> 00:01:29,430 topic that he's been working on lately 34 00:01:34,520 --> 00:01:31,920 and talked about it apps icon which is 35 00:01:36,859 --> 00:01:34,530 the habitability of super Earths many of 36 00:01:39,260 --> 00:01:36,869 which we anticipate discovering in the 37 00:01:43,840 --> 00:01:39,270 next few years in norm take it away 38 00:01:48,560 --> 00:01:43,850 ok the interest in superest comes about 39 00:01:50,749 --> 00:01:48,570 simply some sciences like the drunk 40 00:01:53,929 --> 00:01:50,759 looking for lost car keys that looks 41 00:01:56,510 --> 00:01:53,939 under the lamppost where it can see we 42 00:01:59,060 --> 00:01:56,520 obviously have a sampling bias of when 43 00:02:02,420 --> 00:01:59,070 you find silicate planets around another 44 00:02:07,690 --> 00:02:02,430 star we're going to be more to find 45 00:02:10,070 --> 00:02:07,700 large ones and small ones the tectonics 46 00:02:13,290 --> 00:02:10,080 especially if we can concentrate on what 47 00:02:15,630 --> 00:02:13,300 may be observable at a distant 48 00:02:19,200 --> 00:02:15,640 and the have ability of these objects 49 00:02:22,710 --> 00:02:19,210 are of interest we have the Earth and 50 00:02:27,420 --> 00:02:22,720 Mars a small silicate planet to provide 51 00:02:30,450 --> 00:02:27,430 at least some analogy in comparison okay 52 00:02:33,990 --> 00:02:30,460 they're basically three things you need 53 00:02:37,680 --> 00:02:34,000 in the recipe for habitability you can't 54 00:02:39,720 --> 00:02:37,690 be too hot or too cold especially if we 55 00:02:42,960 --> 00:02:39,730 consider habitability that can be 56 00:02:46,920 --> 00:02:42,970 observed at a distance we have to have 57 00:02:49,620 --> 00:02:46,930 Rock cycles that are active so we don't 58 00:02:52,050 --> 00:02:49,630 end up with Mars were essentially all 59 00:02:55,080 --> 00:02:52,060 the volatile mats are in the subsurface 60 00:02:59,340 --> 00:02:55,090 are Venus why they're all in the 61 00:03:03,150 --> 00:02:59,350 atmosphere and we need some sort of 62 00:03:15,680 --> 00:03:03,160 chemical disequilibrium so the biota can 63 00:03:19,770 --> 00:03:15,690 have lunch okay what is bad provide 64 00:03:23,580 --> 00:03:19,780 concentrating on super earth we can end 65 00:03:26,970 --> 00:03:23,590 up creating too much nother or gas this 66 00:03:29,580 --> 00:03:26,980 is detectable particularly in transit 67 00:03:33,090 --> 00:03:29,590 we have Neptune as example in our own 68 00:03:38,370 --> 00:03:33,100 solar system we can also get too close 69 00:03:42,420 --> 00:03:38,380 to the star Venus as an example we can 70 00:03:45,510 --> 00:03:42,430 get outside the habitable zone this kind 71 00:03:49,140 --> 00:03:45,520 of renders the object uninhabitable at 72 00:03:51,720 --> 00:03:49,150 the surface but probably habitable in 73 00:03:53,570 --> 00:03:51,730 the subsurface it just becomes hard to 74 00:03:57,090 --> 00:03:53,580 detect 75 00:04:08,250 --> 00:03:57,100 traditionally uninhabitable but non 76 00:04:11,699 --> 00:04:08,260 traditionally habitable what else is bad 77 00:04:13,920 --> 00:04:11,709 we need geochemical cycles as I've 78 00:04:18,320 --> 00:04:13,930 already mentioned and Garr concentrate 79 00:04:22,710 --> 00:04:18,330 us on on the talk Mars is something 80 00:04:25,050 --> 00:04:22,720 where this has happened asteroid impacts 81 00:04:26,310 --> 00:04:25,060 occur infrequently but they can spoil 82 00:04:28,560 --> 00:04:26,320 your day 83 00:04:31,290 --> 00:04:28,570 and we can end up with a planet-wide 84 00:04:33,270 --> 00:04:31,300 ocean which I'll discuss also we can end 85 00:04:36,660 --> 00:04:33,280 up with water world and I'll show this 86 00:04:39,420 --> 00:04:36,670 it's a probable fate of a super earth I 87 00:04:44,580 --> 00:04:39,430 can get different life than on the earth 88 00:04:47,280 --> 00:04:44,590 but not necessarily die up okay we've 89 00:04:51,840 --> 00:04:47,290 had a couple papers recently on plate 90 00:04:55,820 --> 00:04:51,850 tectonics and super earth balance eeeh - 91 00:05:00,140 --> 00:04:55,830 all included it was likely O'Neill 92 00:05:05,040 --> 00:05:00,150 Lonardo concluded it was highly unlikely 93 00:05:08,550 --> 00:05:05,050 I'm going to simplify the math and the 94 00:05:11,100 --> 00:05:08,560 derivations things become a nominally 95 00:05:13,770 --> 00:05:11,110 simple if you use gravity rather than 96 00:05:16,200 --> 00:05:13,780 mass as a scaling power you don't have 97 00:05:19,560 --> 00:05:16,210 to carry around mass to all kinds of 98 00:05:24,810 --> 00:05:19,570 fractional powers I'm going to derive 99 00:05:28,470 --> 00:05:24,820 both the Valencia and Lennar Dec neon 100 00:05:30,630 --> 00:05:28,480 Antarctic results some others I'm going 101 00:05:34,110 --> 00:05:30,640 to illustrate the assumptions I'm going 102 00:05:37,650 --> 00:05:34,120 to avoid tidally heated planets there 103 00:05:39,840 --> 00:05:37,660 was a paper on this at UPS icon but 104 00:05:43,820 --> 00:05:39,850 tides are going to make the fire - 105 00:05:47,010 --> 00:05:43,830 inside hotter and more vigorous probably 106 00:05:49,680 --> 00:05:47,020 possibly lead to abundant surface 107 00:05:56,010 --> 00:05:49,690 volcanism which will also give us 108 00:05:59,880 --> 00:05:56,020 geochemical cycles okay if we use 109 00:06:03,120 --> 00:05:59,890 gravity as a size parameter we use 110 00:06:06,950 --> 00:06:03,130 Gauss's law we have the other advantage 111 00:06:10,800 --> 00:06:06,960 is that gravity for large planets scales 112 00:06:15,720 --> 00:06:10,810 to the square root rather than cube root 113 00:06:17,700 --> 00:06:15,730 of mass so a ton earth-mass planet will 114 00:06:21,210 --> 00:06:17,710 have about three times the gravity of 115 00:06:23,490 --> 00:06:21,220 the earth Mars which is about 1/10 116 00:06:26,190 --> 00:06:23,500 Earth's mass planet will have about 4 117 00:06:28,320 --> 00:06:26,200 tenths so we have a parameter that for 118 00:06:32,480 --> 00:06:28,330 the range of planets that we consider 119 00:06:35,660 --> 00:06:32,490 habitable it's not going to vary a lot 120 00:06:38,719 --> 00:06:35,670 this will also lead to some 121 00:06:48,589 --> 00:06:43,519 okay we have God's us law for gravity 122 00:06:54,529 --> 00:06:48,599 the gravitational flux from an object 123 00:06:58,079 --> 00:06:54,539 getting longer or not it is it is not as 124 00:07:02,489 --> 00:06:58,089 equal to four times G times the mass of 125 00:07:06,269 --> 00:07:02,499 the planet the equilibrium Heat fall has 126 00:07:08,489 --> 00:07:06,279 the same type of formula the equilibrium 127 00:07:11,909 --> 00:07:08,499 heat flow is a minimum heat flow an 128 00:07:16,829 --> 00:07:11,919 object can have where it will cool down 129 00:07:19,980 --> 00:07:16,839 rather than heat up planet during its 130 00:07:23,909 --> 00:07:19,990 history can only cool a few hundred K 131 00:07:26,699 --> 00:07:23,919 from a dream a hot and basically Cawley 132 00:07:30,689 --> 00:07:26,709 Maldon at the surface where it's too 133 00:07:33,779 --> 00:07:30,699 cold for having any serious tectonics so 134 00:07:36,449 --> 00:07:33,789 a heat wall being crudely imbalanced 135 00:07:40,320 --> 00:07:36,459 with radioactivity is something that 136 00:07:47,279 --> 00:07:40,330 will give us a scaling assumption and we 137 00:07:52,279 --> 00:07:47,289 can combine these and get the 138 00:07:55,670 --> 00:07:52,289 radioactive eath wall it's again 139 00:08:01,259 --> 00:07:55,680 depending on the mass of the planet and 140 00:08:04,469 --> 00:08:01,269 we have something that's observable for 141 00:08:07,949 --> 00:08:04,479 the earth gravity for an object if we 142 00:08:14,519 --> 00:08:07,959 can determine about the size diameter is 143 00:08:16,769 --> 00:08:14,529 observable and the balance here will 144 00:08:20,519 --> 00:08:16,779 reflect a long-lasting state of the 145 00:08:23,369 --> 00:08:20,529 planet that the planet cools extremely 146 00:08:25,649 --> 00:08:23,379 fast at during and after accretion feels 147 00:08:29,029 --> 00:08:25,659 extremely fast anytime wound farming 148 00:08:31,829 --> 00:08:29,039 impact but cool slowly at that kind of 149 00:08:35,939 --> 00:08:31,839 50 hundred pay four billion years of 150 00:08:38,120 --> 00:08:35,949 that order and has a crude balance 151 00:08:41,730 --> 00:08:38,130 between heat flow and review activity 152 00:08:44,309 --> 00:08:41,740 observe is long-lasting and if we look 153 00:08:47,250 --> 00:08:44,319 at a random planet we're going to see it 154 00:08:51,300 --> 00:08:47,260 in its long lasting state rather than 155 00:08:55,150 --> 00:08:51,310 the state that is in relatively briefly 156 00:08:58,320 --> 00:08:55,160 okay we get some simple scaling formulas 157 00:09:02,830 --> 00:08:58,330 out of this let the static pressure 158 00:09:05,110 --> 00:09:02,840 caprices a personal to gravity density 159 00:09:07,240 --> 00:09:05,120 this is the near surface density it's 160 00:09:11,050 --> 00:09:07,250 not going to very much for silicate 161 00:09:15,070 --> 00:09:11,060 planets the geothermal ative to the 162 00:09:19,320 --> 00:09:15,080 surface temperature is proportional to 163 00:09:22,120 --> 00:09:19,330 the heat wall from the planet and hence 164 00:09:25,810 --> 00:09:22,130 proportional to the deep fall from 165 00:09:28,270 --> 00:09:25,820 radioactivity again increases with depth 166 00:09:30,730 --> 00:09:28,280 and is inversely proportional 167 00:09:33,670 --> 00:09:30,740 conductivity this is a rock property 168 00:09:35,560 --> 00:09:33,680 that's not going to very much the 169 00:09:39,010 --> 00:09:35,570 surface temperature if we stick the 170 00:09:43,620 --> 00:09:39,020 palatable planets is not far from the 171 00:09:52,380 --> 00:09:43,630 freezing point of water and we can write 172 00:09:56,320 --> 00:09:52,390 the geothermal in terms of pressure and 173 00:10:00,130 --> 00:09:56,330 this means that if we plot things as a 174 00:10:01,780 --> 00:10:00,140 petrology pressure temperature gia firm 175 00:10:04,690 --> 00:10:01,790 is going to be to the first order 176 00:10:07,150 --> 00:10:04,700 invariant for planetary site if you have 177 00:10:10,000 --> 00:10:07,160 a pressure temperature geothermal earth 178 00:10:12,730 --> 00:10:10,010 it will work on Mars and we'll work on 179 00:10:14,290 --> 00:10:12,740 the super earth to the first order it 180 00:10:16,300 --> 00:10:14,300 will depend on the amount of 181 00:10:18,460 --> 00:10:16,310 radioactivity in the planet which will 182 00:10:22,390 --> 00:10:18,470 of course decrease as it's used up 183 00:10:24,700 --> 00:10:22,400 during its history but if we got a 184 00:10:27,100 --> 00:10:24,710 particular point in the evolution of a 185 00:10:31,050 --> 00:10:27,110 planet we have the same pressure 186 00:10:39,700 --> 00:10:35,500 okay we get other useful scalings from 187 00:10:44,980 --> 00:10:39,710 this the pressure at the base of all put 188 00:10:47,620 --> 00:10:44,990 the sphere early the maximum depth of 189 00:10:51,180 --> 00:10:47,630 the planet is dominated the junction is 190 00:10:57,700 --> 00:10:51,190 going to be invariant of planetary size 191 00:11:00,880 --> 00:10:57,710 we have a on the plot here we have a 192 00:11:03,170 --> 00:11:00,890 temperature pressure grid for the 193 00:11:06,290 --> 00:11:03,180 melding of basalt 194 00:11:09,440 --> 00:11:06,300 the f we have a given temperature in the 195 00:11:12,280 --> 00:11:09,450 interior the pressure we're melding 196 00:11:15,580 --> 00:11:12,290 starts is going to be invariant of 197 00:11:19,640 --> 00:11:15,590 planetary size a big super-earth may be 198 00:11:22,130 --> 00:11:19,650 hotter we put in a hotter finger and 199 00:11:24,860 --> 00:11:22,140 we'll get melting at a greater depth and 200 00:11:27,790 --> 00:11:24,870 more total melting the points B and C 201 00:11:31,100 --> 00:11:27,800 are the points where the total amount 202 00:11:34,330 --> 00:11:31,110 melt generated in a column equals the 203 00:11:37,070 --> 00:11:34,340 depth and that will be the depth of the 204 00:11:40,130 --> 00:11:37,080 top of the model of the base of the 205 00:11:43,700 --> 00:11:40,140 ocean crust if we plot anything else 206 00:11:47,960 --> 00:11:43,710 here that's pressure dependent thickness 207 00:11:52,690 --> 00:11:47,970 of oceanic crust depends on the pressure 208 00:11:58,190 --> 00:11:52,700 of where melting starts and hence will 209 00:12:00,950 --> 00:11:58,200 scale inversely with gravity thickness 210 00:12:04,070 --> 00:12:00,960 of continental crust the driving forces 211 00:12:13,360 --> 00:12:04,080 will see later to make top metal crust 212 00:12:15,770 --> 00:12:13,370 from the ridge will scale such that the 213 00:12:17,840 --> 00:12:15,780 thickness of continental crust will 214 00:12:20,480 --> 00:12:17,850 scale with the thickness of lettuce fare 215 00:12:23,630 --> 00:12:20,490 the segments of hydrothermally altered 216 00:12:29,660 --> 00:12:23,640 crusts scales with the pressure to close 217 00:12:32,270 --> 00:12:29,670 cracks and if we plot a collinear with 218 00:12:36,710 --> 00:12:32,280 the zone of hydrothermal alteration the 219 00:12:38,660 --> 00:12:36,720 salted crust the depleted mantle of 220 00:12:42,650 --> 00:12:38,670 melts heavily and the base of the 221 00:12:45,020 --> 00:12:42,660 lithosphere that diagram at a given 222 00:12:48,500 --> 00:12:45,030 interior temperature will be in varying 223 00:12:50,570 --> 00:12:48,510 the private area size though what we 224 00:12:53,690 --> 00:12:50,580 learned about the earth carries through 225 00:12:57,350 --> 00:12:53,700 one caveat is that the super earth in 226 00:12:59,780 --> 00:12:57,360 the interior may be hotter but then it 227 00:13:01,850 --> 00:12:59,790 will be like the earth early in its 228 00:13:06,290 --> 00:13:01,860 history when the interior is hotter we 229 00:13:12,170 --> 00:13:06,300 get good analogy here and we learn a lot 230 00:13:15,679 --> 00:13:12,180 fairly quick there's a socket scaling 231 00:13:17,600 --> 00:13:15,689 here that's even more universal 232 00:13:19,249 --> 00:13:17,610 the cool material you'll have to 233 00:13:22,519 --> 00:13:19,259 circulate it through the thermal 234 00:13:27,019 --> 00:13:22,529 boundary layer go let the spirit this is 235 00:13:29,419 --> 00:13:27,029 true of any large convective object the 236 00:13:32,329 --> 00:13:29,429 scaling with another proportionality 237 00:13:34,460 --> 00:13:32,339 constant would be true if we had a 238 00:13:37,460 --> 00:13:34,470 volcanic Li cold planet where the 239 00:13:41,150 --> 00:13:37,470 material erupts it has to a rough the 240 00:13:43,009 --> 00:13:41,160 cool we lose all the heat rather than 241 00:13:45,859 --> 00:13:43,019 just some in the lithosphere so there's 242 00:13:50,299 --> 00:13:45,869 a different proportionality constant so 243 00:13:53,329 --> 00:13:50,309 this time to circulate material form 244 00:13:56,030 --> 00:13:53,339 continental crust circulate material 245 00:13:58,840 --> 00:13:56,040 through the ridge axis where we know how 246 00:14:02,299 --> 00:13:58,850 material end up in the ocean crust 247 00:14:07,759 --> 00:14:02,309 produced enough volatile to recycle the 248 00:14:10,069 --> 00:14:07,769 ocean take material through the 249 00:14:13,009 --> 00:14:10,079 reservoir that forms hydrothermally 250 00:14:16,729 --> 00:14:13,019 altered crust all of this is invariant 251 00:14:19,909 --> 00:14:16,739 of planetary size and this is variance 252 00:14:23,449 --> 00:14:19,919 will depend on the cooling mechanism but 253 00:14:26,389 --> 00:14:23,459 is again there and we're dealing here 254 00:14:29,960 --> 00:14:26,399 with circulating material through the 255 00:14:32,749 --> 00:14:29,970 lithosphere the current scale time being 256 00:14:36,259 --> 00:14:32,759 couple billion years for the earth the 257 00:14:41,619 --> 00:14:36,269 scale time for anything else being the 258 00:14:49,579 --> 00:14:45,019 okay we need now to consider the 259 00:14:54,009 --> 00:14:49,589 tectonic mechanism any of our jobs it 260 00:14:57,019 --> 00:14:54,019 has to cool by conduct by convection 261 00:15:01,340 --> 00:14:57,029 conduction can dominate near the surface 262 00:15:05,359 --> 00:15:01,350 but the interior is simply too big to 263 00:15:11,650 --> 00:15:05,369 call over the regional age of the planet 264 00:15:15,799 --> 00:15:11,660 don't let CEA's group she balances 265 00:15:20,059 --> 00:15:15,809 matter wide forces it shows these are 266 00:15:22,879 --> 00:15:20,069 greater than the lithospheric forces and 267 00:15:25,129 --> 00:15:22,889 hence will have convection where it's 268 00:15:28,850 --> 00:15:25,139 controlled by the rate subscribe to 269 00:15:31,040 --> 00:15:28,860 think in the mantle O'Neill and on our 270 00:15:35,240 --> 00:15:31,050 cab models that effectively consider 271 00:15:38,620 --> 00:15:35,250 only forces in the lithosphere even 272 00:15:41,720 --> 00:15:38,630 though they're complicated and I show 273 00:15:46,760 --> 00:15:41,730 analytically that we can get into a 274 00:15:50,690 --> 00:15:46,770 state where plate tectonics only occurs 275 00:15:53,000 --> 00:15:50,700 in the on earth sized planets I'm going 276 00:15:54,640 --> 00:15:53,010 to again use gravity I'm going to derive 277 00:15:57,380 --> 00:15:54,650 results and going to illustrate 278 00:16:00,890 --> 00:15:57,390 assumptions and I got to come up with a 279 00:16:04,760 --> 00:16:00,900 displease result that were too ignorant 280 00:16:07,670 --> 00:16:04,770 of the earth to fully extrapolate regard 281 00:16:10,010 --> 00:16:07,680 come up with a pleasing result now if we 282 00:16:12,920 --> 00:16:10,020 don't have plate tectonics the interior 283 00:16:15,080 --> 00:16:12,930 is quite hot we'll still get lots of 284 00:16:19,090 --> 00:16:15,090 optimism will get geochemical cycles 285 00:16:22,250 --> 00:16:19,100 this will affect details but will not 286 00:16:27,530 --> 00:16:22,260 affect the fact that we have a Geo 287 00:16:30,890 --> 00:16:27,540 chemically active climate ok the heat 288 00:16:34,340 --> 00:16:30,900 flow through the lithosphere depends on 289 00:16:36,020 --> 00:16:34,350 this square root of plate by H law it 290 00:16:39,200 --> 00:16:36,030 depends on the temperature contrast 291 00:16:41,960 --> 00:16:39,210 across the lithosphere which will vary 292 00:16:44,360 --> 00:16:41,970 some but not a lot again because the 293 00:16:47,870 --> 00:16:44,370 planet is too cold we don't get sent 294 00:16:51,760 --> 00:16:47,880 Onix if the planet is too hot it cools 295 00:16:55,520 --> 00:16:51,770 extremely rapidly with a molten surface 296 00:16:57,890 --> 00:16:55,530 conductivity thermal diffusivity in the 297 00:17:01,580 --> 00:16:57,900 square root or material properties and 298 00:17:06,920 --> 00:17:01,590 we can write this dimensionally taking 299 00:17:09,020 --> 00:17:06,930 the term in the bracket to be the scale 300 00:17:11,270 --> 00:17:09,030 thickness of the lettuce fair and just 301 00:17:15,189 --> 00:17:11,280 getting the simple Fourier conduction 302 00:17:21,340 --> 00:17:19,090 okay to get subduction to go we have to 303 00:17:25,359 --> 00:17:21,350 have three things to work the slab has 304 00:17:28,059 --> 00:17:25,369 to bend with strains of order one the 305 00:17:30,460 --> 00:17:28,069 front megathrust the boundary between 306 00:17:33,789 --> 00:17:30,470 the slab and the are cast is leather 307 00:17:37,060 --> 00:17:33,799 sometimes slips and great soon tsunami 308 00:17:39,909 --> 00:17:37,070 earthquake so I can Sumatra I have slept 309 00:17:42,729 --> 00:17:39,919 one way or the other and the slab has to 310 00:17:45,879 --> 00:17:42,739 be able to kind of treat into the mouth 311 00:17:47,549 --> 00:17:45,889 and we don't really know on the earth 312 00:17:50,049 --> 00:17:47,559 which one of these is the rate-limiting 313 00:17:58,180 --> 00:17:50,059 process we know that all three have to 314 00:18:03,310 --> 00:17:58,190 occur okay to bend the slab simple way 315 00:18:05,830 --> 00:18:03,320 to model this is that we have a yield 316 00:18:07,720 --> 00:18:05,840 stress and a yield stress that acts over 317 00:18:10,299 --> 00:18:07,730 the thickness of the lithosphere and 318 00:18:12,879 --> 00:18:10,309 there has to be enough forces either 319 00:18:15,970 --> 00:18:12,889 from the buoyancy of the ridge axis or 320 00:18:23,739 --> 00:18:15,980 the negative buoyancy of the slab to 321 00:18:26,830 --> 00:18:23,749 allow this process to occur we also have 322 00:18:29,789 --> 00:18:26,840 subduction this depends on friction and 323 00:18:33,999 --> 00:18:29,799 it depends on friction thats related 324 00:18:37,779 --> 00:18:34,009 will coefficient of friction we know the 325 00:18:40,180 --> 00:18:37,789 coefficient friction of in fact rock we 326 00:18:43,899 --> 00:18:40,190 don't know the water crunch or piece of 327 00:18:47,320 --> 00:18:43,909 WF depth and I collected firms in here 328 00:18:52,060 --> 00:18:47,330 use that the pressure the lithostatic 329 00:18:55,119 --> 00:18:52,070 pressure is going to scale with depth 330 00:18:57,430 --> 00:18:55,129 and the scale thickness that this is 331 00:19:00,840 --> 00:18:57,440 going to act at is the scale thickness 332 00:19:05,499 --> 00:19:00,850 of the lithosphere and it's going to 333 00:19:07,899 --> 00:19:05,509 depend on gravity linearly the big point 334 00:19:10,889 --> 00:19:07,909 here is we don't know what the water 335 00:19:14,979 --> 00:19:10,899 pressure is so we don't know what this 336 00:19:26,440 --> 00:19:14,989 apparent coefficient of friction is new 337 00:19:34,990 --> 00:19:26,450 apparent ok we can solve 338 00:19:39,100 --> 00:19:35,000 for a driving force here the we have a 339 00:19:42,040 --> 00:19:39,110 driving force that's going to be 340 00:19:45,370 --> 00:19:42,050 proportional to the buoyancy of the slab 341 00:19:47,410 --> 00:19:45,380 a buoyancy of the ridge axis is going to 342 00:19:49,660 --> 00:19:47,420 be proportional temperature contrast 343 00:19:52,000 --> 00:19:49,670 proportional gravity proportional to 344 00:19:55,240 --> 00:19:52,010 thermal contraction coefficient I'm 345 00:19:57,400 --> 00:19:55,250 going to derive this on a later side 346 00:19:58,510 --> 00:19:57,410 that this is the classical Ridge push 347 00:20:02,050 --> 00:19:58,520 force 348 00:20:04,840 --> 00:20:02,060 buoyant material if it's not cannot 349 00:20:08,380 --> 00:20:04,850 sustain stressful but like the food I 350 00:20:11,110 --> 00:20:08,390 boil over water and we're assuming that 351 00:20:14,530 --> 00:20:11,120 this buoyancy force for the ridge is 352 00:20:17,590 --> 00:20:14,540 driving subduction if we solve this 353 00:20:21,100 --> 00:20:17,600 equation all the material parameters 354 00:20:23,050 --> 00:20:21,110 drop everything drops out except the 355 00:20:26,080 --> 00:20:23,060 temperature contrasts across the 356 00:20:28,510 --> 00:20:26,090 lithosphere the apparent coefficient of 357 00:20:30,670 --> 00:20:28,520 friction and the thermal expansion 358 00:20:33,700 --> 00:20:30,680 coefficient we're trying to get a 359 00:20:36,430 --> 00:20:33,710 numerical model this way we have to tune 360 00:20:41,230 --> 00:20:36,440 the numerical model which Armijo and an 361 00:20:43,240 --> 00:20:41,240 Arctic dead we cannot solve for the 362 00:20:46,320 --> 00:20:43,250 lettuce Pyrrhic thickness is a function 363 00:20:48,760 --> 00:20:46,330 of planetary gravity so kind of a 364 00:20:50,530 --> 00:20:48,770 partial influence here it should be 365 00:20:52,890 --> 00:20:50,540 tuned this to work on the earth that 366 00:20:57,370 --> 00:20:52,900 won't work on planets that are smaller 367 00:20:59,050 --> 00:20:57,380 or larger the other point in here is 368 00:21:01,210 --> 00:20:59,060 that we know what the thermal expansion 369 00:21:03,940 --> 00:21:01,220 coefficient is we know what the 370 00:21:06,930 --> 00:21:03,950 temperature contrast is we end up with a 371 00:21:12,430 --> 00:21:06,940 very small coefficient of friction of 372 00:21:14,650 --> 00:21:12,440 around for 100s which is too low to be 373 00:21:17,440 --> 00:21:14,660 for any reasonable material which means 374 00:21:26,560 --> 00:21:17,450 that we either need a dynamic weakening 375 00:21:28,780 --> 00:21:26,570 mechanism or we need to have a very high 376 00:21:31,660 --> 00:21:28,790 good pressure probably from subducted 377 00:21:34,090 --> 00:21:31,670 settlements so again something that we 378 00:21:35,360 --> 00:21:34,100 don't know a lot about the earth we know 379 00:21:38,330 --> 00:21:35,370 the subduction zone 380 00:21:40,610 --> 00:21:38,340 week on the earth but we don't you know 381 00:21:44,590 --> 00:21:40,620 kind of qualitatively why but certainly 382 00:21:47,390 --> 00:21:44,600 not quantitative clock ok the second out 383 00:21:54,430 --> 00:21:47,400 process I'm going to consider is the 384 00:21:57,710 --> 00:21:54,440 slab moving to viscous model if we solve 385 00:22:00,680 --> 00:21:57,720 the force balance equation between the 386 00:22:02,990 --> 00:22:00,690 slab and the resistance of the slab we 387 00:22:05,900 --> 00:22:03,000 get back the classical parametrize 388 00:22:09,050 --> 00:22:05,910 convection result the same one will 389 00:22:11,030 --> 00:22:09,060 apply to an ice of viscous fluid applies 390 00:22:14,300 --> 00:22:11,040 in this tape because the lithosphere is 391 00:22:15,590 --> 00:22:14,310 basically by assumption going on for a 392 00:22:18,350 --> 00:22:15,600 ride 393 00:22:25,190 --> 00:22:18,360 we get a very big slab it's going to be 394 00:22:26,960 --> 00:22:25,200 able possibly to overcome forces in the 395 00:22:29,540 --> 00:22:26,970 lithosphere like the friction and 396 00:22:32,720 --> 00:22:29,550 bending and all we have to consider is 397 00:22:35,410 --> 00:22:32,730 the fact that the slab can sink we see 398 00:22:39,560 --> 00:22:35,420 that we get gravity to the 1/3 power 399 00:22:44,050 --> 00:22:39,570 here we need heat flow proportional to 400 00:22:46,610 --> 00:22:44,060 gravity to balance radioactivity the 401 00:22:50,570 --> 00:22:46,620 parameters here we can change or the 402 00:22:53,420 --> 00:22:50,580 temperature contrasts at the surface and 403 00:22:55,820 --> 00:22:53,430 the viscosity we increase the 404 00:22:59,740 --> 00:22:55,830 temperature and interior it decreases 405 00:23:03,020 --> 00:22:59,750 viscosity increases this so we need 406 00:23:05,630 --> 00:23:03,030 balance radioactivity with heat form the 407 00:23:08,930 --> 00:23:05,640 silver we need to have a hotter than the 408 00:23:10,730 --> 00:23:08,940 earth on site we get relatively robust 409 00:23:14,090 --> 00:23:10,740 result this is the blunt see at all 410 00:23:18,380 --> 00:23:14,100 result you have a big slab on a small 411 00:23:21,440 --> 00:23:18,390 planet we the tactic here and just show 412 00:23:24,260 --> 00:23:21,450 it here an outline is that the slab 413 00:23:27,020 --> 00:23:24,270 sinks the drives fall and the fall of 414 00:23:29,390 --> 00:23:27,030 the lithosphere is going on for the ride 415 00:23:31,010 --> 00:23:29,400 it's all fascitis producing the only 416 00:23:34,070 --> 00:23:31,020 driving force will put the plate in 417 00:23:36,770 --> 00:23:34,080 tension we get a big enough slab it's 418 00:23:40,250 --> 00:23:36,780 going to overcome any forces in the 419 00:23:43,250 --> 00:23:40,260 lithosphere and the metal is going to be 420 00:23:46,490 --> 00:23:43,260 the dominant balance and we're back to 421 00:23:56,390 --> 00:23:46,500 the simple classical parameter ice 422 00:23:58,370 --> 00:23:56,400 so okay the again just to reiterate we 423 00:24:00,470 --> 00:23:58,380 can strive the equation either from 424 00:24:04,610 --> 00:24:00,480 force balance or work balance like 425 00:24:07,159 --> 00:24:04,620 villain see it all does the work on the 426 00:24:09,620 --> 00:24:07,169 megathrust and the bending of the slab 427 00:24:14,210 --> 00:24:09,630 becomes negligible if we have a big 428 00:24:16,399 --> 00:24:14,220 enough slab plates become likely there's 429 00:24:19,909 --> 00:24:16,409 a physical problem with this is that the 430 00:24:23,630 --> 00:24:19,919 viscosity increases without that the 431 00:24:26,690 --> 00:24:23,640 slab may do mainly work deforming the 432 00:24:30,289 --> 00:24:26,700 deep model and not have much work left 433 00:24:32,360 --> 00:24:30,299 over to be transmitted to the slab that 434 00:24:35,390 --> 00:24:32,370 the viscosity immediately under though 435 00:24:39,049 --> 00:24:35,400 if this fear may be quite well the slab 436 00:24:41,870 --> 00:24:39,059 will drive the wall but the it'll 437 00:24:44,090 --> 00:24:41,880 basically be effectively like ball 438 00:24:46,250 --> 00:24:44,100 bearings between the model and Miletus 439 00:24:47,180 --> 00:24:46,260 fare and the slab may not be able to put 440 00:24:52,460 --> 00:24:47,190 the lithosphere 441 00:24:56,680 --> 00:24:52,470 under compression a second problem here 442 00:24:58,399 --> 00:24:56,690 is if we do a parameterised convention 443 00:25:01,279 --> 00:24:58,409 calculation for the earth and 444 00:25:05,510 --> 00:25:01,289 extrapolate back in time we get into 445 00:25:11,299 --> 00:25:05,520 royal trouble the current a most 446 00:25:13,190 --> 00:25:11,309 accepted geochemical estimate for the 447 00:25:18,080 --> 00:25:13,200 radioactivity in the earth would produce 448 00:25:20,630 --> 00:25:18,090 a web land heat for a 24 noah watts per 449 00:25:23,149 --> 00:25:20,640 meter square the model on the east fall 450 00:25:25,370 --> 00:25:23,159 is seventy milliwatts per meter squared 451 00:25:30,260 --> 00:25:25,380 so if we believe this the earth is 452 00:25:34,310 --> 00:25:30,270 pulling like 180 or over a hundred 453 00:25:38,060 --> 00:25:34,320 degrees 100 K per billion years if we 454 00:25:40,669 --> 00:25:38,070 try to extrapolate back in time we 455 00:25:42,590 --> 00:25:40,679 extrapolate it back in time the metals 456 00:25:45,649 --> 00:25:42,600 hotter we have even more vigorous 457 00:25:48,260 --> 00:25:45,659 Convention and we strap away we get back 458 00:25:52,250 --> 00:25:48,270 even a billion years and we have the 459 00:25:54,529 --> 00:25:52,260 whole inside of the planet molten we 460 00:25:57,840 --> 00:25:54,539 know we have basically tectonics like 461 00:26:00,570 --> 00:25:57,850 the present at the time 462 00:26:03,750 --> 00:26:00,580 we have to crank up the heat while over 463 00:26:06,600 --> 00:26:03,760 double the box silicate earth like that 464 00:26:10,050 --> 00:26:06,610 before we get an acceptable thermal 465 00:26:12,360 --> 00:26:10,060 history or the planet starts out how to 466 00:26:15,600 --> 00:26:12,370 what we know it's H to be a really 2h 467 00:26:18,450 --> 00:26:15,610 after the month in pipe so we got two 468 00:26:21,660 --> 00:26:18,460 things here two assumptions that sound 469 00:26:24,240 --> 00:26:21,670 very good that the Madol controls the 470 00:26:28,800 --> 00:26:24,250 rate of plate tectonics and we have this 471 00:26:30,990 --> 00:26:28,810 good estimate how they constraints from 472 00:26:33,390 --> 00:26:31,000 plasma chemistry humming constraints 473 00:26:35,940 --> 00:26:33,400 from all we can sample from the interior 474 00:26:39,630 --> 00:26:35,950 of the earth Falls cannot be right at 475 00:26:43,710 --> 00:26:39,640 the time we either have to have the 476 00:26:48,900 --> 00:26:43,720 radioactivity estimate wall by over a 477 00:26:50,730 --> 00:26:48,910 factor of two will soon the neutrino 478 00:26:53,250 --> 00:26:50,740 detectors anti neutrinos from 479 00:26:55,980 --> 00:26:53,260 radioactive decay in the earth so we 480 00:26:59,100 --> 00:26:55,990 will know the absolute radioactive heat 481 00:27:01,380 --> 00:26:59,110 generation we will know the absolute 482 00:27:05,640 --> 00:27:01,390 abundance of uranium and thorium in the 483 00:27:09,180 --> 00:27:05,650 earth and we'll be able to check to see 484 00:27:11,610 --> 00:27:09,190 if what it's right 485 00:27:14,940 --> 00:27:11,620 the alternative is this elegant 486 00:27:17,520 --> 00:27:14,950 assumption that the model if big we have 487 00:27:20,100 --> 00:27:17,530 big slabs sinking into a huge metal is 488 00:27:23,550 --> 00:27:20,110 wrong and that the plates really control 489 00:27:27,000 --> 00:27:23,560 the rate on your earth if that is the 490 00:27:30,060 --> 00:27:27,010 case the the assumption that Allen 491 00:27:35,930 --> 00:27:30,070 Arctic made could possibly destructive 492 00:27:41,940 --> 00:27:35,940 original control our we have the ultra 493 00:27:45,780 --> 00:27:41,950 tip here that we have control by the 494 00:27:49,170 --> 00:27:45,790 bending and a yield stress okay 495 00:27:53,520 --> 00:27:49,180 the ridge push force its relative given 496 00:27:56,220 --> 00:27:53,530 it already relatively easy to derive we 497 00:27:59,930 --> 00:27:56,230 cannot have the vertical pressure and a 498 00:28:04,140 --> 00:27:59,940 floating object and a surrounding fluid 499 00:28:08,880 --> 00:28:04,150 equal to the horizontal stress in in 500 00:28:10,520 --> 00:28:08,890 both viewing this in terms of work if we 501 00:28:13,430 --> 00:28:10,530 have 502 00:28:15,590 --> 00:28:13,440 if we had the solid here that was 503 00:28:19,580 --> 00:28:15,600 buoyant it would spread out like oil 504 00:28:22,820 --> 00:28:19,590 over wine in the case of the earth the 505 00:28:27,800 --> 00:28:22,830 ridges weeks are have a buoyant weak 506 00:28:30,050 --> 00:28:27,810 foot and we have a strong dense 507 00:28:33,560 --> 00:28:30,060 lithosphere so the lithosphere will be 508 00:28:36,050 --> 00:28:33,570 put into compression mathematically the 509 00:28:39,290 --> 00:28:36,060 stress resolving to stress times the 510 00:28:42,110 --> 00:28:39,300 thickness of the lithosphere is equal to 511 00:28:44,060 --> 00:28:42,120 this triangle that you formed by 512 00:28:47,480 --> 00:28:44,070 clotting the vertical stress in both 513 00:28:51,200 --> 00:28:47,490 objects the vertical and here is the 514 00:28:53,210 --> 00:28:51,210 elevation of our but the plates are in 515 00:28:55,790 --> 00:28:53,220 compression on the earth we know this 516 00:28:57,980 --> 00:28:55,800 from inner plate earthquakes so we have 517 00:29:01,670 --> 00:28:57,990 the possibility that this rich forst 518 00:29:04,040 --> 00:29:01,680 forst we want to go to europa we have 519 00:29:08,690 --> 00:29:04,050 our to the situation are drawn here to 520 00:29:12,380 --> 00:29:08,700 get a simpler analogy the thinnest ice 521 00:29:17,150 --> 00:29:12,390 on Europa is the weakest so we have a 522 00:29:20,570 --> 00:29:17,160 weak fluid against a strong boy and 523 00:29:23,030 --> 00:29:20,580 solid so the thick ice the high 524 00:29:33,230 --> 00:29:23,040 elevations in Europa will be in this 525 00:29:39,310 --> 00:29:33,240 membrane attention okay we can balance a 526 00:29:44,780 --> 00:29:39,320 yield stress against this Ridge push 527 00:29:48,860 --> 00:29:44,790 stress acting through the planet and in 528 00:29:53,960 --> 00:29:48,870 that case we get the thickness of the 529 00:29:56,630 --> 00:29:53,970 lithosphere scales to 1 over gravity the 530 00:29:59,390 --> 00:29:56,640 heat flow will scale to 1 over the let 531 00:30:01,820 --> 00:29:59,400 this old lithosphere thickness so in 532 00:30:05,480 --> 00:30:01,830 that case we get heat 12 scaling to 533 00:30:09,160 --> 00:30:05,490 gravity and that we have plate tectonics 534 00:30:12,880 --> 00:30:09,170 by this mechanism on the super earth 535 00:30:15,940 --> 00:30:12,890 where we get earth-like temperatures 536 00:30:19,880 --> 00:30:15,950 throughout its history and it basically 537 00:30:22,550 --> 00:30:19,890 behaves like the earth does where it has 538 00:30:24,710 --> 00:30:22,560 a lettuce pair of thinner thickness 539 00:30:27,680 --> 00:30:24,720 but the same pressure at the base of 540 00:30:31,340 --> 00:30:27,690 express everything in terms of pressure 541 00:30:33,830 --> 00:30:31,350 things work very simply for this the 542 00:30:41,380 --> 00:30:33,840 assumption here is that depending of a 543 00:30:48,050 --> 00:30:41,390 slab rather than the slip on vection 544 00:30:50,060 --> 00:30:48,060 okay back to the friction again we get 545 00:30:52,550 --> 00:30:50,070 the result in terms of material 546 00:30:55,250 --> 00:30:52,560 properties it doesn't and you can't say 547 00:30:58,790 --> 00:30:55,260 anything from that about the 548 00:31:01,910 --> 00:30:58,800 relationship to size but it went to 549 00:31:05,120 --> 00:31:01,920 model I can on the owner anodic one will 550 00:31:08,480 --> 00:31:05,130 just give fake tectonics on an object on 551 00:31:10,610 --> 00:31:08,490 a large object and earth size option 552 00:31:15,770 --> 00:31:10,620 cannot give plate tectonics on a big one 553 00:31:18,110 --> 00:31:15,780 or smaller and this is again the matura 554 00:31:20,690 --> 00:31:18,120 property again reminding us that we need 555 00:31:23,990 --> 00:31:20,700 a very low stress but your coefficient 556 00:31:26,720 --> 00:31:24,000 of friction we don't really understand 557 00:31:28,660 --> 00:31:26,730 why the coefficient of friction is low 558 00:31:33,070 --> 00:31:28,670 on the earth we understand qualitatively 559 00:31:37,610 --> 00:31:33,080 but certainly not quantitatively okay 560 00:31:40,750 --> 00:31:37,620 we've gone through I basically the 561 00:31:43,370 --> 00:31:40,760 Valencia doll model is matter wide 562 00:31:46,790 --> 00:31:43,380 driven flow by the effectively by the 563 00:31:49,580 --> 00:31:46,800 slab the O'Neill and Lonard ik is 564 00:31:54,650 --> 00:31:49,590 friction and balancing rich push force 565 00:31:59,540 --> 00:31:54,660 and we could see where we come from but 566 00:32:05,980 --> 00:31:59,550 we can't really extrapolate okay let's 567 00:32:09,860 --> 00:32:05,990 see about geochemical cycles we can have 568 00:32:11,990 --> 00:32:09,870 plates works nice on the earth if we're 569 00:32:15,590 --> 00:32:12,000 lucky enough to get plates things work 570 00:32:18,920 --> 00:32:15,600 fine if we have a volcanic planet we get 571 00:32:21,560 --> 00:32:18,930 very vigorous geochemical cycles we have 572 00:32:25,130 --> 00:32:21,570 very reactive material erupting to the 573 00:32:28,670 --> 00:32:25,140 surface we get Hydra straighted 574 00:32:30,650 --> 00:32:28,680 carbonated material melting at depth we 575 00:32:32,300 --> 00:32:30,660 get something that kinda looks like the 576 00:32:34,430 --> 00:32:32,310 earth and pot scientists have claimed 577 00:32:35,750 --> 00:32:34,440 the Archaean of the Earth may have 578 00:32:38,540 --> 00:32:35,760 behaved this way 579 00:32:40,490 --> 00:32:38,550 rather than strictly having plates if we 580 00:32:42,500 --> 00:32:40,500 have a stagnant lid prior that we can 581 00:32:45,650 --> 00:32:42,510 get that in two ways the thickness of 582 00:32:48,290 --> 00:32:45,660 continental crust is such that a cup 583 00:32:50,090 --> 00:32:48,300 volume of it you know big planets where 584 00:32:52,840 --> 00:32:50,100 raw material to make crust covers the 585 00:32:56,950 --> 00:32:52,850 whole planet or we can get in this 586 00:32:59,330 --> 00:32:56,960 friction dominated machine where we get 587 00:33:01,610 --> 00:32:59,340 something that may have some plate 588 00:33:04,490 --> 00:33:01,620 tectonics but it's sluggish can't 589 00:33:08,720 --> 00:33:04,500 transport the heat so we have a hot 590 00:33:11,630 --> 00:33:08,730 material the stagnant lid heat flow 591 00:33:14,210 --> 00:33:11,640 works okay because for it to get 592 00:33:18,290 --> 00:33:14,220 operated it works like the parameter ice 593 00:33:19,970 --> 00:33:18,300 convection result that I had before we 594 00:33:23,780 --> 00:33:19,980 have to have the interior of the planet 595 00:33:26,840 --> 00:33:23,790 quite hot to get the heat out of a super 596 00:33:31,010 --> 00:33:26,850 earth or even an earth-sized planet so 597 00:33:33,560 --> 00:33:31,020 we still get vulcanism we get a like ma 598 00:33:37,220 --> 00:33:33,570 maybe ma hot spot organism or I'll 599 00:33:38,840 --> 00:33:37,230 Balkan ism but we still have volcanism 600 00:33:41,840 --> 00:33:38,850 we still get a perfectly good 601 00:33:44,690 --> 00:33:41,850 geochemical cycle effect the details 602 00:33:52,670 --> 00:33:44,700 about the gift but not affect what we 603 00:33:56,030 --> 00:33:52,680 get overall okay if we use a oh it's not 604 00:33:59,570 --> 00:33:56,040 a direct analog because gravity is not 605 00:34:02,060 --> 00:33:59,580 important there and actually behavior 606 00:34:04,040 --> 00:34:02,070 closer to stagnant letters I've driven 607 00:34:07,910 --> 00:34:04,050 convection will work for our large 608 00:34:10,280 --> 00:34:07,920 planet that the inside of the planet 609 00:34:12,940 --> 00:34:10,290 must fall because the inside is not 610 00:34:15,710 --> 00:34:12,950 going to be malt on the deep inside 611 00:34:20,210 --> 00:34:15,720 planet with large gravity large pressure 612 00:34:21,830 --> 00:34:20,220 at depth and will basically get 613 00:34:25,970 --> 00:34:21,840 convection where the rate of the 614 00:34:28,369 --> 00:34:25,980 convection staying that led our front of 615 00:34:30,800 --> 00:34:28,379 our classic parameterised convection 616 00:34:33,110 --> 00:34:30,810 formula will give close to the right 617 00:34:35,899 --> 00:34:33,120 result the vulcanism gets the heat out 618 00:34:38,000 --> 00:34:35,909 the last little bit to the left is fair 619 00:34:41,690 --> 00:34:38,010 but it's not the rate limiting stuff 620 00:34:43,490 --> 00:34:41,700 like it is ideal where the gravity 621 00:34:46,909 --> 00:34:43,500 causes the pressure to just slightly 622 00:34:48,780 --> 00:34:46,919 increase with depth we could totally Mel 623 00:34:50,580 --> 00:34:48,790 the silicate planet 624 00:34:53,100 --> 00:34:50,590 they'd get material where they get 625 00:34:57,440 --> 00:34:53,110 ultramafic material like olivine will 626 00:35:00,750 --> 00:34:57,450 give them alcohol and ocean or we could 627 00:35:03,990 --> 00:35:00,760 remail tigris material and get more 628 00:35:06,720 --> 00:35:04,000 granitic Magnus we could end up with the 629 00:35:10,710 --> 00:35:06,730 crust of the planet melting at its base 630 00:35:14,370 --> 00:35:10,720 and just simply that acting is a heat 631 00:35:16,860 --> 00:35:14,380 transfer mechanism we know that this has 632 00:35:22,290 --> 00:35:16,870 not happened in the last 3.8 billion 633 00:35:24,930 --> 00:35:22,300 years probably the last 4.2 or 4.3 where 634 00:35:27,420 --> 00:35:24,940 the interior huh was hot enough that 635 00:35:30,890 --> 00:35:27,430 we've had continuous melting everywhere 636 00:35:34,650 --> 00:35:30,900 at the base of the continental crust we 637 00:35:38,070 --> 00:35:34,660 know that simply because where we start 638 00:35:40,290 --> 00:35:38,080 to see rocks of 3/8 we're not getting 639 00:35:43,230 --> 00:35:40,300 continuous volcanic scumming out of the 640 00:35:45,960 --> 00:35:43,240 interior rather receive our regular 641 00:35:48,690 --> 00:35:45,970 sedimentary rocks and there's irk on 642 00:35:51,570 --> 00:35:48,700 sweets we see peeks of activity and peak 643 00:35:53,310 --> 00:35:51,580 supply elsens in the ancient sir con 644 00:35:55,380 --> 00:35:53,320 seats just like we do now they're a 645 00:35:56,720 --> 00:35:55,390 little bit peeps are a bit closer 646 00:35:59,280 --> 00:35:56,730 together 647 00:36:01,370 --> 00:35:59,290 we couldn't observe peaks that were a 648 00:36:05,430 --> 00:36:01,380 billion years of hardware we only have 649 00:36:08,730 --> 00:36:05,440 500 million years of record but we still 650 00:36:12,210 --> 00:36:08,740 have periods of high essence and periods 651 00:36:17,670 --> 00:36:12,220 of activity rather than continuous 652 00:36:20,580 --> 00:36:17,680 melting at the base of the crust the 653 00:36:23,760 --> 00:36:20,590 statement that vulcanism again we have 654 00:36:26,040 --> 00:36:23,770 just a small layer that's not that has 655 00:36:29,130 --> 00:36:26,050 viscosity like the interior actually 656 00:36:33,870 --> 00:36:29,140 conducting leads to the interior being 657 00:36:35,970 --> 00:36:33,880 hotness of already mentioned okay we can 658 00:36:40,470 --> 00:36:35,980 compute ocean depth we make the 659 00:36:42,960 --> 00:36:40,480 assumption that most of the water in the 660 00:36:47,100 --> 00:36:42,970 planet Early's much of it ends up in the 661 00:36:52,020 --> 00:36:47,110 ocean on the earth one of the paradigms 662 00:36:55,530 --> 00:36:52,030 is that the earth model can only take so 663 00:36:57,810 --> 00:36:55,540 much water the subduction zone tries to 664 00:37:00,120 --> 00:36:57,820 spend down too much water we get melting 665 00:37:02,370 --> 00:37:00,130 at the island arc the island are 666 00:37:06,180 --> 00:37:02,380 volcanic comes up we get an eruption 667 00:37:08,850 --> 00:37:06,190 like mount st. Helen and the water is 668 00:37:10,980 --> 00:37:08,860 back at the surface this is that we have 669 00:37:13,860 --> 00:37:10,990 something like a coal trap and an old 670 00:37:16,170 --> 00:37:13,870 refrigerator this is a water trap that 671 00:37:17,280 --> 00:37:16,180 the whole model has to eventually pass 672 00:37:20,310 --> 00:37:17,290 through the regex 673 00:37:24,180 --> 00:37:20,320 subduction zone so we have a sluggish 674 00:37:27,510 --> 00:37:24,190 system but that the water gets back out 675 00:37:30,950 --> 00:37:27,520 at the subduction zone there various 676 00:37:33,450 --> 00:37:30,960 things that are basically we pipe 677 00:37:36,780 --> 00:37:33,460 reasoning that claim that you can get 678 00:37:39,780 --> 00:37:36,790 much more water in the model but this is 679 00:37:42,600 --> 00:37:39,790 basically the oniy hypothesis that 680 00:37:45,960 --> 00:37:42,610 really fully includes plate tectonics 681 00:37:48,420 --> 00:37:45,970 that may not necessarily be correct but 682 00:37:51,780 --> 00:37:48,430 it leaves there with a little bit of 683 00:37:54,680 --> 00:37:51,790 geometry the ocean depth scales with 684 00:37:57,990 --> 00:37:54,690 gravity the height of the topography 685 00:38:02,160 --> 00:37:58,000 again using the scaling relationships of 686 00:38:06,780 --> 00:38:02,170 driving force from the buoyancy of the 687 00:38:09,830 --> 00:38:06,790 ridge scales inversely with gravity and 688 00:38:14,970 --> 00:38:09,840 we have a small ocean it will protect I 689 00:38:18,630 --> 00:38:14,980 guess a small asteroid get up a big 690 00:38:20,730 --> 00:38:18,640 enough asteroid gets to vaporize the 691 00:38:23,280 --> 00:38:20,740 ocean it takes forever for it to rain 692 00:38:25,530 --> 00:38:23,290 out at the greenhouse special and we 693 00:38:29,810 --> 00:38:25,540 sterilized any subsurface from the 694 00:38:33,120 --> 00:38:29,820 residual there's no subsurface residual 695 00:38:36,360 --> 00:38:33,130 the ocean crust is thin that the water 696 00:38:40,980 --> 00:38:36,370 is deep these kind of cancel each other 697 00:38:43,860 --> 00:38:40,990 out big asteroid impact moderately big 698 00:38:46,110 --> 00:38:43,870 when they actually assume nate'll if we 699 00:38:48,840 --> 00:38:46,120 had a dry super earth where the ocean 700 00:38:53,070 --> 00:38:48,850 crust is thin then it would be easy to 701 00:38:55,950 --> 00:38:53,080 assume that we end up with lots of 702 00:39:00,740 --> 00:38:55,960 material tricks and Carnot's this is 703 00:39:03,360 --> 00:39:00,750 just Gauss's law for water we have the 704 00:39:05,430 --> 00:39:03,370 area of the planet scared the thickness 705 00:39:07,680 --> 00:39:05,440 of the ocean the density of the water is 706 00:39:09,930 --> 00:39:07,690 equal to the concentration of water in 707 00:39:12,810 --> 00:39:09,940 the planet times the mass of the planet 708 00:39:15,530 --> 00:39:12,820 and we solve for this and we get a 709 00:39:17,690 --> 00:39:15,540 proportionality to gravity 710 00:39:20,930 --> 00:39:17,700 firstly proportional to the density of 711 00:39:22,700 --> 00:39:20,940 water which is the material property we 712 00:39:25,180 --> 00:39:22,710 don't really know what the concentration 713 00:39:27,410 --> 00:39:25,190 of the water is and super-earth if 714 00:39:29,330 --> 00:39:27,420 anything it's going to be easier to 715 00:39:32,780 --> 00:39:29,340 accrete by a pulse on a big object 716 00:39:34,460 --> 00:39:32,790 rather than small on too much volatile 717 00:39:39,770 --> 00:39:34,470 gives us nothing tunes so there's going 718 00:39:43,610 --> 00:39:39,780 to be a limit to this but if we just 719 00:39:46,310 --> 00:39:43,620 take this a first order we're likely to 720 00:39:49,460 --> 00:39:46,320 end up with Waterworld on super earth 721 00:39:51,680 --> 00:39:49,470 where I'd be we have water or a world 722 00:39:54,050 --> 00:39:51,690 Europa in our own solar system we don't 723 00:39:56,810 --> 00:39:54,060 have an earth-sized Waterworld but 724 00:39:59,150 --> 00:39:56,820 considering a water world it's worth 725 00:40:01,940 --> 00:39:59,160 doing even if we don't find a super 726 00:40:06,700 --> 00:40:01,950 earth one because we made well find an 727 00:40:09,530 --> 00:40:06,710 earth-like one elsewhere okay we have 728 00:40:12,710 --> 00:40:09,540 processes of scale to gravitational 729 00:40:15,890 --> 00:40:12,720 potential and why the processes on a 730 00:40:19,190 --> 00:40:15,900 super earth is going to be very hard for 731 00:40:22,250 --> 00:40:19,200 hydrogen to get out and we may end up 732 00:40:25,160 --> 00:40:22,260 with a hydrogen-rich atmosphere rather 733 00:40:29,420 --> 00:40:25,170 than an strongly reducing atmosphere 734 00:40:34,940 --> 00:40:29,430 where co2 is a trace constituent rather 735 00:40:37,760 --> 00:40:34,950 than a fondant one the direct effects of 736 00:40:40,850 --> 00:40:37,770 a super-earth are dead 737 00:40:44,840 --> 00:40:40,860 barring microbes are really not affected 738 00:40:46,610 --> 00:40:44,850 directly by gravity large organisms if 739 00:40:50,270 --> 00:40:46,620 you've read any science fiction book 740 00:40:52,820 --> 00:40:50,280 football to where they add water 741 00:40:55,880 --> 00:40:52,830 organisms if they're large or neutrally 742 00:40:57,650 --> 00:40:55,890 buoyant and you go get start organizing 743 00:40:59,750 --> 00:40:57,660 some land 744 00:41:03,650 --> 00:40:59,760 the interesting thing here is the 745 00:41:07,490 --> 00:41:03,660 reducing atmosphere sediments dominated 746 00:41:12,760 --> 00:41:07,500 by carbon organic carbon rather than by 747 00:41:16,990 --> 00:41:12,770 carbonates and we're also going to have 748 00:41:20,150 --> 00:41:17,000 niches we can't have both lots of hot 749 00:41:23,810 --> 00:41:20,160 hydrogen and lots of co2 together on a 750 00:41:25,220 --> 00:41:23,820 common planet while the first life forms 751 00:41:27,410 --> 00:41:25,230 to evolve on the earth 752 00:41:31,910 --> 00:41:27,420 managin so they're relatively easily 753 00:41:36,560 --> 00:41:31,920 evolved and they will react hydrogen 754 00:41:40,040 --> 00:41:36,570 with co2 if we have a reducing planet 755 00:41:44,290 --> 00:41:40,050 where hydrogen is dominant co2 will 756 00:41:47,540 --> 00:41:44,300 become the light the limiting after 757 00:41:51,140 --> 00:41:47,550 photosynthesis would help you put in Sun 758 00:41:55,220 --> 00:41:51,150 energy to help grab the co2 but you're 759 00:41:57,680 --> 00:41:55,230 still have problems there are other 760 00:42:02,300 --> 00:41:57,690 Nicias here these are highly speculative 761 00:42:07,130 --> 00:42:02,310 a shopping list various ways here to you 762 00:42:08,840 --> 00:42:07,140 methane and water as a substrate to make 763 00:42:13,359 --> 00:42:08,850 organic matter with different 764 00:42:16,310 --> 00:42:13,369 intermediate steps monoxide is a poison 765 00:42:19,849 --> 00:42:16,320 icing Li it's very good high energy 766 00:42:25,430 --> 00:42:19,859 source very good for microbes that could 767 00:42:31,730 --> 00:42:25,440 make out of that we can make hydrogen an 768 00:42:34,490 --> 00:42:31,740 organic matter we can use co2 which is 769 00:42:39,800 --> 00:42:34,500 in short supply or carbon monoxide for 770 00:42:42,440 --> 00:42:39,810 intermediate steps we don't have 771 00:42:46,790 --> 00:42:42,450 organisms that do methane photosynthesis 772 00:42:50,210 --> 00:42:46,800 at least known on the earth but so it is 773 00:42:52,550 --> 00:42:50,220 a speculation the intermediate steps 774 00:42:58,170 --> 00:42:52,560 that got that part are no longer 775 00:43:08,740 --> 00:43:01,180 what other choices we can star an 776 00:43:16,860 --> 00:43:08,750 oxidant dumb choice is o2 that oxygen 777 00:43:27,310 --> 00:43:22,480 making oxidants by gathering light we 778 00:43:30,400 --> 00:43:27,320 have organisms that do photosynthesis 779 00:43:33,730 --> 00:43:30,410 using FeO we have organisms that do 780 00:43:35,950 --> 00:43:33,740 photosynthesis doing sulfides we have 781 00:43:39,100 --> 00:43:35,960 none that I know of that directly makes 782 00:43:44,470 --> 00:43:39,110 hydrogen and store the oxygen for later 783 00:43:46,570 --> 00:43:44,480 use now we can get exotic manganese is 784 00:43:50,980 --> 00:43:46,580 hopefully involved in photosynthesis on 785 00:43:53,250 --> 00:43:50,990 the earth there's apparently no organism 786 00:43:57,790 --> 00:43:53,260 that makes a manganate or permanganate 787 00:44:01,210 --> 00:43:57,800 in photosynthesis there argan isn't that 788 00:44:05,350 --> 00:44:01,220 make nitrate from Mike right and 789 00:44:08,590 --> 00:44:05,360 photosynthesis we could make nitrates 790 00:44:10,840 --> 00:44:08,600 easy to star we could even star the 791 00:44:13,350 --> 00:44:10,850 organic matter and the nitrate together 792 00:44:17,230 --> 00:44:13,360 make something like night for cellulose 793 00:44:20,760 --> 00:44:17,240 nothing does that on the earth we can 794 00:44:25,300 --> 00:44:20,770 make calcium or manganese magnesium 795 00:44:27,880 --> 00:44:25,310 peroxide these are can be solid so to 796 00:44:32,400 --> 00:44:27,890 saturate the solution for the calcium 797 00:44:36,430 --> 00:44:32,410 one easy to star it's used on the earth 798 00:44:39,310 --> 00:44:36,440 it's not peroxides are heavily involved 799 00:44:42,070 --> 00:44:39,320 in biochemistry on the earth organisms 800 00:44:44,530 --> 00:44:42,080 can make and destroy them they don't use 801 00:44:47,320 --> 00:44:44,540 them as an energy resource as far as you 802 00:44:51,640 --> 00:44:47,330 know nothing gets its ATP as far as 803 00:44:55,120 --> 00:44:51,650 known out of oxide calcium peroxide is 804 00:44:57,700 --> 00:44:55,130 stable it has industrial uses like 805 00:45:00,700 --> 00:44:57,710 cleaning are like putting a rock on 806 00:45:02,350 --> 00:45:00,710 right seats and rice paddies so the 807 00:45:07,099 --> 00:45:02,360 environment around the right seed 808 00:45:13,679 --> 00:45:10,349 animals if we're going to get animals on 809 00:45:19,679 --> 00:45:13,689 our super earth if we like Ichi to call 810 00:45:22,769 --> 00:45:19,689 home planet did not lose lots of 811 00:45:25,679 --> 00:45:22,779 hydrogen escape when it was quite hot 812 00:45:30,839 --> 00:45:25,689 and accreting we may end up with a 813 00:45:35,459 --> 00:45:30,849 reducing metal the Earth's model is much 814 00:45:39,959 --> 00:45:35,469 more oxidized than the model Mars it 815 00:45:43,140 --> 00:45:39,969 slightly oxidized the movement which is 816 00:45:46,439 --> 00:45:43,150 reduced enough that it's close to 817 00:45:48,929 --> 00:45:46,449 equilibrium with iron nickel metal the 818 00:45:52,109 --> 00:45:48,939 model of death is also reduced so if we 819 00:45:55,049 --> 00:45:52,119 can't get hydrogen out during the 820 00:45:57,029 --> 00:45:55,059 accreting the model may stay reduced at 821 00:46:01,410 --> 00:45:57,039 high temperatures will still probably 822 00:46:04,259 --> 00:46:01,420 get slight amount co2 coming out of 823 00:46:07,679 --> 00:46:04,269 volcanoes just simply because you 824 00:46:09,829 --> 00:46:07,689 partition into all the easily produce 825 00:46:13,979 --> 00:46:09,839 species at a high enough temperature 826 00:46:18,900 --> 00:46:13,989 it's not a tempted to calculate any of 827 00:46:23,009 --> 00:46:18,910 these okay we have a question from Penn 828 00:46:28,019 --> 00:46:23,019 State I know I'm the chimp casting can 829 00:46:30,029 --> 00:46:28,029 you hear me out and Claire yeah so 830 00:46:31,979 --> 00:46:30,039 you're you conclude that these super 831 00:46:35,160 --> 00:46:31,989 Earths will have reduced atmospheres 832 00:46:37,079 --> 00:46:35,170 with lots of methane you know that's 833 00:46:38,910 --> 00:46:37,089 true on giant planets but those 834 00:46:41,759 --> 00:46:38,920 atmospheres are infinitely deep 835 00:46:44,609 --> 00:46:41,769 essentially so that methane is reformed 836 00:46:46,380 --> 00:46:44,619 at depth these atmospheres of theory if 837 00:46:48,299 --> 00:46:46,390 the planets are habitable are not that 838 00:46:50,999 --> 00:46:48,309 deep it's not that easy to make methane 839 00:46:53,279 --> 00:46:51,009 in the atmosphere but it is easy to 840 00:47:04,349 --> 00:46:53,289 destroy it photochemically I mean what's 841 00:47:08,579 --> 00:47:04,359 the source for the methane a biotic Lea 842 00:47:10,949 --> 00:47:08,589 their other source the methane would be 843 00:47:14,069 --> 00:47:10,959 that we have very vigorous tectonics of 844 00:47:17,910 --> 00:47:14,079 any of the methane haze Falls to the 845 00:47:19,020 --> 00:47:17,920 surface the materials very soon if it's 846 00:47:23,790 --> 00:47:19,030 not Eden is going 847 00:47:28,290 --> 00:47:23,800 gets abducted worse abducting material 848 00:47:30,680 --> 00:47:28,300 into a presumably hydrous model so we 849 00:47:36,710 --> 00:47:30,690 should get some methane back at the heat 850 00:47:41,790 --> 00:47:39,270 approximation look at it kinetically 851 00:47:44,940 --> 00:47:41,800 because you know if you've got hydrogen 852 00:47:47,240 --> 00:47:44,950 escaping to space probably coming from 853 00:47:50,370 --> 00:47:47,250 water that gives you a source of oxygen 854 00:47:53,220 --> 00:47:50,380 not pre oxygen but enough oxygen to 855 00:47:54,960 --> 00:47:53,230 oxidize some of that methane to co2 so 856 00:47:57,270 --> 00:47:54,970 I'm not that convinced it would be that 857 00:47:59,940 --> 00:47:57,280 different from the early Earth the a 858 00:48:03,780 --> 00:47:59,950 body I agree with your scenario 859 00:48:07,290 --> 00:48:03,790 completely for the earth there's going 860 00:48:10,080 --> 00:48:07,300 to be a significantly high gravitational 861 00:48:12,420 --> 00:48:10,090 potential where it becomes difficult for 862 00:48:15,870 --> 00:48:12,430 hydrogen to get out I there's 863 00:48:19,640 --> 00:48:15,880 disagreement like with the between Dave 864 00:48:23,310 --> 00:48:19,650 cowling that and with the TMO all paper 865 00:48:26,910 --> 00:48:23,320 on whether the efficacy of hydrogen 866 00:48:30,390 --> 00:48:26,920 escape even from the earth 867 00:48:34,140 --> 00:48:30,400 so I basically taken an agnostic 868 00:48:38,760 --> 00:48:34,150 position there but recognized that we 869 00:48:41,270 --> 00:48:38,770 may get a reducing planet so we need to 870 00:48:43,650 --> 00:48:41,280 think about it and I agree kinetics 871 00:48:47,520 --> 00:48:43,660 considering what really happens in the 872 00:48:49,770 --> 00:48:47,530 atmosphere and then throwing relatively 873 00:48:52,830 --> 00:48:49,780 simple life forms into it it's the right 874 00:48:55,680 --> 00:48:52,840 wait involved I just did the simplest 875 00:48:58,650 --> 00:48:55,690 gases I could think of that would farm 876 00:49:01,320 --> 00:48:58,660 if we had a reducing atmosphere okay I 877 00:49:03,180 --> 00:49:01,330 agree I've got fun Ken visiting this 878 00:49:10,250 --> 00:49:03,190 week so fun we need to do that 879 00:49:16,980 --> 00:49:12,870 okay do we have any questions here in 880 00:49:23,650 --> 00:49:16,990 nai central we have a room fo Kevin's on 881 00:49:25,720 --> 00:49:23,660 Lake the largest planet 882 00:49:27,670 --> 00:49:25,730 have more and I imagine that every 883 00:49:34,109 --> 00:49:27,680 parcel I bring to the surface from the 884 00:49:40,200 --> 00:49:37,870 was in my model right and so I have the 885 00:49:52,569 --> 00:49:40,210 surface to volume ratio would give me a 886 00:50:10,589 --> 00:49:52,579 larger amount of he'll spread out and 887 00:50:15,400 --> 00:50:13,420 couple things here the we don't know the 888 00:50:19,450 --> 00:50:15,410 efficacy which the continent will get 889 00:50:22,270 --> 00:50:19,460 lease abductive we have more material to 890 00:50:26,520 --> 00:50:22,280 make it if we end up in that case we'll 891 00:50:30,579 --> 00:50:26,530 end up with probably a continental 892 00:50:32,559 --> 00:50:30,589 vulcanism dominated planet with some 893 00:50:39,329 --> 00:50:32,569 basaltic volcanism that makes it up 894 00:50:41,500 --> 00:50:39,339 through we have-we eppley the planets 895 00:50:47,980 --> 00:50:41,510 well have the planet covered with 896 00:50:50,440 --> 00:50:47,990 volcanoes yes yes we will not get shale 897 00:50:52,870 --> 00:50:50,450 will not get Paul mountains if you want 898 00:50:56,230 --> 00:50:52,880 something like the Appalachians the 899 00:50:58,180 --> 00:50:56,240 aliens there will have to put out their 900 00:51:01,569 --> 00:50:58,190 low gravity suit and travel to the earth 901 00:51:06,700 --> 00:51:01,579 you will not have this you will not get 902 00:51:11,440 --> 00:51:06,710 the basic classes of sedimentary rocks 903 00:51:14,980 --> 00:51:11,450 we will not get organisms that evolved 904 00:51:18,760 --> 00:51:14,990 to do soil weathering will have some 905 00:51:20,950 --> 00:51:18,770 organisms that evolved to whether the 906 00:51:23,890 --> 00:51:20,960 whatever rock they find on the base of 907 00:51:28,299 --> 00:51:23,900 the ocean but will still have things 908 00:51:30,549 --> 00:51:28,309 recycle but we will get a little 909 00:51:33,430 --> 00:51:30,559 offending land we may end up with the 910 00:51:35,280 --> 00:51:33,440 continental crust getting from a DAT 911 00:51:38,310 --> 00:51:35,290 culkin ism can get through 912 00:51:41,490 --> 00:51:38,320 Bahria that may get swamped and gets 913 00:51:44,640 --> 00:51:41,500 abducted so they're both enemies for 914 00:51:50,490 --> 00:51:44,650 here but this line of continental crust 915 00:51:52,410 --> 00:51:50,500 and ocean as definitely a possibility a 916 00:51:57,390 --> 00:51:52,420 possibility that we'll have geochemical 917 00:52:00,090 --> 00:51:57,400 cycles but not plates we have a question 918 00:52:02,550 --> 00:52:00,100 from Jack Lutz our you made a 919 00:52:05,280 --> 00:52:02,560 super-earth from generally more 920 00:52:11,430 --> 00:52:05,290 refractory material so you have a 921 00:52:14,850 --> 00:52:11,440 reasonable amount of water what would be 922 00:52:16,710 --> 00:52:14,860 what would be like most of the current 923 00:52:20,370 --> 00:52:16,720 hiepro comes from the uranium and 924 00:52:23,460 --> 00:52:20,380 thorium so if you if you make it more 925 00:52:25,470 --> 00:52:23,470 refractory you'll get more of that you 926 00:52:28,550 --> 00:52:25,480 lose a little bit of potassium so the 927 00:52:32,130 --> 00:52:28,560 radioactivity will be just a bit hotter 928 00:52:35,850 --> 00:52:32,140 the radioactivity declines by a factor 929 00:52:38,910 --> 00:52:35,860 of a few over the Prentice age so I 930 00:52:47,760 --> 00:52:38,920 think I'll have a modest effect if we 931 00:52:50,970 --> 00:52:47,770 end up getting we very little material 932 00:52:54,180 --> 00:52:50,980 to make crust the part of the crust is 933 00:52:56,330 --> 00:52:54,190 aluminium and calcium which is silica 934 00:52:58,890 --> 00:52:56,340 which we have officer I have plenty up 935 00:53:00,960 --> 00:52:58,900 we'd end up with something that's more 936 00:53:02,990 --> 00:53:00,970 like a plaid your granite the granite 937 00:53:07,940 --> 00:53:03,000 formed at the mid-ocean ridge axis 938 00:53:14,880 --> 00:53:07,950 sodium granite than a classic granite 939 00:53:17,730 --> 00:53:14,890 again going to affect details the long 940 00:53:19,130 --> 00:53:17,740 as we have some trace potassium that 941 00:53:22,950 --> 00:53:19,140 will be available as a biological 942 00:53:25,380 --> 00:53:22,960 element that almost all the potassium of 943 00:53:28,370 --> 00:53:25,390 the earth even near the surface is not 944 00:53:35,340 --> 00:53:32,490 yeah the Amazon Arnulfo region with a 945 00:53:37,800 --> 00:53:35,350 soils are almost quantitatively depleted 946 00:53:43,160 --> 00:53:37,810 of pass him yep 947 00:53:50,130 --> 00:53:47,670 we have another question in art I know 948 00:53:52,560 --> 00:53:50,140 him this is Dave again I had a question 949 00:53:54,240 --> 00:53:52,570 it's so the idea is that maybe the super 950 00:53:56,190 --> 00:53:54,250 earth would be rather like the ad on 951 00:53:58,230 --> 00:53:56,200 earth that but maybe persisting for a 952 00:53:59,730 --> 00:53:58,240 longer period of time in that state but 953 00:54:01,950 --> 00:53:59,740 then the flip side of that is that the 954 00:54:04,140 --> 00:54:01,960 ad and earth might be rather like the 955 00:54:06,030 --> 00:54:04,150 super planet in the sense that you'd 956 00:54:07,740 --> 00:54:06,040 have this pervasive ocean so do you 957 00:54:09,690 --> 00:54:07,750 think that actually is some insight for 958 00:54:12,870 --> 00:54:09,700 the nature of the Haidee and earth in 959 00:54:17,790 --> 00:54:12,880 this I think so that it 960 00:54:20,310 --> 00:54:17,800 we might not has been probably not as 961 00:54:23,960 --> 00:54:20,320 reducing on the hit a and earth we 962 00:54:26,280 --> 00:54:23,970 probably did not get a Percival wide 963 00:54:30,240 --> 00:54:26,290 continent even though people of argue 964 00:54:39,270 --> 00:54:30,250 that we did that's just mass balance 965 00:54:43,110 --> 00:54:39,280 unlikely and we may have well had they 966 00:54:47,540 --> 00:54:43,120 at least appeared in our kyun something 967 00:54:51,030 --> 00:54:47,550 were exterminated by volcanic s-- rather 968 00:54:53,270 --> 00:54:51,040 than by plates but in the D in 969 00:54:58,610 --> 00:54:53,280 particular people have even argued that 970 00:55:02,480 --> 00:54:58,620 for the okiya we get surface weathering 971 00:55:05,490 --> 00:55:02,490 probably by 3/8 sensors well-preserved 972 00:55:08,460 --> 00:55:05,500 shales with sedimentary structures by 973 00:55:11,820 --> 00:55:08,470 them and arguments from the Zutons that 974 00:55:15,960 --> 00:55:11,830 we have some surficial weathering a33 of 975 00:55:18,870 --> 00:55:15,970 4-3 or so so not a complete a toward the 976 00:55:23,160 --> 00:55:18,880 tectonically somewhat of a like the 977 00:55:27,750 --> 00:55:23,170 earth gets hot not hot enough inside and 978 00:55:30,060 --> 00:55:27,760 enough heat loss radioactivity plate 979 00:55:44,830 --> 00:55:30,070 tectonics or the simple form is no 980 00:55:51,710 --> 00:55:49,130 about that if you're in the limit of 981 00:55:58,270 --> 00:55:51,720 diffusion limited hydrogen escape which 982 00:56:11,030 --> 00:56:01,400 that's governed by buoyancy so the 983 00:56:24,650 --> 00:56:11,040 bigger the gravity of separating 984 00:56:26,630 --> 00:56:24,660 hydrogen okay okay baby rock I get 985 00:56:42,650 --> 00:56:26,640 Jeffers how about a stroke needs to do 986 00:56:44,810 --> 00:56:42,660 this worse even if it's not the soup 987 00:56:47,050 --> 00:56:44,820 earth were considering what a very 988 00:56:50,540 --> 00:56:47,060 reduced end of a planet would be we have 989 00:56:54,500 --> 00:56:50,550 we have Titan on our own solar system 990 00:56:59,090 --> 00:56:54,510 that does not have a silicate surface 991 00:57:02,600 --> 00:56:59,100 but may well have a water ocean so if we 992 00:57:04,610 --> 00:57:02,610 go deep enough into Titan we start to 993 00:57:06,500 --> 00:57:04,620 approach these conditions even on the 994 00:57:11,960 --> 00:57:06,510 inside is probably not extremely 995 00:57:11,970 --> 00:57:16,849 okay Jim you have your assignment Oh 996 00:57:26,010 --> 00:57:20,099 long do you want to say anything about 997 00:57:37,230 --> 00:57:26,020 that well I'd love to do that some kind 998 00:57:41,640 --> 00:57:37,240 of hard to do okay do we have any other 999 00:57:43,530 --> 00:57:41,650 hands raised Marco and WebEx okay if 1000 00:57:45,480 --> 00:57:43,540 anybody would like to just jump in with 1001 00:57:49,920 --> 00:57:45,490 the question just open your mic and go 1002 00:57:51,540 --> 00:57:49,930 ahead Noren to say again add the 1003 00:57:53,400 --> 00:57:51,550 question about the Hadean on the earth 1004 00:57:56,700 --> 00:57:53,410 do you think the more globally pervasive 1005 00:58:02,370 --> 00:57:56,710 ocean is an interesting concept that has 1006 00:58:05,760 --> 00:58:02,380 some merit to it enough we call Galileo 1007 00:58:10,710 --> 00:58:05,770 this kind of a subtle effect here that 1008 00:58:13,579 --> 00:58:10,720 the Obito of the ocean is lower than the 1009 00:58:15,839 --> 00:58:13,589 albedo of the terrestrial deserts 1010 00:58:23,210 --> 00:58:15,849 apparently this is visible with the 1011 00:58:27,660 --> 00:58:23,220 naked eye when the crescent moon is over 1012 00:58:29,460 --> 00:58:27,670 the terrestrial deserts the earth shine 1013 00:58:31,559 --> 00:58:29,470 is brighter than when it's over the 1014 00:58:35,599 --> 00:58:31,569 ocean this is in Galileo and the 1015 00:58:40,079 --> 00:58:35,609 dialogues so this is at least a partial 1016 00:58:45,329 --> 00:58:40,089 way around their weak young Sun paradox 1017 00:58:47,490 --> 00:58:45,339 is that a mostly ocean covered planet 1018 00:58:51,720 --> 00:58:47,500 would have sard morrow of a sunlight 1019 00:58:54,390 --> 00:58:51,730 rather than reflective and there's also 1020 00:58:58,800 --> 00:58:54,400 a daisyworld thing here for the earth if 1021 00:59:01,620 --> 00:58:58,810 we have a anoxygenic or the iron based 1022 00:59:06,000 --> 00:59:01,630 photosynthetic microbial mat covering 1023 00:59:10,440 --> 00:59:06,010 the planets desert front as a law albedo 1024 00:59:13,380 --> 00:59:10,450 compared to reflective still desert the 1025 00:59:15,680 --> 00:59:13,390 Egyptians raised goats they've been able 1026 00:59:19,230 --> 00:59:15,690 to get rid of the desert crust in the 1027 00:59:24,030 --> 00:59:19,240 Sinai and it's 2 degrees centigrade or 1028 00:59:27,840 --> 00:59:24,040 than the Israeli Sinai where they 1029 00:59:31,770 --> 00:59:27,850 now over grazing braig um so you can end 1030 00:59:34,800 --> 00:59:31,780 up with this daisyworld situation where 1031 00:59:37,110 --> 00:59:34,810 the microbial mats will spread warming 1032 00:59:39,030 --> 00:59:37,120 the temperature of the planet and do 1033 00:59:41,010 --> 00:59:39,040 they cover enough of the planet that 1034 00:59:43,880 --> 00:59:41,020 they get warm enough that they're 1035 00:59:47,760 --> 00:59:43,890 limited by desiccation and then this 1036 00:59:50,160 --> 00:59:47,770 stable buffer of temperature will occur 1037 00:59:51,540 --> 00:59:50,170 at the point of desiccation at the warm 1038 00:59:54,330 --> 00:59:51,550 end of the daisyworld 1039 00:59:58,800 --> 00:59:54,340 rather than the cold freezing it so 1040 01:00:04,320 --> 00:59:58,810 there is a potential Gihon like 1041 01:00:07,590 --> 01:00:04,330 mechanism here I think there's a work of 1042 01:00:12,780 --> 01:00:07,600 Blair hedges on the family tree alight 1043 01:00:15,720 --> 01:00:12,790 some evidence of cyanobacteria evolved 1044 01:00:18,540 --> 01:00:15,730 on land from soil bacteria and fire and 1045 01:00:22,280 --> 01:00:18,550 evolved from an ecosystem that 1046 01:00:24,720 --> 01:00:22,290 originally and it was doing an toxigenic 1047 01:00:29,040 --> 01:00:24,730 photosynthesis so probably thoroughly 1048 01:00:31,770 --> 01:00:29,050 early on before 3/8 we had the 1049 01:00:37,250 --> 01:00:31,780 continents covered by these micro 1050 01:00:40,440 --> 01:00:37,260 pervasive microbial mats anoxygenic 1051 01:00:43,620 --> 01:00:40,450 photosynthesis getting the iron out is a 1052 01:00:49,290 --> 01:00:43,630 big prize you need four irons to make 1053 01:00:51,630 --> 01:00:49,300 one organic carbon so we may have had an 1054 01:00:54,480 --> 01:00:51,640 ethical system that would have evolved 1055 01:00:59,190 --> 01:00:54,490 and eventually ended up with the soil 1056 01:01:03,090 --> 01:00:59,200 bacteria cyanobacteria would evolve to 1057 01:01:05,550 --> 01:01:03,100 be able to inhabit low ion Regents that 1058 01:01:07,440 --> 01:01:05,560 were the AFOL to the eventual weathering 1059 01:01:10,560 --> 01:01:07,450 melting and tectonics whole iron 1060 01:01:13,710 --> 01:01:10,570 Granite's low iron shales borne court 1061 01:01:16,290 --> 01:01:13,720 sites where there would be a strong 1062 01:01:22,380 --> 01:01:16,300 selective pressure for an organism with 1063 01:01:25,950 --> 01:01:22,390 that ability and the evidence for this 1064 01:01:29,910 --> 01:01:25,960 is that the cyanobacteria seem to be 1065 01:01:32,210 --> 01:01:29,920 related to bacteria that are originally 1066 01:01:35,819 --> 01:01:32,220 and still primarily have a 1067 01:01:38,700 --> 01:01:35,829 all probably combining through organisms 1068 01:01:41,279 --> 01:01:38,710 that have the ability inadvertently to 1069 01:01:45,809 --> 01:01:41,289 make a little bit of oxygen and when it 1070 01:01:49,380 --> 01:01:45,819 gets the ability to make a lot of any 1071 01:01:52,890 --> 01:01:49,390 bit more becomes valuable each oxygen 1072 01:01:55,380 --> 01:01:52,900 you make that means you don't even need 1073 01:01:57,870 --> 01:01:55,390 for ions which is a big deal when you in 1074 01:02:02,160 --> 01:01:57,880 your iron limited in the ocean there be 1075 01:02:04,140 --> 01:02:02,170 iron and sulfide around so the it 1076 01:02:08,370 --> 01:02:04,150 becomes less advantageous to do an 1077 01:02:10,980 --> 01:02:08,380 oxygen photosynthesis you the producing 1078 01:02:14,430 --> 01:02:10,990 an oxidant that you don't immediately 1079 01:02:16,620 --> 01:02:14,440 get back yourself it's not it does not 1080 01:02:23,430 --> 01:02:16,630 become a storehouse of energy so it 1081 01:02:26,609 --> 01:02:23,440 becomes beyond my new quantity in the 1082 01:02:30,960 --> 01:02:26,619 air if you forgive ferric iron and it 1083 01:02:33,809 --> 01:02:30,970 stays around microbial mat you get 1084 01:02:36,359 --> 01:02:33,819 benefit from that your close call no 1085 01:02:37,740 --> 01:02:36,369 relatives benefit from that oxidant that 1086 01:02:42,840 --> 01:02:37,750 you've just made if you can do the 1087 01:02:42,850 --> 01:02:48,810 any more questions 1088 01:02:56,970 --> 01:02:53,450 okay then let me remind you that the 1089 01:02:59,400 --> 01:02:56,980 this seminar will be archived it'll be 1090 01:03:01,680 --> 01:02:59,410 available and up on the NA our website 1091 01:03:04,830 --> 01:03:01,690 probably in about 3-4 days certainly by 1092 01:03:07,020 --> 01:03:04,840 next week and anybody who missed it this 1093 01:03:10,100 --> 01:03:07,030 time or who wants to hear it again will 1094 01:03:13,860 --> 01:03:10,110 have the opportunity to in perpetuity 1095 01:03:15,960 --> 01:03:13,870 and once again the next nai director 1096 01:03:17,460 --> 01:03:15,970 seminar will be given by Jack szostak of 1097 01:03:20,730 --> 01:03:17,470 Hubbard University in Massachusetts 1098 01:03:23,190 --> 01:03:20,740 General Hospital and that will be on 1099 01:03:27,480 --> 01:03:23,200 Monday November 3rd same time same 1100 01:03:33,360 --> 01:03:27,490 channel and one last opportunity for 1101 01:03:40,470 --> 01:03:33,370 questions to norm going once going twice