1 00:00:04,600 --> 00:00:07,500 This is geology B with all of us trampled. 2 00:00:08,800 --> 00:00:13,500 In 1788, James Hutton, spotted a spectacular and Conformity at 3 00:00:13,500 --> 00:00:16,100 siccar point on the east coast of Scotland. 4 00:00:16,900 --> 00:00:20,300 He was the first to understand that although to sedimentary 5 00:00:20,300 --> 00:00:24,100 rock types were in contact with each other, they're the boundary 6 00:00:24,100 --> 00:00:27,400 between them represented a gap in the geological record. 7 00:00:28,300 --> 00:00:32,700 The Rocks below which contained Marine fossils were deposited in 8 00:00:32,700 --> 00:00:35,000 a deep ocean during the silurian. 9 00:00:35,700 --> 00:00:40,000 But only after these rocks had been folded uplifted and eroded 10 00:00:40,200 --> 00:00:43,700 where the overlying Rocks deposited in a devonian desert. 11 00:00:44,800 --> 00:00:49,000 In this very clear-cut case, 80 million years are missing from 12 00:00:49,000 --> 00:00:52,800 the record but the gaps in the sedimentary record are not 13 00:00:52,800 --> 00:00:57,000 always so obvious. Indeed sedimentary sequences 14 00:00:57,000 --> 00:00:59,600 that look continuous and complete can be quite the 15 00:00:59,600 --> 00:01:02,700 opposite. Clearly if we want to read this 16 00:01:02,700 --> 00:01:06,200 element illogical record to make accurate inferences about the 17 00:01:06,200 --> 00:01:09,800 past, we need to recognize and interpret the gaps in the 18 00:01:09,800 --> 00:01:13,000 record, as well as the parts of the record that survived to the 19 00:01:13,000 --> 00:01:17,200 present day. How do depositional mechanisms 20 00:01:17,200 --> 00:01:22,400 and subsequent events alter or destroy parts of the record more 21 00:01:22,400 --> 00:01:25,400 fundamentally? How can we tell that the record 22 00:01:25,400 --> 00:01:28,600 is good enough to make any solid inferences about the geological 23 00:01:28,600 --> 00:01:33,600 past Bruce level addresses. These questions by combining 24 00:01:33,600 --> 00:01:37,100 field work with systemic analysis based on what we know 25 00:01:37,100 --> 00:01:40,400 about contemporary depositional an erosional processes. 26 00:01:41,400 --> 00:01:44,500 Armed with an understanding of the preservation all biases that 27 00:01:44,500 --> 00:01:47,700 can apply. He has been re-examining, some 28 00:01:47,700 --> 00:01:51,200 widely accepted interpretations of the sedimentary record. 29 00:01:52,100 --> 00:01:55,200 For example, by analyzing sequences of glacially 30 00:01:55,200 --> 00:01:57,600 deposited, rocks, in South West, Scotland. 31 00:01:58,000 --> 00:02:02,000 He has shown that contrary to the widely held snowball Earth. 32 00:02:02,000 --> 00:02:05,600 Hypothesis parts of the earth were not covered by ice. 33 00:02:05,900 --> 00:02:08,100 At least during the earlier of the two snowball. 34 00:02:08,100 --> 00:02:12,700 Glaciations Bruce. Oil is a visiting professor in 35 00:02:12,700 --> 00:02:15,900 the department of Earth Sciences at the University of Oxford. 36 00:02:16,500 --> 00:02:19,600 Previously, he was Chief scientist for Geology at Royal 37 00:02:19,600 --> 00:02:22,000 Dutch. Shell Bruce level. 38 00:02:22,000 --> 00:02:24,500 Welcome to geology, B, pleased to be here. 39 00:02:24,500 --> 00:02:27,100 Oliver, let's start with the fundamental question. 40 00:02:27,100 --> 00:02:30,900 I just raised, how do we know that the sedimentary record is 41 00:02:30,900 --> 00:02:34,200 complete enough to make solid inferences about the past? 42 00:02:34,500 --> 00:02:37,400 This is a very old question, it goes back to Darwin or perhaps 43 00:02:37,400 --> 00:02:39,700 even earlier in the Origin of Species. 44 00:02:39,700 --> 00:02:44,300 He wrote, I Could the geological record as a history of the world 45 00:02:44,300 --> 00:02:49,600 imperfectly, kept and written, in a changing dialect of this 46 00:02:49,600 --> 00:02:53,500 history, we possess the last volume alone relating to only 47 00:02:53,500 --> 00:02:58,300 two or three countries of this. Volume only here and there a 48 00:02:58,300 --> 00:03:03,000 short chapter has been preserved and of each page, only here and 49 00:03:03,000 --> 00:03:08,700 there a few lines. So Darwin's problem was that he 50 00:03:08,700 --> 00:03:12,800 was being challenged to produce the intermediate forms which 51 00:03:12,800 --> 00:03:16,200 document the evolution of one species into another by natural 52 00:03:16,200 --> 00:03:21,900 selection and his defense to not being able to produce that many 53 00:03:21,900 --> 00:03:24,800 examples of intermediate forms, was that the record was 54 00:03:24,900 --> 00:03:26,600 imperfectly kept as you wrote here? 55 00:03:27,100 --> 00:03:30,300 So it's a fundamental question and I think the answer is we 56 00:03:30,300 --> 00:03:32,000 know that the record is incomplete. 57 00:03:32,800 --> 00:03:35,700 So your question is it complete enough? 58 00:03:36,400 --> 00:03:39,400 It also very well phrased. Because whether or not, it's 59 00:03:39,400 --> 00:03:41,500 complete. Depends upon the question that 60 00:03:41,500 --> 00:03:44,600 you're asking. So if we look at Darwin's quote 61 00:03:44,600 --> 00:03:47,500 and we change his metaphor a little bit, if I were to keep a 62 00:03:47,508 --> 00:03:51,000 diary, and I want to miss the occasional entry that might be 63 00:03:51,000 --> 00:03:53,300 sufficient to give you an idea of what I was doing for the 64 00:03:53,300 --> 00:03:55,400 year. If you just wanted to know, what 65 00:03:55,400 --> 00:03:57,800 is Bruce, get up to, when did he go on holiday? 66 00:03:57,800 --> 00:03:59,400 How much time does he spend working? 67 00:04:00,000 --> 00:04:03,200 But if you wanted to know, what did he eat every day, then the 68 00:04:03,208 --> 00:04:05,600 entries wouldn't be complete enough to answer that question. 69 00:04:06,400 --> 00:04:08,400 And they might be incomplete in different ways. 70 00:04:08,400 --> 00:04:11,100 So it might be that I don't write down on Friday. 71 00:04:11,100 --> 00:04:13,900 Evenings what I'm doing because they don't get around to writing 72 00:04:13,900 --> 00:04:16,200 my diary. So you'd have a systematic error 73 00:04:16,200 --> 00:04:19,600 or bias in the record that Friday's won't preserved. 74 00:04:20,600 --> 00:04:23,800 So data has been collected or sedimentary record to ask 75 00:04:23,800 --> 00:04:26,500 exactly this question. This was done by a guy called 76 00:04:26,500 --> 00:04:30,100 Pete, Sadler in the early 80s and he made an extremely 77 00:04:30,100 --> 00:04:33,600 revealing plot which has on the vertical axis, the accumulation 78 00:04:33,600 --> 00:04:37,000 rate of sediments and on the Horizontal axis. 79 00:04:37,000 --> 00:04:40,300 It's got the averaging time over, which the rate has been 80 00:04:40,300 --> 00:04:43,600 measured. So if I measure a rate over the 81 00:04:43,600 --> 00:04:46,500 duration of a flood that would be entered as maybe a week or 82 00:04:46,500 --> 00:04:50,700 perhaps a month on a big river when it was in Spate and we're 83 00:04:50,700 --> 00:04:54,300 how much sediment was deposited during that event at The Other 84 00:04:54,300 --> 00:04:56,700 Extreme? I look at sedimentary basins and 85 00:04:56,700 --> 00:05:01,600 I say, what is the accumulation rate of sediment in say the 86 00:05:01,600 --> 00:05:05,500 Wessex Basin of Southern England and what you find on that plot 87 00:05:05,500 --> 00:05:10,300 is A linear inverse relationship between the accumulation rate 88 00:05:10,600 --> 00:05:12,500 and the time over which its measured. 89 00:05:13,100 --> 00:05:17,000 So my flood, deposit is accumulated relatively fast over 90 00:05:17,000 --> 00:05:21,800 a short period of time, maybe a meter or even 2 m over a month 91 00:05:22,400 --> 00:05:25,900 whereas in the sedimentary Basin, I'm talking about, mm a 92 00:05:25,900 --> 00:05:30,900 year meters over thousands of years, maybe even tens of 93 00:05:30,907 --> 00:05:32,600 thousands of years in some cases. 94 00:05:32,900 --> 00:05:36,000 And what it says is that there are gaps at alterations in the 95 00:05:36,100 --> 00:05:40,300 God and those gaps accumulate as you increase the averaging time 96 00:05:40,300 --> 00:05:42,400 and therefore become more important. 97 00:05:42,400 --> 00:05:45,000 So the record does have the fractal gaps that Darwin 98 00:05:45,000 --> 00:05:50,400 postulated back in 1859 are we sure that we always do know when 99 00:05:50,400 --> 00:05:53,000 something is missing might something look complete when in 100 00:05:53,000 --> 00:05:57,400 fact perhaps it isn't absolutely it often looks complete. 101 00:05:57,400 --> 00:06:00,300 When in fact, it isn't and that's a mistake, I've made many 102 00:06:00,300 --> 00:06:04,600 times in my career typically when you look at core data, 103 00:06:04,600 --> 00:06:08,800 extracted from the subsurface, Yes, it's a vertical column and 104 00:06:08,900 --> 00:06:11,600 maybe only four inches, wide, 10, cm wide. 105 00:06:12,200 --> 00:06:15,500 And I'm always surprised when I get the paleontological data 106 00:06:16,000 --> 00:06:18,800 which tells me that there's time missing, there's always more 107 00:06:18,800 --> 00:06:21,700 missing than you think mind. The gap is a very good slogan 108 00:06:21,700 --> 00:06:23,800 for a sedimentology. Just what? 109 00:06:23,800 --> 00:06:26,900 Exactly would we like to learn about the past? 110 00:06:27,200 --> 00:06:29,800 If only, we could correctly interpret, the sedimentary 111 00:06:29,800 --> 00:06:34,300 record, there are two main ways. We use the sedimentary record to 112 00:06:34,300 --> 00:06:38,000 extract information, The first as a Time series of information 113 00:06:38,000 --> 00:06:40,800 as Darwin would have liked to, he would have liked to have had 114 00:06:40,900 --> 00:06:44,100 a continuous time series. All be it put together from bits 115 00:06:44,100 --> 00:06:46,000 of the record, in different parts of the world to make a 116 00:06:46,008 --> 00:06:49,600 composite time series but a continuous time series from the 117 00:06:49,600 --> 00:06:53,000 origin of life to the present day in the modern day. 118 00:06:53,000 --> 00:06:56,800 With the Fantastic advances in geochemistry particularly 119 00:06:56,800 --> 00:07:00,600 isotope geochemistry people that are wanting to put together, 120 00:07:00,800 --> 00:07:04,000 continuous complete records of the evolution of the Earth's 121 00:07:04,000 --> 00:07:05,900 system. So ocean chemistry. 122 00:07:06,000 --> 00:07:09,300 Chemistry, ocean temperature, any information about the 123 00:07:09,300 --> 00:07:11,800 atmosphere, which you can get from, for instance, plant 124 00:07:11,800 --> 00:07:15,600 remains or even trapped air in Antarctica, and in the ice 125 00:07:15,600 --> 00:07:18,000 cores. So, continuous, time series of 126 00:07:18,000 --> 00:07:23,900 data and some examples of those might be the Paleo climate 127 00:07:24,000 --> 00:07:27,800 interpolating time between points of control, where we have 128 00:07:27,800 --> 00:07:32,300 radiometric ages, understanding the fossil record and how it 129 00:07:32,300 --> 00:07:35,900 evolved and understanding events in geological history. 130 00:07:36,100 --> 00:07:37,500 I'm putting them in their time, sequel. 131 00:07:37,500 --> 00:07:39,300 So those could be major climate shifts. 132 00:07:39,300 --> 00:07:43,100 That could be major storms. They could be sea level changes 133 00:07:43,400 --> 00:07:47,300 could be meteorite impacts various scales of occurrence 134 00:07:47,300 --> 00:07:50,300 from almost daily weekly, monthly events which are making 135 00:07:50,300 --> 00:07:52,400 up geological record by putting deposits down. 136 00:07:52,400 --> 00:07:56,500 In a particular way to these spasmodic episodic revolutionary 137 00:07:56,500 --> 00:08:00,200 events and then the second way in which we use the sedimentary 138 00:08:00,200 --> 00:08:04,800 record is to predict essentially to geometry of sedimentary 139 00:08:04,800 --> 00:08:07,100 deposits. Because we want to use them to 140 00:08:07,100 --> 00:08:10,200 extract things or to store things or to build things on. 141 00:08:11,100 --> 00:08:13,300 So, in that case, we want to understand the three dimensional 142 00:08:13,300 --> 00:08:15,200 geometry. And in order to understand the 143 00:08:15,200 --> 00:08:19,700 three-dimensional geometry, the obvious route to use is the fact 144 00:08:19,700 --> 00:08:23,300 that all sediments are deposited in an environment and that 145 00:08:23,300 --> 00:08:25,000 environment. If you'd have had a sort of 146 00:08:25,000 --> 00:08:28,300 paleo satellite back, when the Rocks were being formed, would 147 00:08:28,300 --> 00:08:31,700 have looked like some sort of map of channels and bars and 148 00:08:31,700 --> 00:08:34,700 beaches and coastlines and tidal inlets. 149 00:08:34,700 --> 00:08:40,100 And Our fans, etc, etc. And if we can reconstruct the T 150 00:08:40,100 --> 00:08:43,400 position of environment, then we can predict to a degree the 151 00:08:43,400 --> 00:08:45,500 three-dimensional geometry of the rock units. 152 00:08:46,000 --> 00:08:49,400 So those are the kind of two main classes of use. 153 00:08:49,400 --> 00:08:51,300 I'd say of the sedimentary archive. 154 00:08:51,700 --> 00:08:56,100 Okay, let's talk about the preservation, 'l bias. 155 00:08:56,100 --> 00:08:58,900 If you like, in the record in the context of each of these 156 00:08:58,900 --> 00:09:02,400 aspects. So first of all, what kinds of 157 00:09:02,400 --> 00:09:06,000 bias would tend to confound our understanding of the Palio So 158 00:09:06,000 --> 00:09:09,100 climate in order to understand the Paleo climate, we need to 159 00:09:09,100 --> 00:09:11,400 make a measurement which response to temperature, so 160 00:09:11,400 --> 00:09:14,400 called proxies can be a wide variety of things. 161 00:09:14,400 --> 00:09:18,800 So for example, people look at the temperature of formation of 162 00:09:18,800 --> 00:09:21,900 soil, nodules using carbon and oxygen Isotopes. 163 00:09:21,900 --> 00:09:24,600 You can say something about the temperature, which is soil 164 00:09:24,600 --> 00:09:27,400 experienced. Alternatively, you might look at 165 00:09:27,400 --> 00:09:31,300 changes in the rate of phytoplankton production or you 166 00:09:31,300 --> 00:09:33,600 could measure the surface temperature of foraminifera 167 00:09:33,600 --> 00:09:37,100 living in the surface of the And you might even be able to 168 00:09:37,100 --> 00:09:39,800 compare that with the temperature of foraminifera, 169 00:09:39,800 --> 00:09:42,900 living on the bottom of the ocean, so you could get the 170 00:09:42,900 --> 00:09:45,000 temperature gradient in the water column. 171 00:09:45,500 --> 00:09:48,500 So you want to take a series of samples, which you can analyze 172 00:09:48,500 --> 00:09:51,000 in a lab and extract some temperature data, typically 173 00:09:51,000 --> 00:09:55,100 using an isotopic proxy. Now, in order to do that, you 174 00:09:55,100 --> 00:09:57,400 need to make a series of assumptions in order to have 175 00:09:57,400 --> 00:09:59,300 that. As a Time series of data, the 176 00:09:59,300 --> 00:10:03,200 first is that the record is indeed continuous at the scale, 177 00:10:03,200 --> 00:10:06,900 at which you wish to sample it. So, So if you're want to 178 00:10:06,900 --> 00:10:11,000 reconstruct this over the time scale of 25,000 years or so, 179 00:10:11,800 --> 00:10:14,900 then you would need on that time scale. 180 00:10:15,000 --> 00:10:18,800 They're not to be gaps in the record so you could go to 181 00:10:18,800 --> 00:10:22,500 sedimentary sequences. We're on the time scale of a few 182 00:10:22,500 --> 00:10:24,600 thousands of years, record is continuous. 183 00:10:24,600 --> 00:10:28,800 And the obvious one to go to is a deep water deposit because 184 00:10:28,800 --> 00:10:31,700 they're the preservation will bias is very low. 185 00:10:32,100 --> 00:10:34,800 Almost everything that falls down to the bottom of the ocean 186 00:10:34,900 --> 00:10:37,700 gets deposited. To provided it doesn't get eaten 187 00:10:38,400 --> 00:10:40,400 or in the deep ocean gets dissolved. 188 00:10:40,900 --> 00:10:42,700 So they're your problem is less great. 189 00:10:42,700 --> 00:10:45,100 If you like you have more chance of being successful, the 190 00:10:45,100 --> 00:10:48,300 preservation biases, due to burrowing organisms coming 191 00:10:48,300 --> 00:10:51,300 across my microorganism and eating it before, it has a 192 00:10:51,308 --> 00:10:53,900 chance to be preserved or eating all of them from a particular 193 00:10:53,900 --> 00:10:55,700 time period before they have a chance to preserve. 194 00:10:55,900 --> 00:10:59,700 If we come back to my soil nodule in a Fluval sequence, the 195 00:10:59,700 --> 00:11:04,600 situation is entirely different because the soil model is 196 00:11:04,600 --> 00:11:07,400 forming. Outside the channel of a river. 197 00:11:08,500 --> 00:11:11,300 Now, that channels of rivers tend to migrate they don't stay 198 00:11:11,300 --> 00:11:13,600 in one place forever, they migrate sideways. 199 00:11:14,000 --> 00:11:19,200 And therefore, they erode, soil profiles and particularly those, 200 00:11:19,200 --> 00:11:21,700 which are closer to the level of the river are going to be 201 00:11:21,700 --> 00:11:23,200 destroyed. And those are going to be 202 00:11:23,200 --> 00:11:27,700 preserved would be the ones for example, on Terraces, which are 203 00:11:27,700 --> 00:11:30,800 at a higher level away from the river itself. 204 00:11:31,100 --> 00:11:34,100 So you'd end up with a record, which would be variably 205 00:11:34,100 --> 00:11:38,200 incomplete and it might even be difficult to reconstitute. 206 00:11:38,300 --> 00:11:40,800 For instance to Terrace deposits will be topographically higher 207 00:11:40,800 --> 00:11:42,700 than the river channel. So they would not be 208 00:11:42,700 --> 00:11:45,500 contemporaneous with that particular River channel. 209 00:11:45,500 --> 00:11:47,600 So, you end up with a problem of sorting out the age 210 00:11:47,600 --> 00:11:50,100 relationships, if your variable sections in which you've 211 00:11:50,100 --> 00:11:54,000 measured these things and you also end up with the record that 212 00:11:54,000 --> 00:11:57,700 quite a lot of the sequence may be destroyed depending on how 213 00:11:57,700 --> 00:12:00,400 far the river eats into the flood Basin. 214 00:12:01,100 --> 00:12:04,500 So those are two contrasting situations in general. 215 00:12:04,500 --> 00:12:08,100 Preservation bias is very strongly controlled by erosion. 216 00:12:08,200 --> 00:12:12,000 Ian, the most dangerous thing for a sediment is after, it's 217 00:12:12,000 --> 00:12:15,300 been deposited is to be re eroded by the next River flood, 218 00:12:15,300 --> 00:12:18,800 or by the next storm. And it's only when it subsided, 219 00:12:18,800 --> 00:12:22,000 a certain increment out of Harm's Way. 220 00:12:22,100 --> 00:12:25,100 So Below the depth of the migrating River Channel or below 221 00:12:25,100 --> 00:12:27,900 the erosional capacity of the subsequent storm, it's been 222 00:12:27,900 --> 00:12:29,600 buried. Sufficiently deeply that it's 223 00:12:29,600 --> 00:12:33,400 definitively preserved. So sediments after d position, 224 00:12:33,400 --> 00:12:36,200 they're kind of tentatively preserved. 225 00:12:36,800 --> 00:12:42,300 And they may spend 10 20 30 40 50 hundred thousand years in 226 00:12:42,300 --> 00:12:45,700 tentative preservation and it's only subsidence. 227 00:12:45,800 --> 00:12:49,700 Which definitively preserves them by removing them from the 228 00:12:49,700 --> 00:12:53,300 zone of active surface, currents and waves, Etc. 229 00:12:53,500 --> 00:12:57,300 You refer to connecting the two different time scales that we 230 00:12:57,300 --> 00:13:01,800 have and indeed a major undertaking over the past 231 00:13:01,800 --> 00:13:05,600 decades has been the marrying of the stratigraphic time scale, 232 00:13:06,200 --> 00:13:10,100 which is So on the sedimentary record with the absolute time 233 00:13:10,100 --> 00:13:13,400 scale, which is determined from radiometric, dating? 234 00:13:14,300 --> 00:13:17,200 Can you quickly remind us how that is done? 235 00:13:17,600 --> 00:13:20,000 Yeah. Reliable, radiometric dates from 236 00:13:20,000 --> 00:13:22,900 sedimentary rocks, are really difficult because you basically 237 00:13:22,900 --> 00:13:26,600 need a high temperature mineral to set the isotopic clock 238 00:13:26,600 --> 00:13:30,000 running and preserve the daughter products, and the best 239 00:13:30,000 --> 00:13:31,900 mineral that we have. The middle of choice is clearly 240 00:13:31,900 --> 00:13:35,100 Zircon with uranium-lead dating because it has a couple of 241 00:13:35,100 --> 00:13:38,100 isotopic systems when you can. Do internal, consistency, checks 242 00:13:38,600 --> 00:13:40,500 and those? Come from, felsic, volcanics. 243 00:13:41,100 --> 00:13:44,400 And so what you need is to find volcanic Tufts into bed with 244 00:13:44,400 --> 00:13:47,800 sediments and ideally. Those sediments should be fossil 245 00:13:47,800 --> 00:13:50,800 bearing and then you can calibrate, the fossil record 246 00:13:51,200 --> 00:13:54,400 with the absolute age that you get from those radiometric dates 247 00:13:55,000 --> 00:13:58,100 as an example. The lower Jurassic blue Liars of 248 00:13:58,100 --> 00:14:01,200 Lyme Regis, which many people know, the radiometric dates, 249 00:14:01,200 --> 00:14:04,000 which date part of that succession come from Peru. 250 00:14:04,100 --> 00:14:07,800 Because that's where no Jurassic have It's a nicely into bedded 251 00:14:07,800 --> 00:14:09,900 with well dated Tufts in the Andes. 252 00:14:10,400 --> 00:14:13,300 So what that means is that you've got a bunch of ammonites 253 00:14:13,300 --> 00:14:15,500 in Peru. Unfortunately, the same evidence 254 00:14:15,500 --> 00:14:18,400 didn't live in Dorset, the different biogeographic 255 00:14:18,400 --> 00:14:22,000 provinces. So you need to connect the two 256 00:14:22,400 --> 00:14:26,000 groups of ammonites and their evolution re records across two 257 00:14:26,000 --> 00:14:30,000 different oceans and you do that by finding intermediate fossil 258 00:14:30,000 --> 00:14:34,100 groups with which both can be interbedded or via you can find 259 00:14:34,100 --> 00:14:36,200 a connection. So you might find pollen or you 260 00:14:36,200 --> 00:14:40,400 might Find foraminifera again or calcareous Nano fossils, 261 00:14:40,400 --> 00:14:41,300 whatever. It might be. 262 00:14:41,700 --> 00:14:44,500 That can connect those two formal provinces together and 263 00:14:44,500 --> 00:14:47,700 then you end up with inferred radiometric ages for Lyme Regis. 264 00:14:48,100 --> 00:14:50,900 Now, you still only got a few ages and quite a lot of rock. 265 00:14:51,200 --> 00:14:53,800 So if you want to make a Time series of paleo climate data, 266 00:14:53,800 --> 00:14:57,100 for the lower, Jurassic in the UK, you have to interpolate 267 00:14:57,100 --> 00:15:01,300 between the radiometric points and method of choice for that is 268 00:15:01,300 --> 00:15:05,000 to use the rhythms, which come from orbital cyclicity. 269 00:15:05,000 --> 00:15:08,100 So you have the change in the Eccentricity the change in 270 00:15:08,600 --> 00:15:11,400 frequency of the orbit and the change in precession of the 271 00:15:11,400 --> 00:15:15,900 Earth's axis just to explain the Earth orbital eccentricity is 272 00:15:15,900 --> 00:15:19,000 the amount by which the Earth's orbit around the Sun deviates 273 00:15:19,000 --> 00:15:22,900 from A Perfect Circle which varies with about 100,000 year 274 00:15:22,900 --> 00:15:26,300 periodicity. The obliquity is the tilt of the 275 00:15:26,300 --> 00:15:29,000 Earth's axis of rotation with respect to the plane of the 276 00:15:29,000 --> 00:15:32,900 Earth's orbit around the Sun and that varies with a periodicity 277 00:15:32,900 --> 00:15:37,500 of about 41,000 years and the procession Is the wobble of the 278 00:15:37,500 --> 00:15:40,700 Earth's axis like that of a spinning top which has about a 279 00:15:40,708 --> 00:15:43,100 26,000-year period. Yeah. 280 00:15:43,200 --> 00:15:47,400 And these combined give you a series of ratios effectively 281 00:15:47,400 --> 00:15:50,700 between those rhythms which you can find back in the geological 282 00:15:50,700 --> 00:15:53,600 record as expressed by differences in the sedimentation 283 00:15:53,700 --> 00:15:56,400 if you're lucky. So if for instance, you've got 284 00:15:56,400 --> 00:15:59,500 difference in the rate of production of calcareous 285 00:15:59,600 --> 00:16:02,700 Plankton that would Express itself in a liveliness of The 286 00:16:02,700 --> 00:16:06,100 Rock and you can measure that line - directly or indirectly 287 00:16:06,100 --> 00:16:10,200 and Up with extracting these rhythms and then you can 288 00:16:10,200 --> 00:16:13,800 so-called astronomically tune the time scale. 289 00:16:13,800 --> 00:16:16,800 So you can count The rhythms in between your radiometric dates 290 00:16:16,800 --> 00:16:21,600 and you can infer a an age between the radiometric age 291 00:16:21,600 --> 00:16:23,600 points. And in the last edition of the 292 00:16:23,600 --> 00:16:27,100 geological time scale, there's been a major major attempt to 293 00:16:27,100 --> 00:16:30,300 astronomically tune large parts of the stratigraphic record and 294 00:16:30,300 --> 00:16:32,800 this is actually a major undertaking but it does require 295 00:16:32,800 --> 00:16:36,000 huge be able to find composite sections in the record which are 296 00:16:36,500 --> 00:16:41,600 eat and continuous and it can be very confusing of sedimentation 297 00:16:41,600 --> 00:16:44,300 rate changes because the Rhythm that you're measuring is in 298 00:16:44,300 --> 00:16:48,500 thickness, not in time and you have to transform it from 299 00:16:48,500 --> 00:16:51,600 thickness to time. Using the argument that you've 300 00:16:51,600 --> 00:16:54,600 got a complete Rhythm. So it is quite an involved 301 00:16:54,600 --> 00:16:58,800 exercise and it sets very high requirements on completeness and 302 00:16:58,800 --> 00:17:02,000 continuity of the record and also steadiness of D position. 303 00:17:02,800 --> 00:17:05,700 If now, there is something that's interfere with the 304 00:17:05,700 --> 00:17:08,900 sedimentary record, Occurred in those intervening bands, between 305 00:17:08,900 --> 00:17:12,400 the radiometric dated bands, does it always show up and can 306 00:17:12,400 --> 00:17:15,800 we then account for that? It's a real detective game that 307 00:17:15,800 --> 00:17:17,599 a night. So nations in this case can give 308 00:17:17,599 --> 00:17:19,500 you a clue as to where things are missing. 309 00:17:20,000 --> 00:17:21,500 But there are some beautiful examples. 310 00:17:21,500 --> 00:17:24,900 If you compare this lower Jurassic in Lyme Regis with the 311 00:17:24,900 --> 00:17:27,900 lower Jurassic on the other side of Southwest England and summer 312 00:17:27,900 --> 00:17:32,300 said, you can see that the Lyme Regis section is extremely 313 00:17:32,300 --> 00:17:34,800 condensed with respect to the somerset section. 314 00:17:35,700 --> 00:17:38,900 And you can actually identify particular bedding planes where 315 00:17:38,900 --> 00:17:41,600 stuff has to be missing based on missing every night. 316 00:17:41,600 --> 00:17:44,100 Sounds and I've been and looked at them and the crawled all over 317 00:17:44,100 --> 00:17:46,000 them. Oliver, there is nothing. 318 00:17:46,700 --> 00:17:50,100 You find a few scattered economic aid, spines and a sharp 319 00:17:50,100 --> 00:17:53,600 bedding plane on a calcareous limestone and that's it. 320 00:17:53,900 --> 00:17:58,500 And yet, the evidence is saying that several tens 200,000 years 321 00:17:59,100 --> 00:18:00,900 is missing on that particular surface. 322 00:18:00,900 --> 00:18:03,800 It's really frightening. It's really frightening because 323 00:18:03,800 --> 00:18:06,300 if you didn't have the more complete Section, you wouldn't 324 00:18:06,300 --> 00:18:08,500 know that's coming back to your earlier question. 325 00:18:08,800 --> 00:18:12,900 You also mention our desire to use the sedimentary record to 326 00:18:12,900 --> 00:18:16,900 understand the environments in which fossils lived in perished, 327 00:18:17,500 --> 00:18:21,500 what sort of bias affects the record then, how can we overcome 328 00:18:21,500 --> 00:18:24,400 their effects? Actually, the paleontologists of 329 00:18:24,400 --> 00:18:27,100 studied preservation potential a much more detailed and 330 00:18:27,100 --> 00:18:28,900 sedimentology is from for a longer period of time. 331 00:18:28,900 --> 00:18:31,500 There's a whole branch of paleontology called to follow me 332 00:18:32,200 --> 00:18:34,700 which is the study of what happens to things when they die. 333 00:18:35,500 --> 00:18:37,800 The extent to, which soft tissues, get preserved, and 334 00:18:37,800 --> 00:18:41,200 also, how you can reconstruct how things came to Die. 335 00:18:41,600 --> 00:18:44,800 The biases in the record. I think the most obvious one in 336 00:18:44,800 --> 00:18:48,200 paleontology is dissolution. So, the sedimentary record is 337 00:18:48,200 --> 00:18:50,000 incomplete. Not only through erosion but 338 00:18:50,000 --> 00:18:52,400 also just dissolution of material. 339 00:18:52,400 --> 00:18:56,400 It's very common in sedimentary sequences to only find 340 00:18:56,600 --> 00:18:59,300 particular fossils. An example would be finding 341 00:18:59,300 --> 00:19:02,800 oysters and economic needs and nothing else. 342 00:19:03,300 --> 00:19:05,300 There's a formation we're working on in a moment. 343 00:19:05,400 --> 00:19:07,600 And at the moment and that's the situation there. 344 00:19:08,000 --> 00:19:13,100 And the reason is that those are calcitic forms and many of the 345 00:19:13,800 --> 00:19:15,500 animals that would have lived at the same time. 346 00:19:15,500 --> 00:19:18,200 Precipitated shells from aragonite and those are 347 00:19:18,200 --> 00:19:20,200 agonistic forms of subsequently been dissolved. 348 00:19:20,200 --> 00:19:23,200 So you've got a preservation bias towards the calcitic forms, 349 00:19:23,300 --> 00:19:26,800 more robust forms, obviously hard bodies as opposed to soft 350 00:19:26,800 --> 00:19:30,800 bodied organisms and then as far as the sediments themselves are 351 00:19:30,808 --> 00:19:34,100 concerned, you preserve the organisms which live in the 352 00:19:34,100 --> 00:19:35,800 sediments, which get preserved. It. 353 00:19:36,700 --> 00:19:39,700 So the organisms, which were happy living in the bottom of a 354 00:19:39,700 --> 00:19:42,900 fast-flowing title Channel, stand a chance of being 355 00:19:42,900 --> 00:19:45,700 preserved, the razor shells, which were at the same time, 356 00:19:45,700 --> 00:19:50,500 living in the tidal Flats which are not being preserved, don't 357 00:19:50,500 --> 00:19:53,400 get preserved. So, it comes with the territory, 358 00:19:53,400 --> 00:19:56,300 the sort of bulk preservation of the sedimentary record as well. 359 00:19:56,900 --> 00:20:01,500 Okay, let's talk about reconstructing discrete events, 360 00:20:01,500 --> 00:20:03,100 that occurred in the geological past. 361 00:20:03,400 --> 00:20:05,300 First of all, what kind of events are you referring? 362 00:20:05,400 --> 00:20:07,400 Dying to hear. So, I'm thinking of the 363 00:20:07,400 --> 00:20:10,400 question, you have an intubated sequence of sounds and modes. 364 00:20:10,400 --> 00:20:12,900 For example, maybe it's a shallow Marine sequence and 365 00:20:12,900 --> 00:20:15,900 you'd like to say something about the intensity of storms. 366 00:20:16,700 --> 00:20:20,600 So I think these are individual graded beds, so they fine 367 00:20:20,600 --> 00:20:22,200 upwards. They're deposited by discrete 368 00:20:22,200 --> 00:20:25,100 events of flows, which are waning over time and hence 369 00:20:25,100 --> 00:20:28,000 depositing. So how strong were they can I 370 00:20:28,000 --> 00:20:31,200 say anything about the relative strength of storm intensity here 371 00:20:31,200 --> 00:20:33,800 versus there? The type of Coast the same for 372 00:20:33,800 --> 00:20:37,400 floods are these Rivers Characterized by very strong 373 00:20:37,400 --> 00:20:41,400 flows seasonally or you could average flows over a long 374 00:20:41,400 --> 00:20:43,500 periods of time in a sort of temperate setting. 375 00:20:43,500 --> 00:20:45,900 What can we say about those kind of situations? 376 00:20:46,600 --> 00:20:48,800 It's a very interesting problem because there was a classical 377 00:20:48,800 --> 00:20:52,100 study done on the coast of Southern California, where they 378 00:20:52,100 --> 00:20:55,800 asked that question of modern shallow Marine sediments whose 379 00:20:55,800 --> 00:20:59,000 age they knew, because they repeatedly surveyed the shelf 380 00:20:59,000 --> 00:21:02,500 and they knew when the deposits have arrived and what they were 381 00:21:02,500 --> 00:21:06,900 able to show was that it was Highly contingent what got 382 00:21:06,900 --> 00:21:09,900 deposited. So firstly, in order for 383 00:21:09,900 --> 00:21:13,100 something to be recognizable in the shallow Marine record, it 384 00:21:13,100 --> 00:21:14,900 should not be burrowed to destruction. 385 00:21:14,900 --> 00:21:19,400 So if you just deposit after a storm, a graded sand bed, and it 386 00:21:19,400 --> 00:21:22,900 stays within about 10, cm to the surface and the burrowing 387 00:21:23,200 --> 00:21:25,600 Foreigner at the bottom of the sea, just destroy it, and it 388 00:21:25,600 --> 00:21:28,000 becomes unrecognizable. All the sand grains are moved 389 00:21:28,000 --> 00:21:30,500 around, you can't recognize it as a bed anymore. 390 00:21:31,100 --> 00:21:35,800 So in order to be preserved, it has to be insulated from Going, 391 00:21:35,900 --> 00:21:39,200 which means buried below the Zone in which the animals live. 392 00:21:39,700 --> 00:21:42,100 So the most important thing for preservation is that something 393 00:21:42,100 --> 00:21:45,000 happens afterwards. It's nothing about the event 394 00:21:45,000 --> 00:21:48,400 itself, but it what happens, subsequently you need a rapid 395 00:21:48,400 --> 00:21:52,000 other event which buries it. So it's telling you nothing 396 00:21:52,000 --> 00:21:57,000 about the magnitude and then they tracked these storm layers 397 00:21:57,000 --> 00:21:59,700 back into the flood basins of the rivers from which they've 398 00:21:59,700 --> 00:22:03,300 been derived and they were able to show that the amount of 399 00:22:03,300 --> 00:22:05,800 material that was being transported to the a shelf in 400 00:22:05,800 --> 00:22:08,900 the first place, had nothing to do with the intensity of the 401 00:22:08,900 --> 00:22:15,500 storm or the flow in the river. It was the event which occurred 402 00:22:15,500 --> 00:22:18,700 the rainfall event, which occurred when the river was 403 00:22:18,700 --> 00:22:22,800 already full of sediment. So previous events had push 404 00:22:22,800 --> 00:22:25,600 sediment from the hill, slopes into the river and the sediments 405 00:22:25,600 --> 00:22:29,100 were in the bars and banks of the river and the bottom of the 406 00:22:29,100 --> 00:22:31,800 river. And it was only when the river 407 00:22:31,800 --> 00:22:34,400 was actually full of sediment that a next event flushed, it 408 00:22:34,400 --> 00:22:37,400 all out to sea. So it was highly contingent. 409 00:22:37,400 --> 00:22:40,200 What got preserve, it was a flood event which happened to 410 00:22:40,200 --> 00:22:44,200 occur when the river was full deposited on the shelf and then 411 00:22:44,300 --> 00:22:46,900 the Shelf event, which happened to be preserved because 412 00:22:46,900 --> 00:22:50,600 something else happened later. So the conclusion is that the 413 00:22:50,600 --> 00:22:54,400 record is highly contingent. And actually almost impossible 414 00:22:54,700 --> 00:22:57,800 on a bed by bed bases, to reconstruct. 415 00:22:57,800 --> 00:23:01,200 So, that's kind of disappointing in terms of what we could 416 00:23:01,200 --> 00:23:04,000 extract from the record but I find it fascinating in the sense 417 00:23:04,000 --> 00:23:08,700 that as scientists. We are taught to see a record, a 418 00:23:08,700 --> 00:23:12,100 sequence of events and interpret it deterministically. 419 00:23:12,300 --> 00:23:14,700 And we don't give perhaps enough credit to the chaotic 420 00:23:14,700 --> 00:23:18,400 interpretation, where a bunch of nonlinear functions are actually 421 00:23:18,400 --> 00:23:21,400 combining to produce a signal which we wish to interpret 422 00:23:21,400 --> 00:23:23,900 deterministic because that's how we've been educated. 423 00:23:24,000 --> 00:23:26,600 But in fact, there is no meaningful deterministic 424 00:23:26,600 --> 00:23:28,700 explanation that we can extract from it. 425 00:23:29,400 --> 00:23:32,600 If only, we were back there, we could have a time-travel machine 426 00:23:32,600 --> 00:23:34,300 and then we'd know actually what happened. 427 00:23:34,300 --> 00:23:37,600 But in fact you're saying that, Contingency both on what 428 00:23:37,600 --> 00:23:42,600 happened prior and what happened after interferes with what 429 00:23:42,600 --> 00:23:47,900 happens in any given time, so it can just be two scrambled up, 430 00:23:47,900 --> 00:23:50,000 too much information. Lost to be able to accurately 431 00:23:50,000 --> 00:23:52,400 reconstruct. Yes, people are working on this 432 00:23:52,400 --> 00:23:54,700 on different scales. I described it on a small scale 433 00:23:54,700 --> 00:23:57,300 there but on a landscape Evolution scale or a larger 434 00:23:57,300 --> 00:23:59,700 scale. What we want to do is extract 435 00:23:59,700 --> 00:24:02,300 the external forcings of a particular event. 436 00:24:02,300 --> 00:24:04,500 So how big was the hurricane? How big was the storm? 437 00:24:04,500 --> 00:24:08,000 How big was the flood or how long was the Ice Age? 438 00:24:08,000 --> 00:24:11,300 How big was the ice age or you can scale this up to what extent 439 00:24:11,300 --> 00:24:14,500 did sediment input change or did the sea level for all? 440 00:24:14,900 --> 00:24:18,200 These are alternative ways of making a coastline move forward 441 00:24:18,200 --> 00:24:21,900 into the ocean, for example, and people talk of signal shredding. 442 00:24:22,000 --> 00:24:25,500 It's a term, I quite like is that the interplay of all the 443 00:24:25,500 --> 00:24:28,400 processes which are involved in bringing that sediment to the 444 00:24:28,400 --> 00:24:31,200 coast, the storage, in the floodplain, they're sweeping out 445 00:24:31,200 --> 00:24:34,600 by subsequent floods, they're actually shredding the input 446 00:24:34,600 --> 00:24:36,300 signal. You're absolutely right. 447 00:24:36,300 --> 00:24:38,100 If you were there. If someone could have observed, 448 00:24:38,100 --> 00:24:41,300 everything that happened but reconstructing it from the 449 00:24:41,300 --> 00:24:46,500 result and inferring a proximate, cause the warning 450 00:24:46,500 --> 00:24:49,200 signs are there from the modern studies, that, that is an 451 00:24:49,200 --> 00:24:52,700 extremely difficult exercise. And again, I'm concerned about 452 00:24:52,700 --> 00:24:55,600 what we said earlier which is, is there evidence for the record 453 00:24:55,600 --> 00:24:58,900 that the shredding has taken place, or might we just simply 454 00:24:58,900 --> 00:25:02,700 blindly assumed that what we're seeing is the faithful record. 455 00:25:02,800 --> 00:25:05,200 Well, this comes to the point of what is the null. 456 00:25:05,300 --> 00:25:08,000 Offices with which you approach the geological record and I 457 00:25:08,000 --> 00:25:10,000 think that's my Essential philosophical point. 458 00:25:10,000 --> 00:25:14,000 You know, I believe that before allocating and external, cause 459 00:25:14,700 --> 00:25:18,700 you need to rule out the chaotic interpretation, you need to rule 460 00:25:18,700 --> 00:25:21,900 out the autogenic interpretation by autogenic. 461 00:25:21,900 --> 00:25:25,300 I mean the processes which are intrinsic to a sedimentary 462 00:25:25,300 --> 00:25:29,000 environment. So the and has migrated sideways 463 00:25:29,000 --> 00:25:33,600 and spits, pro-grade into tidal inlets and barriers, smooth land 464 00:25:33,600 --> 00:25:37,200 words and all of these things. Are happening just by virtue of 465 00:25:37,208 --> 00:25:40,200 natural variability. There's nothing happening to sea 466 00:25:40,200 --> 00:25:43,000 level necessarily or sediment Supply or tectonics, which is 467 00:25:43,000 --> 00:25:48,600 controlling those and only, when you've ruled those out, are you 468 00:25:48,600 --> 00:25:53,000 kind of allowed to go forward and invoke an external? 469 00:25:53,300 --> 00:25:55,800 Cause that's the way I was brought up as a sedimentology. 470 00:25:55,800 --> 00:25:59,200 She used to say that the sedimentology sprayer was Lord, 471 00:25:59,200 --> 00:26:02,700 forgive us our transgressions because we would never invoke a 472 00:26:02,700 --> 00:26:04,600 transgression. And this we had to because there 473 00:26:04,600 --> 00:26:06,700 was no way out. Out of the particular situation 474 00:26:06,700 --> 00:26:09,000 and it strikes me that there's been a bit of a swing of the 475 00:26:09,000 --> 00:26:13,100 pendulum, the other way that people are very eager to move 476 00:26:13,100 --> 00:26:16,700 straight to external forcing. And there are a number of deep 477 00:26:16,700 --> 00:26:20,800 statistical debates as to what the null hypothesis should be 478 00:26:20,900 --> 00:26:24,600 when you claim to see a signal in the sedimentary record, 479 00:26:24,600 --> 00:26:27,200 particularly with this astronomical timescale tuning 480 00:26:27,700 --> 00:26:32,900 and it is not a simple question. You also mention that we'd like 481 00:26:32,900 --> 00:26:36,000 to be able to reconstruct the environment in which the 482 00:26:36,000 --> 00:26:39,100 deposition we see preserved today took place. 483 00:26:40,000 --> 00:26:43,800 Are you talking about things, like whether it was wind-borne 484 00:26:43,800 --> 00:26:48,600 or waterborne, or if it was a water deposit, whether it was 485 00:26:48,600 --> 00:26:52,800 Marine Fluval or from a lake, yes, that's why you'd start off. 486 00:26:53,300 --> 00:26:56,300 And then what we would typically need to do is to go down to the 487 00:26:56,300 --> 00:26:58,900 next level of detail. So if it's within the lake, is 488 00:26:58,900 --> 00:27:00,400 it the beach of a lake lies at the bottom? 489 00:27:00,600 --> 00:27:02,500 Of the lake. Or is it a Delta coming into the 490 00:27:02,500 --> 00:27:05,000 lake? So what we're trying to do is 491 00:27:05,000 --> 00:27:06,900 reconstruct the three-dimensional shape of the 492 00:27:06,900 --> 00:27:10,400 sedimentary bodies that have been preserved, such that we can 493 00:27:10,500 --> 00:27:13,900 either store fluids in the, my carbon dioxide or extract fluids 494 00:27:13,900 --> 00:27:17,900 like water, or oil and gas, or build things on top of them. 495 00:27:17,900 --> 00:27:20,400 So, we'll find a solid footing for our piles. 496 00:27:20,400 --> 00:27:22,300 For instance, for Coastal defenses. 497 00:27:22,300 --> 00:27:25,200 As sea levels rise. So, we need to know where 498 00:27:25,500 --> 00:27:28,300 physically these different, litha somes, these different 499 00:27:28,300 --> 00:27:30,300 little logical bodies actually are. 500 00:27:30,300 --> 00:27:33,100 And What shape they are. So the trick there is to 501 00:27:33,100 --> 00:27:34,500 reconstruct the new position of model. 502 00:27:34,500 --> 00:27:37,800 So a river coming into a lake. For example, typically has low 503 00:27:37,800 --> 00:27:40,500 wave energy. So you see the channels 504 00:27:40,500 --> 00:27:42,700 protruding quite a lot into the lake? 505 00:27:42,700 --> 00:27:45,900 We sometimes call it a bird's foot Delta, because it looks 506 00:27:45,900 --> 00:27:49,000 like the three toes of a bird's foot, as it migrates into the 507 00:27:49,000 --> 00:27:51,900 lake and bigger Lakes, you would see wavery working and you would 508 00:27:51,900 --> 00:27:55,200 end up with smooth, cusp, 8, shorelines for instance, from 509 00:27:55,200 --> 00:27:59,300 the waves. And so those two types of Delta 510 00:27:59,300 --> 00:28:02,200 will give a different shape, Send bodies and we would like to 511 00:28:02,200 --> 00:28:05,000 reconstruct that. And the preservation Point here 512 00:28:05,000 --> 00:28:10,500 is that the body that we want to reconstruct is not simply the 513 00:28:10,500 --> 00:28:14,200 plan view of the body when it was deposited but what ends up 514 00:28:14,200 --> 00:28:18,300 being preserved over time and that depends on this overlay of 515 00:28:18,300 --> 00:28:21,300 erosion due to base level changing, for instance, in a 516 00:28:21,308 --> 00:28:24,400 lake based levels drop as the lake dries up and then they rise 517 00:28:24,400 --> 00:28:27,800 again, maybe on a seasonal basis and each of those base level 518 00:28:27,800 --> 00:28:31,400 lowerings will result in Channel indecision and Erosion of 519 00:28:31,400 --> 00:28:36,000 previous material and make level rising will result in the Strand 520 00:28:36,000 --> 00:28:40,000 plane and the beach truncating, the previous Delta material and 521 00:28:40,000 --> 00:28:42,100 wiping it out. So you have to reconstruct a 522 00:28:42,108 --> 00:28:45,300 three dimensional shape, which reflects the Deep additional 523 00:28:45,300 --> 00:28:47,100 model and the preservation of filter. 524 00:28:48,100 --> 00:28:51,700 It seems that there are actually a huge number of interacting 525 00:28:51,700 --> 00:28:56,100 processes and chance events that can affect what gets preserved. 526 00:28:56,700 --> 00:28:59,900 I wonder where you see the field going and whether perhaps you 527 00:28:59,900 --> 00:29:03,400 think that the Problem of discerning and accounting for 528 00:29:03,400 --> 00:29:07,000 preservation of bias is amenable to artificial intelligence and 529 00:29:07,008 --> 00:29:10,300 machine learning. It probably depends in part on 530 00:29:10,300 --> 00:29:13,800 whether we have a large enough data set of records for which we 531 00:29:13,800 --> 00:29:16,900 know the biases that can serve as training data for a model. 532 00:29:17,300 --> 00:29:20,100 That's a really good point. It strikes me that this problem 533 00:29:20,100 --> 00:29:25,300 that we've got of disentangling, multiple interrelated processes 534 00:29:25,500 --> 00:29:30,900 which have feedbacks between them is one which, Out AI, 535 00:29:30,900 --> 00:29:33,800 you're not going to solve this, put it that way and I think 536 00:29:33,800 --> 00:29:35,900 there is hope there and I'm looking forward to a literature 537 00:29:35,900 --> 00:29:39,900 emerging on that topic. In an earlier podcast, Paul 538 00:29:39,900 --> 00:29:43,600 Hoffman laid out convincing evidence for the snowball Earth 539 00:29:43,600 --> 00:29:47,500 hypothesis, which posits that there are two periods during the 540 00:29:47,500 --> 00:29:50,700 late proterozoic, during which the Earth was completely frozen 541 00:29:50,700 --> 00:29:52,500 over. As I mentioned in my 542 00:29:52,500 --> 00:29:55,900 introduction, you studied a sequence of glacial, deposits 543 00:29:55,900 --> 00:29:58,800 and South West Scotland, corresponding to the earlier of 544 00:29:58,800 --> 00:30:01,500 these two periods. So as to develop, A deeper 545 00:30:01,500 --> 00:30:03,900 understanding of the preservation of bias that might 546 00:30:03,900 --> 00:30:07,100 have been operating there. Can you tell us about that? 547 00:30:07,300 --> 00:30:10,400 Yeah, this unit is the port Escape formation in Southwest 548 00:30:10,400 --> 00:30:14,600 Scotland and it's dirty and it's the older of the two cryogenian 549 00:30:14,600 --> 00:30:19,700 glaciations and it's exceptionally thick for a 30 and 550 00:30:19,700 --> 00:30:22,800 sequins. And the reason why is 551 00:30:22,800 --> 00:30:25,500 exceptionally thick is that the deposits have been preserved in 552 00:30:25,500 --> 00:30:29,900 a basin, which were starting to rift at that time and so was 553 00:30:29,900 --> 00:30:31,400 very Lovely. Subsiding. 554 00:30:32,100 --> 00:30:37,200 And what that enables us to see is that we have a series of 555 00:30:37,200 --> 00:30:40,500 alternations between glacial and non glacial depositional 556 00:30:40,500 --> 00:30:43,100 environments. So we can clearly demonstrate 557 00:30:43,100 --> 00:30:45,400 that ice was advancing and retreating. 558 00:30:45,400 --> 00:30:47,400 We could demonstrate that the ice was grounded. 559 00:30:47,400 --> 00:30:50,300 We have lots of Glacier, click taluk features which indicate 560 00:30:50,300 --> 00:30:53,200 the advance of ice over land surface and we have lots of 561 00:30:53,200 --> 00:30:57,100 periglacial features which indicate the exposure of a land 562 00:30:57,100 --> 00:31:00,800 surface to the air. And we have glacial flow of your 563 00:31:00,800 --> 00:31:03,100 glacial Coastline and Glacial Marine deposits. 564 00:31:03,500 --> 00:31:06,800 So we can demonstrate that there was an active hydrological cycle 565 00:31:06,800 --> 00:31:09,700 during that time and the planet wasn't completely Frozen during 566 00:31:09,700 --> 00:31:13,900 the deposition of that material. Now in the classical snowball, 567 00:31:14,100 --> 00:31:17,400 which I think is not fully believed in its hardest 568 00:31:17,400 --> 00:31:21,200 theoretical form anymore. It posited that the entire Earth 569 00:31:21,200 --> 00:31:25,600 was frozen at that time and a bit of an issue there. 570 00:31:25,600 --> 00:31:29,700 With this particular sequence is that if the Earth Was totally 571 00:31:29,700 --> 00:31:31,800 frozen. And there was nothing happening 572 00:31:32,000 --> 00:31:35,300 based on substance, wouldn't really know about that and 573 00:31:35,300 --> 00:31:37,400 basins would continue to subside. 574 00:31:37,800 --> 00:31:41,100 There's no reason why rifting process has stopped because the 575 00:31:41,100 --> 00:31:43,200 Earth got a little bit cold on the surface. 576 00:31:44,100 --> 00:31:47,600 And therefore, if there was no sediment input into a basement, 577 00:31:47,600 --> 00:31:50,300 because the entire Earth was frozen, you would create large 578 00:31:50,300 --> 00:31:53,000 holes in the ground. And when sedimentation 579 00:31:53,000 --> 00:31:56,700 restarted, you'd have to start in relatively deep water, 580 00:31:57,300 --> 00:32:00,500 filling up, those holes. So, the ice would melt, the 581 00:32:00,500 --> 00:32:02,400 holes will be filled. And then the sentiment would 582 00:32:02,400 --> 00:32:05,800 arrive perhaps as the ice melted into these holes, and that is 583 00:32:05,800 --> 00:32:08,500 not the sequence that we see in Southwest Scotland. 584 00:32:08,500 --> 00:32:12,500 So, we feel that we're adding detail to the nature of the 585 00:32:12,500 --> 00:32:14,900 snowball Earth. What you working on at the 586 00:32:14,900 --> 00:32:17,700 moment? I'm editing the successor to a 587 00:32:17,700 --> 00:32:21,000 standard, sedimentology text book that was published in 1996 588 00:32:21,000 --> 00:32:22,800 by Harold, reading and co-workers. 589 00:32:22,800 --> 00:32:25,200 And her breathing was my supervisor, it's called 590 00:32:25,200 --> 00:32:28,700 sedimentary environments, processes and fasces, one of the 591 00:32:28,800 --> 00:32:31,500 Why I wanted to take that up? Was this point that I wanted to 592 00:32:31,500 --> 00:32:35,700 bring an understanding of preservation to the D positional 593 00:32:35,700 --> 00:32:38,200 models in the next update of that book? 594 00:32:38,300 --> 00:32:40,700 And then another project together with a guy we both 595 00:32:40,700 --> 00:32:44,000 know, I think droste and Mike. So we're working on the 596 00:32:44,000 --> 00:32:46,400 sediments, that were deposited during the Abduction of the 597 00:32:46,400 --> 00:32:49,700 ophiolite in our man. So trying to understand from the 598 00:32:49,700 --> 00:32:53,100 sedimentary record, what we can deduce about, how the continent 599 00:32:53,100 --> 00:32:57,900 reacted to the Loading by the ophiolite slab when it ended up 600 00:32:57,900 --> 00:33:00,800 on top of Mia. And that's turning out to be 601 00:33:00,800 --> 00:33:03,700 quite an interesting problem because what the healthy like 602 00:33:03,700 --> 00:33:07,600 slab did is it caused a carbonate platform to drown and 603 00:33:07,600 --> 00:33:10,600 when the carbonate platform drowned, there was no sediment 604 00:33:10,600 --> 00:33:13,000 production because it became too deep. 605 00:33:13,200 --> 00:33:17,700 So in essence, we have a record of water depth being created 606 00:33:18,100 --> 00:33:22,000 without a sediment in filter record what actually happened in 607 00:33:22,000 --> 00:33:23,700 detail during the abduction process. 608 00:33:23,700 --> 00:33:27,600 So it's a staffed sedimentary Basin sort of an extreme example 609 00:33:28,100 --> 00:33:31,200 where you Reconstruct the record because sediment Supply was so 610 00:33:31,200 --> 00:33:33,600 little that it's not been documented. 611 00:33:34,600 --> 00:33:36,500 Bruce level, thank you very much. 612 00:33:36,600 --> 00:33:39,800 You're welcome. It was fun for more about 613 00:33:39,800 --> 00:33:44,000 geology b as well as pictures and illustrations that support 614 00:33:44,000 --> 00:33:46,800 this podcast, go to geology B.com.