1 00:00:03,560 --> 00:00:06,520 This is Geology Bites with Oliver Strimpel. 2 00:00:07,920 --> 00:00:11,960 When the Earth formed, it was covered by a hot magma ocean. 3 00:00:12,920 --> 00:00:17,000 At some point it cooled enough to form a solid surface thought 4 00:00:17,000 --> 00:00:21,320 to be basaltic in composition, like today's oceanic crust. 5 00:00:22,160 --> 00:00:26,120 Then at some point the surface began to differentiate into 6 00:00:26,120 --> 00:00:30,840 different types of lithosphere, basaltic oceanic lithosphere, 7 00:00:31,360 --> 00:00:34,520 and more silica rich continental lithosphere. 8 00:00:35,880 --> 00:00:39,960 How did this process occur? Were the first ancient 9 00:00:39,960 --> 00:00:43,960 continents similar to the present day continents and did 10 00:00:43,960 --> 00:00:47,400 the continents form in a burst of activity at a certain point 11 00:00:47,400 --> 00:00:51,440 when differentiation occurred, or was it a gradual build up 12 00:00:51,440 --> 00:00:56,120 over Earth history? Renee Tamblyn studies the early 13 00:00:56,120 --> 00:01:00,560 Earth and in particular the role of water in the formation of 14 00:01:00,560 --> 00:01:03,800 continents. She's also exploring how the 15 00:01:03,800 --> 00:01:07,160 production of hydrogen from geological processes could have 16 00:01:07,160 --> 00:01:09,880 powered very early forms of life. 17 00:01:10,880 --> 00:01:14,320 She's a postdoctoral researcher at the University of Bern. 18 00:01:15,640 --> 00:01:18,560 Renee Tamblyn, welcome to Geology Bites. 19 00:01:18,960 --> 00:01:21,560 Thank you very much, Oliver. It's an honour to be here. 20 00:01:22,200 --> 00:01:25,800 Before we talk about how continents form, how confident 21 00:01:25,800 --> 00:01:30,480 are we that the basic picture I laid out just now is correct, 22 00:01:30,880 --> 00:01:34,440 namely that the Earth was born without any continents and that 23 00:01:34,440 --> 00:01:37,120 these had to form at some later point in Earth history? 24 00:01:37,760 --> 00:01:40,840 So although we don't have any rocks preserved from the 25 00:01:40,840 --> 00:01:45,320 earliest part of the Earth, so particularly from about 4.56 26 00:01:45,320 --> 00:01:49,440 billion years ago when the Earth was first accreted, until about 27 00:01:49,440 --> 00:01:53,120 4 billion years ago, which is the oldest rock we have, we 28 00:01:53,200 --> 00:01:56,000 don't really have any picture of what the Earth may have looked 29 00:01:56,000 --> 00:01:57,560 like then because it's not preserved. 30 00:01:58,320 --> 00:02:01,480 But I think we are quite confident that the Earth 31 00:02:01,480 --> 00:02:03,600 certainly started as a magma ocean. 32 00:02:03,680 --> 00:02:06,720 And we know that from this magma ocean we could not make the 33 00:02:06,720 --> 00:02:10,680 continents, as you mentioned, these silica rich continents. 34 00:02:10,680 --> 00:02:14,280 They need much more complex geological processes to form 35 00:02:14,400 --> 00:02:17,120 rather than just forming from a simple magma ocean. 36 00:02:18,400 --> 00:02:22,480 So we know that at some point, and when is the big question, 37 00:02:22,480 --> 00:02:25,680 these continents first emerged, that there must have been more 38 00:02:26,000 --> 00:02:29,120 difficult, more complex geological processes at play 39 00:02:29,560 --> 00:02:32,240 that allowed these continents to differentiate. 40 00:02:33,480 --> 00:02:36,240 And we know this because the chemical components which make 41 00:02:36,240 --> 00:02:38,920 up the continental crust are very different from the oceanic 42 00:02:38,920 --> 00:02:42,480 crust, or what would have been quite similar to this magma 43 00:02:42,480 --> 00:02:46,320 ocean at the beginning. The continents today are quite 44 00:02:46,320 --> 00:02:48,000 different from the continents in the past. 45 00:02:48,000 --> 00:02:51,120 The continents today are very rich in elements as such as 46 00:02:51,120 --> 00:02:54,720 silica as you mentioned, but also potassium, whereas the 47 00:02:54,720 --> 00:02:57,640 earliest continents, the ones from the Archaean, so this is 48 00:02:57,640 --> 00:03:01,600 the time frame from 4 billion years ago to 2.5 billion years 49 00:03:01,600 --> 00:03:06,120 ago, tend to be more rich in elements such as sodium and 50 00:03:06,120 --> 00:03:09,800 calcium. So this leads us to think that 51 00:03:10,000 --> 00:03:12,720 the processes we see today making our continents, our 52 00:03:12,720 --> 00:03:15,440 potassium rich continents must have been quite different to the 53 00:03:15,440 --> 00:03:17,480 processes we saw in the Archaean. 54 00:03:18,800 --> 00:03:22,360 Finally, the question of when the continental crust actually 55 00:03:22,360 --> 00:03:27,080 formed is a huge question. And at Sciences, because as I 56 00:03:27,080 --> 00:03:30,160 mentioned, we don't have a record from the 1st 500 million 57 00:03:30,160 --> 00:03:34,400 years or so, but also it's a question between formation and 58 00:03:34,400 --> 00:03:37,680 preservation. So we know we can form the 59 00:03:37,680 --> 00:03:41,600 continents, but we also know they can be destroyed, they can 60 00:03:41,640 --> 00:03:45,160 either be eroded or they can be buried back into the mantle and 61 00:03:45,160 --> 00:03:48,720 lost to our geological record. So it's a balance between 62 00:03:48,720 --> 00:03:53,320 creation and preservation. OK, so let's actually talk about 63 00:03:53,320 --> 00:03:58,400 how continents form. Do any of the first continents 64 00:03:58,400 --> 00:04:01,720 survive to the present day to give us some clues as to how 65 00:04:01,720 --> 00:04:04,640 they formed? So we do have evidence of some 66 00:04:04,640 --> 00:04:09,080 very, very ancient continents on the Earth, Luckily for us, and 67 00:04:09,080 --> 00:04:11,000 as I mentioned, they're quite different to the younger 68 00:04:11,000 --> 00:04:14,160 continents we see today. And this difference has spurred 69 00:04:14,160 --> 00:04:17,720 a massive amount of research into these earliest continents. 70 00:04:17,720 --> 00:04:20,040 We don't know if they were the first ones, but we certainly 71 00:04:20,040 --> 00:04:22,000 hope they were some of the first ones. 72 00:04:22,520 --> 00:04:25,360 And these give us a lot of clues. 73 00:04:25,560 --> 00:04:28,440 But it's kind of like you have an end product and you have to 74 00:04:28,440 --> 00:04:30,760 go back and work out how it was formed, What were the 75 00:04:30,760 --> 00:04:32,920 ingredients, what was the recipe to make it. 76 00:04:33,760 --> 00:04:36,920 And there's a few important things that we need to know. 77 00:04:37,320 --> 00:04:40,720 We need to know the source rock because you can't create a rock 78 00:04:40,720 --> 00:04:42,560 from nothing. There had to be some rock there 79 00:04:42,560 --> 00:04:45,040 before that was affected to create the continent. 80 00:04:45,040 --> 00:04:47,640 In this case probably melted or re melted. 81 00:04:48,760 --> 00:04:52,000 And we also need to know what exact process did that, which is 82 00:04:52,000 --> 00:04:56,240 that process modified, it re melted it to make the continents 83 00:04:56,240 --> 00:05:00,120 that we see preserved now. And we think that either the 84 00:05:00,120 --> 00:05:04,200 starting composition or the process, both or one of them at 85 00:05:04,200 --> 00:05:06,000 least were different in the RTN to now. 86 00:05:07,080 --> 00:05:10,520 Can we date the oldest continental cross fairly 87 00:05:10,520 --> 00:05:12,960 confidently? Yes, we can. 88 00:05:13,040 --> 00:05:16,800 So as I mentioned, the oldest rock we have is 4 billion years 89 00:05:16,800 --> 00:05:19,160 old, but that's a small amount of rock. 90 00:05:19,880 --> 00:05:23,120 But the first continents we can really find on Earth seem to be 91 00:05:23,120 --> 00:05:26,800 around 3.8 billion years ago. And then we have them all 92 00:05:26,800 --> 00:05:29,600 throughout the Archaeans. So we also have some nice ones 93 00:05:29,600 --> 00:05:32,800 around 3.4 billion years ago, 3.2 billion years ago. 94 00:05:32,800 --> 00:05:35,200 So we seem to have a good picture of the continents 95 00:05:35,400 --> 00:05:39,160 throughout the Archaean. What can we learn about the 96 00:05:39,160 --> 00:05:42,520 processes that took place at the beginning and formed the first 97 00:05:42,520 --> 00:05:45,880 continents? Yes, If we go and look now, so 98 00:05:46,080 --> 00:05:48,720 interestingly, these are key and bits of rock. 99 00:05:48,720 --> 00:05:51,920 They only cover about 8% of the continents we have now. 100 00:05:52,120 --> 00:05:55,160 So we find these are cratons, they're all over the world 101 00:05:55,160 --> 00:05:58,360 amazingly, but some of the oldest ones and the ones which 102 00:05:58,360 --> 00:06:02,280 have had the most study, the most well preserved are in North 103 00:06:02,280 --> 00:06:06,240 America, the superior craton. We have very famous the couple 104 00:06:06,240 --> 00:06:10,200 craton which is in South Africa. And there's also several cratons 105 00:06:10,200 --> 00:06:14,160 in Australia, which are particularly old, many in India, 106 00:06:14,440 --> 00:06:17,720 Central Asia, China and also in South America. 107 00:06:18,840 --> 00:06:24,320 And they are 80% dominated by one series of rocks, one 108 00:06:24,320 --> 00:06:27,800 magmatic series of rocks. And we call these TTGS, which 109 00:06:27,800 --> 00:06:30,240 stands for Tonalite Trundumite granodiarides. 110 00:06:30,280 --> 00:06:32,120 Say that a bit more slowly for me. 111 00:06:32,440 --> 00:06:36,560 Way too fast. Tonalite trundumite 112 00:06:36,560 --> 00:06:39,760 granodiaride. So these tonalite, trundumite 113 00:06:39,760 --> 00:06:42,640 granodiarides, they're magmatic rocks, they're igneous, they're 114 00:06:42,640 --> 00:06:44,720 melted and they crystallize in the crust. 115 00:06:45,440 --> 00:06:48,760 And these are these very high silica rocks, very high in 116 00:06:48,760 --> 00:06:52,000 sodium, very high in calcium, and importantly, they're not 117 00:06:52,000 --> 00:06:53,680 very dense, they're very buoyant. 118 00:06:53,840 --> 00:06:56,040 This is what actually makes the continent, the fact that they're 119 00:06:56,040 --> 00:06:59,480 buoyant and thick and therefore are above the ocean. 120 00:07:00,680 --> 00:07:04,720 So these TTGS, as we call them, we like to shorten it. 121 00:07:06,120 --> 00:07:09,480 They seem to require sort of three things to form. 122 00:07:10,200 --> 00:07:13,360 First of all, we need a starting rock, as I said, something that 123 00:07:13,360 --> 00:07:16,720 they had created from, and in this case we know it's a basalt. 124 00:07:16,720 --> 00:07:21,160 They come from the melting or remelting of basalts or mafic 125 00:07:21,160 --> 00:07:23,840 rocks, as we also say. So these are rocks that are high 126 00:07:23,840 --> 00:07:28,480 in magnesium and iron. They also require temperature. 127 00:07:28,480 --> 00:07:31,520 To melt a basalt, you need to take it to fairly high 128 00:07:31,520 --> 00:07:36,200 temperatures, to more than 708 hundred degrees Celsius, but 129 00:07:36,200 --> 00:07:39,280 intriguingly, not that high temperature, so maybe less than 130 00:07:39,280 --> 00:07:42,000 900°C. Prosteologist. 131 00:07:42,000 --> 00:07:46,720 That's not too hot. And lastly, they seem to require 132 00:07:46,840 --> 00:07:51,080 water, which is an interesting thing, free water in these 133 00:07:51,080 --> 00:07:56,200 rocks. These cratons are mostly TTGS, 134 00:07:56,200 --> 00:07:58,200 but they're not entirely TTGS, are they? 135 00:07:58,720 --> 00:08:01,800 No, they're not. Around 80% seem to be the other 136 00:08:01,800 --> 00:08:06,360 20%, a series of rocks which we refer to as greenstone belts. 137 00:08:06,920 --> 00:08:09,600 And greenstone comes from the fact that these rocks tend to be 138 00:08:09,600 --> 00:08:12,440 green, very inventive, but they're actually super 139 00:08:12,440 --> 00:08:14,920 interesting. They're very diverse, unlike our 140 00:08:14,920 --> 00:08:18,880 TTGS, and they seem to be primarily made of volcanic 141 00:08:18,880 --> 00:08:23,640 rocks, so rocks which erupted. And these, unlike the TTGS, are 142 00:08:23,640 --> 00:08:26,440 not so rich in silica. They're actually very, very 143 00:08:26,440 --> 00:08:28,680 mafic. So they have high amounts of 144 00:08:28,680 --> 00:08:32,480 magnesium and iron. And the rest of these TTGS, 145 00:08:32,480 --> 00:08:34,799 where it's not volcanic, tend to be sedimentary. 146 00:08:34,840 --> 00:08:37,760 So we have a lot of sedimentary rocks also preserved in these 147 00:08:37,760 --> 00:08:42,120 greenstone belts. So mostly these TTGS, but a 148 00:08:42,120 --> 00:08:46,080 certain number of these high magnesium volcanic rocks, those 149 00:08:46,080 --> 00:08:48,160 are referred to as chromatiates, aren't they? 150 00:08:48,400 --> 00:08:50,640 Yes, true, including cholateates. 151 00:08:50,840 --> 00:08:54,440 That's my current area of work for the past four years is 152 00:08:54,440 --> 00:08:57,640 looking at these rocks called Commadiites, which is a great 153 00:08:57,640 --> 00:09:01,600 name named after a place called the Kamati River in South 154 00:09:01,600 --> 00:09:03,640 Africa. And these are really strange 155 00:09:03,640 --> 00:09:08,040 rocks because they are lavas and they're incredibly magnesium, so 156 00:09:08,040 --> 00:09:10,680 20 plus weight percent magnesium, which is a lot. 157 00:09:11,440 --> 00:09:15,600 And interestingly, they seem to have erupted at extremely high 158 00:09:15,600 --> 00:09:21,240 temperatures, so maybe 1600°C, which is incredibly toasty. 159 00:09:22,440 --> 00:09:25,600 And these incredibly high temperatures seem to come from 160 00:09:25,600 --> 00:09:28,920 the fact that commodities were generated very deep in the 161 00:09:28,920 --> 00:09:32,080 mantle, actually probably very close to the mantle core 162 00:09:32,080 --> 00:09:34,720 boundary. And they then ascend through the 163 00:09:34,720 --> 00:09:38,600 mantle as a mantle plume and erupt in the arcane to form 164 00:09:38,600 --> 00:09:42,280 these commodities. And we don't find them really 165 00:09:42,280 --> 00:09:44,320 post Archaean. There are some very rare 166 00:09:44,320 --> 00:09:46,720 examples, but most of them in the Archaean. 167 00:09:46,920 --> 00:09:50,000 So it seems to be something very special to the Archaean. 168 00:09:50,440 --> 00:09:53,200 And that is because, simply, the Earth was a lot hotter back 169 00:09:53,200 --> 00:09:56,560 then. Does the disappearance of 170 00:09:57,120 --> 00:10:00,800 Comatia and TT GS I guess does that happen at a particular time 171 00:10:00,800 --> 00:10:03,520 in Earth history then? Yes, absolutely. 172 00:10:03,960 --> 00:10:08,880 So it's very intriguing that the TTGS, they seem to die out after 173 00:10:08,880 --> 00:10:13,240 the Ikeans. So from 2 billion years is some 174 00:10:13,240 --> 00:10:16,640 of the last big swaths of them, the Commadiites become 175 00:10:16,640 --> 00:10:19,880 incredibly rare after 2.5 billion years. 176 00:10:19,880 --> 00:10:22,640 So they seem to have really dominated the geological record 177 00:10:22,640 --> 00:10:26,360 in the Ikean and then they suddenly start to really die out 178 00:10:26,360 --> 00:10:29,000 and become less well preserved in the geological record. 179 00:10:29,360 --> 00:10:32,120 And do we have a theory as to why that is? 180 00:10:33,000 --> 00:10:35,840 For the commodities, the idea seems to be that the earth 181 00:10:35,840 --> 00:10:38,680 cooled beyond some kind of tipping point. 182 00:10:39,280 --> 00:10:41,720 So the earth at the beginning was very warm thanks to its 183 00:10:41,720 --> 00:10:45,120 accretion, the kinetic force of accretion, and also from the 184 00:10:45,120 --> 00:10:48,880 decay of radioactive elements which slowly died out over time. 185 00:10:49,400 --> 00:10:53,560 So it seems around 2.5 to 2 billion years some sort of 186 00:10:53,560 --> 00:10:56,760 switch went off. Suddenly the Earth cooled to 187 00:10:56,760 --> 00:10:59,600 some point where we weren't making these commodities, these 188 00:10:59,600 --> 00:11:01,880 ultra hot mantle plumes as much anymore. 189 00:11:02,600 --> 00:11:05,720 Intriguingly, this also corresponds to some very 190 00:11:05,720 --> 00:11:09,160 significant atmospheric events, but maybe we can touch on that 191 00:11:09,160 --> 00:11:11,040 later. So I'm trying to form a picture 192 00:11:11,040 --> 00:11:14,280 then. So we have these TTGS which were 193 00:11:14,760 --> 00:11:17,360 platonic rocks. They're part of that ranatoid 194 00:11:17,360 --> 00:11:20,280 family on the one hand. And then you have the volcanic 195 00:11:20,280 --> 00:11:24,840 rocks that I guess spewed out over them, the high magnesium 196 00:11:24,960 --> 00:11:29,480 comatiites, and then sedimentary rocks as well, which I guess are 197 00:11:29,480 --> 00:11:33,000 secondary processes. And then after the end of the 198 00:11:33,000 --> 00:11:38,280 Archaean, some new or slightly altered processes took place to 199 00:11:38,280 --> 00:11:40,240 continue to build the continents. 200 00:11:40,240 --> 00:11:42,400 Is that right? I think that's a very good way 201 00:11:42,400 --> 00:11:45,280 of phrasing it. Some people might say that that 202 00:11:45,280 --> 00:11:48,120 could be actually the emergence of plate tectonics. 203 00:11:48,360 --> 00:11:51,520 And when I say plate tectonics, I mean modern plate tectonics. 204 00:11:51,520 --> 00:11:55,960 So where we have very stiff rigid plates and very deep and 205 00:11:55,960 --> 00:11:59,160 very steep subductions when the oceanic plate is thrust under 206 00:11:59,160 --> 00:12:03,160 the continental plate and a lot of pupils align that with the 207 00:12:03,160 --> 00:12:06,240 end of the reign of TTGS and commodities. 208 00:12:06,240 --> 00:12:08,560 I personally think the picture is a little bit more 209 00:12:08,560 --> 00:12:11,840 complicated. I think we have local examples 210 00:12:11,840 --> 00:12:16,000 of subduction and some sort of horizontal tectonics, probably 211 00:12:16,000 --> 00:12:18,600 in the Archaean, but there does some seem to be some major 212 00:12:18,600 --> 00:12:21,200 change. As I mentioned, you're 213 00:12:21,200 --> 00:12:24,680 especially interested in the role of water in the process of 214 00:12:24,680 --> 00:12:28,040 forming continental crust. Can you tell us about that? 215 00:12:28,320 --> 00:12:31,800 Yes. So water is a vital ingredient 216 00:12:31,800 --> 00:12:34,560 in the continental crust, whether it be in the ancient 217 00:12:34,560 --> 00:12:36,960 earth, in the Archaean or in the modern earth. 218 00:12:38,120 --> 00:12:42,200 And the key thing is how do we get the water to high 219 00:12:42,200 --> 00:12:44,480 temperatures? Because what we really need is 220 00:12:44,480 --> 00:12:48,040 water to lower the solidus of rocks like basalts, IE make 221 00:12:48,040 --> 00:12:51,280 melting of these rocks or re melting of these rocks easier 222 00:12:52,240 --> 00:12:55,480 because that's how we form either our TTGS in the Archaean 223 00:12:55,480 --> 00:12:57,320 or our granites in the modern Earth. 224 00:12:57,800 --> 00:13:01,200 There's been a lot of research looking into the sorts of rocks 225 00:13:01,200 --> 00:13:04,560 that might be able to carry this water capture in the crystal 226 00:13:04,560 --> 00:13:07,680 structure and also carry this water to higher temperatures. 227 00:13:08,080 --> 00:13:10,840 And by high temperatures I mean more than 700°. 228 00:13:10,840 --> 00:13:16,040 So the temperatures of melting of these vessels in the modern 229 00:13:16,040 --> 00:13:18,080 Earth. We understand this very well in 230 00:13:18,080 --> 00:13:22,280 subduction zones where we have oceanic crust which is being 231 00:13:22,280 --> 00:13:26,200 pushed down into the mantle, but in the Ikean this is a bit more 232 00:13:26,200 --> 00:13:30,080 of an unknown. You mentioned the solidus, so 233 00:13:30,920 --> 00:13:36,040 when rocks are wet, the solidus is lower, which means they melt 234 00:13:36,040 --> 00:13:37,760 at much lower temperatures. Is that right? 235 00:13:38,200 --> 00:13:42,400 Precisely, yes, and also they tend to melt in larger volumes. 236 00:13:42,400 --> 00:13:45,960 It's a very simple equation, but the more water you put into a 237 00:13:45,960 --> 00:13:48,360 rock, the more it melts and the more you can extract. 238 00:13:48,920 --> 00:13:50,960 And of course what we're interested in is this 239 00:13:50,960 --> 00:13:55,280 extraction, which is what forms Astorica rich, calcium rich and 240 00:13:55,280 --> 00:13:59,360 sodium rich rocks. So I would say the best way to 241 00:13:59,360 --> 00:14:03,960 make a continent is add water. So would it be fair to say that 242 00:14:03,960 --> 00:14:07,920 if you didn't have the water a you wouldn't have the volume of 243 00:14:07,920 --> 00:14:12,520 rocks formed that we see, and B they would have a different 244 00:14:12,520 --> 00:14:17,840 composition because of the kind of partial melting that takes 245 00:14:17,840 --> 00:14:19,520 place? Perfectly said. 246 00:14:19,520 --> 00:14:22,480 Yes, If we didn't have water travelling into our crust and 247 00:14:22,480 --> 00:14:25,720 travelling into our mantle, we would have a very different 248 00:14:25,720 --> 00:14:28,120 world. We would probably have smaller 249 00:14:28,120 --> 00:14:30,960 continents, as you said, because they'd be less volume and they 250 00:14:30,960 --> 00:14:33,920 would have a very different composition because the melting 251 00:14:33,920 --> 00:14:36,760 reactions, the reactions of different minerals to create 252 00:14:36,760 --> 00:14:38,200 that would be radically different. 253 00:14:39,240 --> 00:14:44,840 Is the water part of the story as to why we don't see TCGS 254 00:14:44,840 --> 00:14:47,760 forming later? That just wasn't enough water to 255 00:14:47,760 --> 00:14:52,000 form that kind of Celtic rock. Oh, that's a very interesting 256 00:14:52,000 --> 00:14:55,200 question. So we know that water is very 257 00:14:55,200 --> 00:14:58,840 important in making granites. Actually, this is only an idea 258 00:14:58,840 --> 00:15:02,480 that's really come around in the past 25 years or so or 30 years. 259 00:15:02,560 --> 00:15:05,080 We're understanding how important water in the crust is, 260 00:15:05,840 --> 00:15:09,000 and most granites, especially the granites which we see being 261 00:15:09,000 --> 00:15:12,600 made today, say in volcanic arcs, actually do have a lot of 262 00:15:12,600 --> 00:15:15,960 water in their source region. The water just comes from 263 00:15:15,960 --> 00:15:18,160 seduction zones. It comes from seduction of 264 00:15:18,160 --> 00:15:23,360 oceanic crust. The switch between TTGS and 265 00:15:23,360 --> 00:15:27,840 granites is, I think, a little bit more messy than that. 266 00:15:28,440 --> 00:15:31,720 I think it could be looking at a change in thermal regime. 267 00:15:31,920 --> 00:15:36,400 So the Archaean being hotter, it could be a source problem. 268 00:15:36,400 --> 00:15:40,320 So the basalts forming the TTGS could have a very different 269 00:15:40,320 --> 00:15:44,600 composition to the basalts and ultramipic rocks which granites 270 00:15:44,600 --> 00:15:47,240 come from. And it could also be plate 271 00:15:47,240 --> 00:15:50,160 tectonics. You go from modern, right now we 272 00:15:50,160 --> 00:15:54,000 have this, as I said, this very steep cold subduction which 273 00:15:54,000 --> 00:15:57,320 seems to release water which eventually creates a granite. 274 00:15:58,040 --> 00:16:00,960 Whereas in the Archaean, perhaps we didn't have that, perhaps we 275 00:16:00,960 --> 00:16:04,480 had more collision or shallow hot subduction. 276 00:16:04,800 --> 00:16:07,840 So there's really all these different things which come into 277 00:16:07,840 --> 00:16:10,000 play. So if you melt the bath salts 278 00:16:10,000 --> 00:16:15,560 and you make TTGS early on, it's a very similar process that 279 00:16:15,560 --> 00:16:20,880 produces the granites of today, but they have less magnesium in 280 00:16:20,880 --> 00:16:21,600 them. Is that right? 281 00:16:22,320 --> 00:16:24,880 Yeah, it's kind of really hard to put the finger on this 282 00:16:24,880 --> 00:16:28,200 because there's like 3 or 4 different reasons why that's the 283 00:16:28,200 --> 00:16:30,760 case. So it's like kind of all tangled 284 00:16:30,760 --> 00:16:32,920 up. But yes, it's a similar process 285 00:16:33,080 --> 00:16:35,160 to now. It just seems that these 286 00:16:35,160 --> 00:16:37,480 different ingredients, the starting composition and the 287 00:16:37,480 --> 00:16:41,120 processes seem to be different. But water seems to be the key 288 00:16:41,120 --> 00:16:43,640 player all throughout the Earth's history. 289 00:16:44,360 --> 00:16:47,160 It's just a question of how do you get the water to those 290 00:16:47,160 --> 00:16:49,920 temperatures? What is the main difference then 291 00:16:49,960 --> 00:16:54,520 between T2 GS and modern day granites? 292 00:16:54,880 --> 00:16:58,000 It simply seems to be this geochemical difference. 293 00:16:58,360 --> 00:17:00,320 It could be different starting compositions. 294 00:17:00,320 --> 00:17:02,720 You could explain this all by having different basils in the 295 00:17:02,720 --> 00:17:06,200 Ikean verses now and therefore making different platonic 296 00:17:06,200 --> 00:17:08,800 magmatic rocks. Or you could have different 297 00:17:08,800 --> 00:17:11,760 temperatures of melting which make these different protonic 298 00:17:11,760 --> 00:17:14,280 rocks. Or you could have different 299 00:17:14,359 --> 00:17:16,720 pressures of melting which use lutonic drugs. 300 00:17:16,720 --> 00:17:20,359 So this is also one of the reasons why our field has been 301 00:17:20,800 --> 00:17:24,440 tangled up for so long. But the fundamental difference 302 00:17:24,440 --> 00:17:27,319 is that modern day granite is very potassium rich, so you have 303 00:17:27,319 --> 00:17:31,600 a lot of K feldsparse, but TTGS it's much more sodium and 304 00:17:31,600 --> 00:17:34,400 calcium feldsparse instead. Yes, exactly. 305 00:17:34,400 --> 00:17:36,840 That is the main difference. Does that mean it's got more 306 00:17:36,840 --> 00:17:40,120 plasoclase? Precisely, yes, much more pledgy 307 00:17:40,120 --> 00:17:42,600 glaze versus K fell spot. It's a very simple switch. 308 00:17:43,000 --> 00:17:46,760 The other thing this could all be driven by is differences in 309 00:17:46,760 --> 00:17:50,040 fractional crystallization. So I've talked a lot about the 310 00:17:50,040 --> 00:17:52,800 partial melting processes because that's what I work on. 311 00:17:53,640 --> 00:17:57,720 But of course, once you make a magma, you can fractionally 312 00:17:57,720 --> 00:18:00,840 crystallize it, so you can form crystals which format fallout 313 00:18:00,840 --> 00:18:04,120 fall to the bottom of the magma chamber or magma system, and you 314 00:18:04,120 --> 00:18:06,000 can differentiate your melt that way. 315 00:18:06,480 --> 00:18:09,320 So that could also be one of the processes creating these 316 00:18:09,320 --> 00:18:13,840 differences between modern day granites and Archaean TTGS. 317 00:18:14,720 --> 00:18:16,280 There's a reason it's not solved yet. 318 00:18:18,960 --> 00:18:23,200 Today, about 30% of the Earth's surface is covered by 319 00:18:23,200 --> 00:18:26,560 continents, as I mentioned early on. 320 00:18:26,560 --> 00:18:31,080 I'm wondering, do we know if this kind of continental volume 321 00:18:31,080 --> 00:18:35,400 was formed in a burst early on in Earth history, for example 322 00:18:35,400 --> 00:18:40,200 when the TTGS started to form? Or did the amount of continental 323 00:18:40,200 --> 00:18:43,200 lithosphere accumulate steadily over geological time? 324 00:18:43,520 --> 00:18:46,280 It is really one of the things that remains the most unknown. 325 00:18:46,800 --> 00:18:49,680 And as I mentioned, there is like one big problem that 326 00:18:49,680 --> 00:18:52,240 hinders our understanding of this, and that's the 327 00:18:52,240 --> 00:18:56,440 preservation bias. So is what we have preserved now 328 00:18:56,560 --> 00:18:59,760 on Earth, when we look back at our 8% of the rocks that are key 329 00:18:59,760 --> 00:19:03,200 in does it actually represent what was on the surface at that 330 00:19:03,200 --> 00:19:07,040 time or does it represent one type of rock which was able to 331 00:19:07,040 --> 00:19:09,640 be preserved more easily? Or is it chance? 332 00:19:09,640 --> 00:19:12,560 Is it luck? Because we're always looking at 333 00:19:12,560 --> 00:19:15,880 this balance between creation of continental crust and 334 00:19:15,880 --> 00:19:17,480 destruction of continental crust. 335 00:19:17,960 --> 00:19:21,120 And those two things don't have to be the same throughout time. 336 00:19:21,120 --> 00:19:24,520 They can change. And of course, because some of 337 00:19:24,520 --> 00:19:28,320 this cross has been destroyed, it makes it very hard to say 338 00:19:28,360 --> 00:19:31,080 something about about what we've actually lost from the 339 00:19:31,080 --> 00:19:37,200 geological record. I would say that what we see in 340 00:19:37,200 --> 00:19:42,080 the geological record is impacted by a preservation bias. 341 00:19:42,080 --> 00:19:45,360 It does not represent the world at that time. 342 00:19:45,560 --> 00:19:48,320 So we have to really take this into account when we're trying 343 00:19:48,320 --> 00:19:52,000 to understand our crustal growth models, as you say, which is the 344 00:19:52,000 --> 00:19:54,680 total volume of continental crust on the air. 345 00:19:55,400 --> 00:19:58,440 I mentioned that you're interested in the possible role 346 00:19:58,440 --> 00:20:03,400 of hydrogen in powering the earliest forms of life. 347 00:20:04,040 --> 00:20:07,480 First of all, can life really be fueled by hydrogen? 348 00:20:07,480 --> 00:20:09,200 Are we talking about molecular hydrogen? 349 00:20:09,720 --> 00:20:13,240 And presumably this was well before the Earth's atmosphere 350 00:20:13,240 --> 00:20:16,080 became oxygenated. That's exactly right. 351 00:20:16,080 --> 00:20:18,880 So we're talking about molecular hydrogen or H2. 352 00:20:19,560 --> 00:20:23,440 And yes, this is well before the atmosphere was oxygenated. 353 00:20:23,440 --> 00:20:28,720 So the great Oxygen Asian event was around 2.4 to 2.1 billion 354 00:20:28,720 --> 00:20:32,640 years ago, but we seem to have had evidence of life well before 355 00:20:32,640 --> 00:20:36,080 that. So this is quite a fun thing 356 00:20:36,080 --> 00:20:41,680 because these types of organisms are called Archaea and some of 357 00:20:41,680 --> 00:20:43,840 them are hydrogen, some of them is methane. 358 00:20:43,840 --> 00:20:46,760 They use all sorts of different compounds to get their energy. 359 00:20:46,920 --> 00:20:49,520 And these particular type of methanogens, they're called, 360 00:20:49,520 --> 00:20:54,080 they use molecular hydrogen, H2 and CO2 to form methane. 361 00:20:54,160 --> 00:20:55,720 And this is their main energy source. 362 00:20:56,920 --> 00:20:59,080 And incredibly, they're still around today. 363 00:20:59,080 --> 00:21:01,960 So we believe that they evolved in the Archaean, but we can 364 00:21:01,960 --> 00:21:04,080 still find them today. They're in our guts, they're in 365 00:21:04,080 --> 00:21:07,120 our mouths, and they're living in the Atlantic Ocean in 366 00:21:07,120 --> 00:21:09,880 hydrothermal vents where they get hydrogen from rocks. 367 00:21:09,880 --> 00:21:13,320 So they seem to be quite prolific in the world. 368 00:21:14,080 --> 00:21:17,480 So, but the key problem was in the Archaean for the Great 369 00:21:17,480 --> 00:21:21,120 Oxygenation event, the atmosphere was really primarily 370 00:21:21,120 --> 00:21:25,240 composed of nitrogen, carbon dioxide and perhaps methane or 371 00:21:25,240 --> 00:21:27,640 ammonia. So this meant that the first 372 00:21:27,640 --> 00:21:32,200 life forms had to be anaerobic. They couldn't use oxygen as an 373 00:21:32,200 --> 00:21:37,640 energy source to create energy. So this group of Archaea, they 374 00:21:37,920 --> 00:21:41,400 most likely evolved in the oceans or in shallow lakes in 375 00:21:41,400 --> 00:21:44,400 the Archaean where they were using this molecular hydrogen. 376 00:21:45,000 --> 00:21:50,400 And how would the hydrogen be produced in these Archaean 377 00:21:50,640 --> 00:21:54,120 oceans or lakes? Yeah, it's a fantastic question 378 00:21:54,120 --> 00:21:56,800 because we come back to these wonderful commodities I 379 00:21:56,800 --> 00:21:59,560 mentioned earlier, these highly magnesium lavas. 380 00:22:00,240 --> 00:22:04,800 So quite incredibly, the exact same reaction which tracks water 381 00:22:04,800 --> 00:22:08,600 in these rocks. This hydration reaction is also 382 00:22:08,600 --> 00:22:13,680 actually an oxidizing reaction. So during this hydration, the 383 00:22:13,680 --> 00:22:16,760 iron 2 plus in the rock is converted to iron 3 plus. 384 00:22:17,400 --> 00:22:20,880 And because of the unique chemistry of these rocks, this 385 00:22:20,880 --> 00:22:24,920 in turn dissociates the water so it traps oxygen in the rocks and 386 00:22:24,920 --> 00:22:28,800 releases hydrogen. And it's quite amazing. 387 00:22:28,800 --> 00:22:31,480 It's all kind of the same chemical reaction, doing all of 388 00:22:31,480 --> 00:22:34,640 these things, hydrating the rock, oxidizing the rock and 389 00:22:34,640 --> 00:22:38,720 releasing the hydrogen. And because we think the oceans 390 00:22:38,720 --> 00:22:41,800 then also had quite a lot of CO2 in them, we see evidence for 391 00:22:41,800 --> 00:22:45,040 that in the sedimentary record. So these Archaea would have had 392 00:22:45,040 --> 00:22:49,160 the CO2, the hydrogen to combine to make methane and survive. 393 00:22:50,360 --> 00:22:53,600 And the intriguing thing is that this could also be a possible 394 00:22:53,600 --> 00:22:56,960 way for the evolution of life on other planets where there's not 395 00:22:57,080 --> 00:23:00,160 any oxygen, but there might be water available. 396 00:23:00,160 --> 00:23:02,640 And also these oxidizing reactions taking place. 397 00:23:03,400 --> 00:23:07,040 We can also go one step further, which is why I kind of mentioned 398 00:23:07,040 --> 00:23:10,600 before is you brought up interestingly this kind of dying 399 00:23:10,600 --> 00:23:14,080 off of the commodity eye about 2.5 to 2 billion years ago, 400 00:23:15,000 --> 00:23:17,160 which actually directly correlates with the great 401 00:23:17,160 --> 00:23:20,400 oxygenation event. So this big switch in how the 402 00:23:20,400 --> 00:23:23,440 Earth, the solid Earth and also the atmosphere seem to work. 403 00:23:24,480 --> 00:23:27,200 And there's been a few studies that have actually suggested 404 00:23:27,440 --> 00:23:31,320 that these commodities produce so much hydrogen in the oceans 405 00:23:31,520 --> 00:23:35,120 that are acted as a drawdown for oxygen from the atmosphere to 406 00:23:35,120 --> 00:23:39,080 recombine to make H2O water. And that actually the 407 00:23:39,080 --> 00:23:41,960 commodities, the Earth cooling and the commodities starting to 408 00:23:41,960 --> 00:23:44,440 be erupted less and less. Therefore, producing less and 409 00:23:44,440 --> 00:23:48,000 less hydrogen actually is what allowed the oxygen levels in the 410 00:23:48,000 --> 00:23:51,480 atmosphere to finally take off, leading to the great Oxygenation 411 00:23:51,480 --> 00:23:54,040 event. What are you working on at the 412 00:23:54,040 --> 00:23:56,800 moment? So at the moment I'm finishing 413 00:23:56,800 --> 00:24:00,000 up my work looking at the interactions between commodities 414 00:24:00,000 --> 00:24:02,800 and the ocean and the atmosphere to understand some of the 415 00:24:02,800 --> 00:24:05,720 chemical cycling that may have been taking place at that time. 416 00:24:06,480 --> 00:24:09,840 And I'm starting to look more towards the TTG production. 417 00:24:09,840 --> 00:24:14,360 So creating models to try to understand exactly how these 418 00:24:14,360 --> 00:24:16,960 basalts may have melted and to constrain what we were 419 00:24:16,960 --> 00:24:20,360 discussing before. Really, what were the greatest 420 00:24:20,360 --> 00:24:22,680 effects? Temperature, pressure, water 421 00:24:22,680 --> 00:24:24,600 availability, starting composition? 422 00:24:24,640 --> 00:24:28,400 How did they all play a role in creating the TTGS? 423 00:24:29,240 --> 00:24:35,640 Is the existence of the TTGS viewed as a puzzle, or do we 424 00:24:36,000 --> 00:24:38,760 understand enough not to be surprised if they're there, but 425 00:24:38,760 --> 00:24:40,560 you're trying to flesh out the details? 426 00:24:40,800 --> 00:24:42,920 I would like to flesh out the details. 427 00:24:42,920 --> 00:24:45,040 The details in this point matter. 428 00:24:45,560 --> 00:24:49,000 It seems like there is a non unique solution to creating 429 00:24:49,000 --> 00:24:52,360 TTGSI think I mentioned before. And there's also a non unique 430 00:24:52,360 --> 00:24:56,360 solution from going from these TTGS to the more potassium rich 431 00:24:56,360 --> 00:24:59,360 rocks we have in the more recent geological record. 432 00:25:00,200 --> 00:25:03,880 So the focus of my next study is to work out what actually are 433 00:25:03,880 --> 00:25:08,240 the most important factors. And also a lot of the studies 434 00:25:08,240 --> 00:25:11,120 have done very broad scale studies, but I'm hoping to go 435 00:25:11,120 --> 00:25:14,120 more into depth looking at very particular case studies and some 436 00:25:14,120 --> 00:25:17,120 of these Arcan terrains to try to wiggle out. 437 00:25:17,120 --> 00:25:19,480 What are the most important parts of this recipe? 438 00:25:20,840 --> 00:25:22,800 Renee Tamblyn, thank you very much. 439 00:25:23,080 --> 00:25:24,840 Thank you, Oliver, it's been very fun. 440 00:25:24,920 --> 00:25:28,800 I enjoyed it a lot. 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