1 00:00:04,900 --> 00:00:10,900 This is Jala g b with Oliver stimple. the history of complex 2 00:00:10,900 --> 00:00:14,300 life on Earth has been punctuated by mass extinctions, 3 00:00:15,000 --> 00:00:19,500 five of these extinctions, the so-called Big Five stand out as 4 00:00:19,500 --> 00:00:23,300 being particularly lethal one, at the end of the ordovician, 5 00:00:23,900 --> 00:00:27,800 one in the late devonian, and those at the end of the Permian, 6 00:00:27,800 --> 00:00:33,500 Triassic and Cretaceous, But the sedimentary record also tells us 7 00:00:33,500 --> 00:00:37,400 that there have been a total of 31 significant disruptions to 8 00:00:37,400 --> 00:00:40,800 the Earth environment since the beginning of the phanerozoic, 9 00:00:41,100 --> 00:00:45,900 542 million years ago. So why did only five of them 10 00:00:45,900 --> 00:00:47,900 lead to catastrophic mass extinction? 11 00:00:48,500 --> 00:00:51,300 And can we compare the disruptions to the environment 12 00:00:51,300 --> 00:00:54,600 that we see in the geological record with the one being cause 13 00:00:54,600 --> 00:00:59,000 now by human activities? Dan Rothman has tackled these 14 00:00:59,000 --> 00:01:01,700 questions by studying, disruptions to the Earth's 15 00:01:01,700 --> 00:01:05,800 carbon cycle as revealed by high-resolution, measurements of 16 00:01:05,800 --> 00:01:08,800 carbon isotope ratios within carbonate, rocks. 17 00:01:09,800 --> 00:01:13,700 His results indicate that the Earth system has a critical rate 18 00:01:13,700 --> 00:01:18,200 of change. Over long timescales disruptions 19 00:01:18,200 --> 00:01:21,900 occur when the rate of change in the amount of carbon injected 20 00:01:21,900 --> 00:01:25,000 into the Earth system exceeds this rate. 21 00:01:26,100 --> 00:01:29,300 And they also hypothesize has that it short time, scales 22 00:01:29,700 --> 00:01:32,600 disruptions occur. If the amount of the carbon 23 00:01:32,600 --> 00:01:36,900 injected exceeds a critical size, Dan. 24 00:01:36,900 --> 00:01:39,800 Rothman, is Professor of geophysics at the Massachusetts 25 00:01:39,800 --> 00:01:42,900 Institute of Technology. Dan Rothman. 26 00:01:42,900 --> 00:01:46,300 Welcome to geology B. Thank you delighted to be here. 27 00:01:46,800 --> 00:01:50,500 As I said in my introduction. You focused on the carbon cycle 28 00:01:50,500 --> 00:01:53,400 as an indicator of disruption to the Earth system. 29 00:01:54,300 --> 00:01:57,500 What exactly do you mean by the Earth's system here? 30 00:01:57,500 --> 00:02:00,500 And can you remind us as to how the carbon cycle works? 31 00:02:00,900 --> 00:02:05,200 I think of the earth system as a combination of the physical and 32 00:02:05,200 --> 00:02:08,300 chemical. Ant with life, which you might 33 00:02:08,300 --> 00:02:10,500 think of as the biological environment. 34 00:02:10,900 --> 00:02:14,700 So, the Earth System Dynamics, which is what this work. 35 00:02:14,700 --> 00:02:19,600 Addresses has to do with the interaction of life and physical 36 00:02:19,600 --> 00:02:23,300 / chemical environment. Your second question was about 37 00:02:23,300 --> 00:02:27,600 the carbon cycle the carbon cycle to a significant extent is 38 00:02:27,600 --> 00:02:29,500 where our System Dynamics happen. 39 00:02:29,500 --> 00:02:32,500 The carbon cycle is kind of the locus of the interaction of life 40 00:02:32,500 --> 00:02:36,300 in the environment. What it is precisely plants. 41 00:02:36,500 --> 00:02:38,400 Take up CO2 out of the atmosphere. 42 00:02:38,400 --> 00:02:44,100 Also out of the oceans and consuming organisms like us eat, 43 00:02:44,100 --> 00:02:48,600 either the products of photosynthesis or the animals 44 00:02:48,600 --> 00:02:51,900 that lived off of photosynthesis and in doing. 45 00:02:51,900 --> 00:02:55,300 So, we return the original organic plant matter. 46 00:02:55,300 --> 00:02:58,800 The matter that was fixed back to the atmosphere and oceans. 47 00:02:59,000 --> 00:03:04,300 So CO2 goes to organic carbon via photosynthesis and consuming 48 00:03:04,300 --> 00:03:08,100 organisms return it back. The process of consumption is 49 00:03:08,100 --> 00:03:10,000 typically referred to as respiration. 50 00:03:10,000 --> 00:03:15,800 So if we look at the carbon cycle, does that enable us to 51 00:03:15,800 --> 00:03:19,300 infer what the physical environment was at the time, 52 00:03:19,300 --> 00:03:22,500 things like the temperature and the composition of the 53 00:03:22,500 --> 00:03:27,700 atmosphere. It allows us to identify when 54 00:03:27,700 --> 00:03:30,900 disruptions to the environment occurred. 55 00:03:30,900 --> 00:03:34,700 So one can think of the carbon cycle as a loop between 56 00:03:34,700 --> 00:03:36,800 photosynthesis and respiration. Asian. 57 00:03:36,800 --> 00:03:39,900 Typically, there are given the impression that the carbon cycle 58 00:03:39,900 --> 00:03:44,300 is in balance, that is nature is thought to be in Balance. 59 00:03:44,800 --> 00:03:48,800 However, as is well known at present because of fossil fuel 60 00:03:48,800 --> 00:03:52,800 burning, we're stressing it out of balance, but there's a very 61 00:03:52,800 --> 00:03:55,800 important question that asks, whether the carbon cycle has in 62 00:03:55,800 --> 00:03:58,300 some sense, been unbalanced in the past. 63 00:03:59,200 --> 00:04:05,100 And if one looks at the geologic record, the answer is pretty 64 00:04:05,100 --> 00:04:07,500 much unequivocally. Yes, it has. 65 00:04:08,100 --> 00:04:11,400 And then the question is, why, and how do we know this? 66 00:04:11,400 --> 00:04:14,800 We know this because of chemical traces, that are stored in 67 00:04:14,800 --> 00:04:18,100 sedimentary rocks in the form of the isotopic, composition a 68 00:04:18,100 --> 00:04:22,200 carbonate minerals and also organic matter and these 69 00:04:22,300 --> 00:04:26,300 isotopic compositions change and sometimes they change abruptly. 70 00:04:27,200 --> 00:04:30,500 And most curiously, they change abruptly. 71 00:04:30,500 --> 00:04:33,900 Every time there is a mass extinction, all the rocks that 72 00:04:33,900 --> 00:04:38,600 contain these records formed from It's of inorganic origin or 73 00:04:38,600 --> 00:04:41,800 of organic origin. And where does one find them 74 00:04:42,600 --> 00:04:47,200 formed from carbonate? Which in some cases is, simply 75 00:04:47,200 --> 00:04:50,300 the precipitation of carbonate minerals at the seafloor. 76 00:04:50,600 --> 00:04:54,700 And in other cases, is the remains of calcifying organisms. 77 00:04:54,800 --> 00:04:57,300 And that's a more recent case when I say more recent here. 78 00:04:57,300 --> 00:05:00,100 I mean, since the tree Asik, when calcifying 79 00:05:00,100 --> 00:05:04,100 photosynthesizers existed, the data I used study bulk 80 00:05:04,100 --> 00:05:05,900 carbonate. They're not focused on any 81 00:05:05,900 --> 00:05:07,400 particular. Ocular species. 82 00:05:07,400 --> 00:05:11,400 I did that to maintain a uniformity in the record and 83 00:05:11,400 --> 00:05:15,400 I've looked at data that come from a wide range of sources, 84 00:05:15,400 --> 00:05:19,400 outcrops for the oldest data and deep-sea drill cores for the 85 00:05:19,400 --> 00:05:24,100 much more recent data. The focus is not so much on the 86 00:05:24,100 --> 00:05:26,500 long-term evolution of the carbon cycle. 87 00:05:26,500 --> 00:05:29,600 But rather on its disruptions in a sense. 88 00:05:29,600 --> 00:05:33,600 What I've done is a little bit, akin to a seismologist who 89 00:05:33,600 --> 00:05:36,300 studies earthquakes only but not the long. 90 00:05:36,400 --> 00:05:39,700 Tectonic changes associated with just the burp. 91 00:05:39,700 --> 00:05:42,800 You know, the blast the disruption as I call it, and the 92 00:05:42,808 --> 00:05:46,300 cycle itself and there's a distribution of sizes of 93 00:05:46,300 --> 00:05:50,000 disruptions on the rates at which disruptions occur. 94 00:05:50,200 --> 00:05:53,700 So I made a catalog of those. Okay, so you mentioned Isotopes. 95 00:05:53,700 --> 00:05:57,800 So what exactly is measured in these carbonate, rocks that 96 00:05:57,900 --> 00:06:00,800 enables you to track the disruptions in the carbon cycle? 97 00:06:01,200 --> 00:06:07,500 What geocanvas do is to measure the ratio of The heavy stable, 98 00:06:07,500 --> 00:06:12,500 isotope of carbon, the abundance of it, carbon-13 to the lighter 99 00:06:12,500 --> 00:06:14,700 stable isotope, which is carbon 12. 100 00:06:14,700 --> 00:06:20,000 Carbon 12 is 99% of the world's carbon carbon. 13, is nearly the 101 00:06:20,000 --> 00:06:23,900 remaining 1% carbon 14, which everybody likes to think of as 102 00:06:23,900 --> 00:06:27,400 the isotope of carbon is actually very minor and it 103 00:06:27,400 --> 00:06:29,800 decays with a half-life of several thousand years. 104 00:06:29,800 --> 00:06:33,600 So it's not in the picture and what we're looking at is ratios 105 00:06:33,600 --> 00:06:37,700 of stable isotopes, the point that so Measurements, is that 106 00:06:37,800 --> 00:06:41,900 these ratios change with time? And the reason they change is 107 00:06:41,900 --> 00:06:48,600 because photosynthesis being a fast kinetic, reaction favors 108 00:06:48,600 --> 00:06:53,400 the lighter, isotope of carbon. So the organic matter is 109 00:06:53,400 --> 00:06:57,700 isotopically lighter than the CO2 from which it comes and by 110 00:06:57,800 --> 00:07:01,400 about twenty eight parts per thousand. 111 00:07:02,000 --> 00:07:07,500 And when carbon is buried in sediments, If or when there is 112 00:07:07,500 --> 00:07:11,500 an imbalance in the carbon cycle, which is reflected in 113 00:07:11,500 --> 00:07:15,700 makes of burial, then these isotopic ratios change. 114 00:07:15,800 --> 00:07:19,500 And most of the time they're just changing modestly and 115 00:07:19,500 --> 00:07:24,200 slowly but sometimes they change more abruptly and significantly. 116 00:07:24,600 --> 00:07:28,200 So, as you said, a moment ago, you focus on those periods when 117 00:07:28,200 --> 00:07:31,700 the change was abrupt. So, I guess it's a spike in the 118 00:07:31,700 --> 00:07:35,400 ratio of carbon-13 to carbon-12. Is that right? 119 00:07:35,600 --> 00:07:39,400 It's Spike, when you across the room. 120 00:07:39,400 --> 00:07:43,800 So to speak, A Thousand Miles High, it may play out over tens 121 00:07:43,800 --> 00:07:47,300 of thousands or hundreds of thousands of years, but it's a 122 00:07:47,300 --> 00:07:50,900 spike in geologic time. Yes, so that's a nice way of 123 00:07:50,900 --> 00:07:54,700 putting it, but do the geological records that you're 124 00:07:54,700 --> 00:07:59,500 analyzing permit you to resolve detail within each Spike, or is 125 00:07:59,500 --> 00:08:06,200 it just like one event, the two parameters that I focused on 10? 126 00:08:06,300 --> 00:08:10,000 And to be the best resolve ability and those two parameters 127 00:08:10,000 --> 00:08:14,700 are essentially the size of the disruption and that's basically 128 00:08:14,700 --> 00:08:19,900 how much the ratio of C 13 to see 12 changes and the time 129 00:08:19,900 --> 00:08:23,300 scale over which it changes it is the time scale over which the 130 00:08:23,300 --> 00:08:25,700 carbon cycle is stressed out at equilibrium. 131 00:08:26,400 --> 00:08:29,100 How long does it take to ramp up to its apogee? 132 00:08:29,100 --> 00:08:32,000 So, to speak when the disruption is at its peak, okay? 133 00:08:32,000 --> 00:08:36,700 So the size of that Peak, that you were able to measure, That 134 00:08:36,700 --> 00:08:39,500 is the size of the change in the isotope ratio. 135 00:08:39,500 --> 00:08:43,400 And so, you're connecting that to the mass say of the amount of 136 00:08:43,400 --> 00:08:46,000 carbon that would have been injected into the system at that 137 00:08:46,000 --> 00:08:47,600 time. Exactly. 138 00:08:47,600 --> 00:08:52,900 So the underlying hypothesis, which is very, very reasonable. 139 00:08:53,000 --> 00:08:56,200 It motivates. This is that when there's such a 140 00:08:56,200 --> 00:08:59,600 change in the carbon cycle that represents an imbalance between 141 00:08:59,600 --> 00:09:04,300 photosynthesis and respiration. And so this imbalance has its 142 00:09:04,300 --> 00:09:08,500 own characteristic. Epic signature that known 143 00:09:08,800 --> 00:09:11,700 isotopic change due to the imbalance. 144 00:09:12,100 --> 00:09:17,500 We calculate how much mass was so to speak or reconfigured or 145 00:09:17,500 --> 00:09:20,600 be mobilized within the carbon cycle during the course of the 146 00:09:20,600 --> 00:09:22,900 event. That's a straightforward 147 00:09:22,900 --> 00:09:28,000 geochemical calculation, okay? So before we talk about how 148 00:09:28,000 --> 00:09:30,200 these events look, when you look at them over the whole of 149 00:09:30,200 --> 00:09:34,400 phanerozoic time, what kind of physical mechanism would 150 00:09:34,400 --> 00:09:38,000 underlie the injection? Enough carbon to create a spike 151 00:09:38,000 --> 00:09:41,700 in your isotope ratios. Well, any of a great many. 152 00:09:42,200 --> 00:09:46,500 So a popular one is excess anomalous. 153 00:09:46,500 --> 00:09:51,300 Especially intensive, volcanic activity, massive volcanism. 154 00:09:51,900 --> 00:09:55,400 Volcanic CO2 is isotopically light compared to our 155 00:09:55,400 --> 00:09:58,800 atmospheric CO2. And so if you see the carbon 156 00:09:58,800 --> 00:10:03,700 becoming significantly lighter, it's often a hypothesis that 157 00:10:03,700 --> 00:10:09,200 volcanism may be the culprit of Very, very popular hypothesis. 158 00:10:09,200 --> 00:10:14,000 Is the injection of methane into the atmosphere methane coming 159 00:10:14,000 --> 00:10:16,300 from methane clathrates in the ocean. 160 00:10:16,500 --> 00:10:20,800 Did you say methane clathrates? It's a solid form of methane, 161 00:10:20,800 --> 00:10:25,200 buried beneath the seafloor. When temperatures rise, they can 162 00:10:25,200 --> 00:10:28,600 be re mobilized within the carbon cycle, and this is 163 00:10:28,700 --> 00:10:31,700 methane. Typically of biogenic origin, 164 00:10:31,700 --> 00:10:35,400 but is Barry, but it has a way of coming back, that's an 165 00:10:35,408 --> 00:10:37,700 attractive hype. Austin says, because methane is 166 00:10:37,700 --> 00:10:41,300 very isotopically light compared to volcanic CO2 so you don't 167 00:10:41,300 --> 00:10:44,000 need as much of it to account for the data. 168 00:10:44,600 --> 00:10:48,000 Another very popular way of interpreting these things is by 169 00:10:48,000 --> 00:10:53,100 changing the relative fluxes in the burial of organic carbon, 170 00:10:53,100 --> 00:10:56,200 which is isotopically light. And the burial of carbonate 171 00:10:56,200 --> 00:10:58,700 carbon which is isotopically heavy. 172 00:10:58,700 --> 00:11:00,900 Compared to the average to change. 173 00:11:00,900 --> 00:11:05,500 Those fluxes to sediment the so-called burial foxes, then the 174 00:11:05,500 --> 00:11:07,800 isotopic. Ratios change. 175 00:11:07,900 --> 00:11:11,900 Some of these mechanisms. I'm referring to can be thought 176 00:11:11,900 --> 00:11:15,300 of as operating within the carbon cycle, such as methane, 177 00:11:15,300 --> 00:11:19,700 clathrates burial is inside. Volcanism is on the other hand 178 00:11:19,700 --> 00:11:22,400 outside the cycle. So, those are set of possible, 179 00:11:22,400 --> 00:11:25,200 external, and intrinsic stressors. 180 00:11:25,700 --> 00:11:29,700 And it's so far as the intrinsic ones go, I tend to think of them 181 00:11:29,700 --> 00:11:33,500 simply as imbalances between respiration and production, you 182 00:11:33,500 --> 00:11:36,100 have the planet wide ratio of carbon 12. 183 00:11:36,300 --> 00:11:40,300 Carbon-13, if you like, then you said, the volcanic ratio is two 184 00:11:40,300 --> 00:11:44,300 bit lighter than that more. C12 is life even more so, and 185 00:11:44,300 --> 00:11:46,900 can you tease apart the various contributions? 186 00:11:47,200 --> 00:11:50,500 Yeah. You can identify various sources 187 00:11:50,500 --> 00:11:54,200 of light, and heavy inputs, but there are n sources of light, 188 00:11:54,200 --> 00:11:56,600 inputs, and M sources of heavy inputs, and n. 189 00:11:56,600 --> 00:11:59,000 And M are large numbers. Then you how can you know, which 190 00:11:59,000 --> 00:12:03,000 ones did it more? Particularly the isotopic 191 00:12:03,000 --> 00:12:07,000 composition of volcanic CO2, it's lighter than An atmospheric 192 00:12:07,000 --> 00:12:10,300 CO2. But it represents the planetary 193 00:12:10,300 --> 00:12:15,200 average because it's basically the CO2 is deeply buried within 194 00:12:15,200 --> 00:12:17,700 your Earth or the carbon is deeply buried in the earth that 195 00:12:17,700 --> 00:12:20,800 comes out as CO2 and it represents the isotopic 196 00:12:20,800 --> 00:12:22,700 composition of carbon in the mountain. 197 00:12:23,000 --> 00:12:27,100 But what happens is it because the carbon cycle photosynthesis 198 00:12:27,100 --> 00:12:31,700 in particular favors, photosynthesis favors the light 199 00:12:31,700 --> 00:12:34,800 isotope, it creates fractionation the difference in 200 00:12:34,800 --> 00:12:39,300 the isotopic. Between light organic carbon and 201 00:12:39,300 --> 00:12:43,500 heavy inorganic carbon. So what did you see when you 202 00:12:43,600 --> 00:12:46,400 plotted these events on a diagram spanning? 203 00:12:46,400 --> 00:12:51,000 The phanerozoic, the most interesting plot takes all of 204 00:12:51,000 --> 00:12:57,100 these events and asks, how do they appear in a plot of the 205 00:12:57,100 --> 00:13:01,000 size of the event versus the time scale at which they occur 206 00:13:01,300 --> 00:13:04,000 timescale being distinct from time? 207 00:13:04,100 --> 00:13:06,100 That is from the date by which they occur. 208 00:13:06,200 --> 00:13:09,000 Heard it's did it occur over a million years over? 209 00:13:09,000 --> 00:13:12,900 100,000 over 10,000 years. When you make such a plot 210 00:13:13,200 --> 00:13:17,400 something interesting is already evident basically see the data 211 00:13:17,400 --> 00:13:20,700 all fall one half of the plot in the other half of the plot is 212 00:13:20,700 --> 00:13:25,100 empty, and divisions of the plot is a diagonal line. 213 00:13:25,400 --> 00:13:28,300 And the diagonal line, you can think of is the rate of change 214 00:13:28,300 --> 00:13:33,600 of the isotope ratios, as a function of the time scale at 215 00:13:33,600 --> 00:13:36,900 which they occur. So, it's a kind of Flux so to 216 00:13:36,900 --> 00:13:40,400 speak and isotopic flux. And what that says and this is 217 00:13:40,400 --> 00:13:42,800 without any kind of interpretation, it's just say, 218 00:13:42,800 --> 00:13:44,800 let's take the data and put it on this plot. 219 00:13:44,900 --> 00:13:48,100 It says that there's this kind of like a speed limit stuff, 220 00:13:48,100 --> 00:13:51,300 can't happen that fast. And the reason the speed limit 221 00:13:51,300 --> 00:13:54,500 is there as because you don't see enormous events and small 222 00:13:54,500 --> 00:13:57,600 amounts of time. What you see, instead is small 223 00:13:57,600 --> 00:14:01,000 events and small amounts of times, the big events take 224 00:14:01,000 --> 00:14:04,500 longer to occur. So I thought that was 225 00:14:04,800 --> 00:14:10,400 interesting And so what I did is try to do something further, 226 00:14:10,400 --> 00:14:15,700 which is to transform this plot and to physical axes. 227 00:14:15,700 --> 00:14:18,700 So that people like us can discuss it and everybody will 228 00:14:18,700 --> 00:14:22,000 understand what's there. And now, the two axes in this 229 00:14:22,000 --> 00:14:25,200 plot, one is still time scale but the other is mass instead of 230 00:14:25,200 --> 00:14:28,100 isotope change. So what is the mass here in 231 00:14:28,100 --> 00:14:30,500 mass? Is the amount of carbon that was 232 00:14:30,500 --> 00:14:33,400 taking part in this isotopic change. 233 00:14:33,400 --> 00:14:38,400 So you integrate the flux, the In flux of carbon, which I think 234 00:14:38,400 --> 00:14:41,500 of as a respiration flocks integrate, that respiration 235 00:14:41,500 --> 00:14:44,100 flock over the time scale and you're going to mass. 236 00:14:44,800 --> 00:14:47,800 And when you make that plot, the something, what in physics? 237 00:14:47,800 --> 00:14:50,800 We will call it data collapse. It's actually quite remarkable 238 00:14:51,400 --> 00:14:55,100 roughly half the data end up falling on a line. 239 00:14:55,600 --> 00:14:57,700 What is that line? That's really interesting. 240 00:14:57,900 --> 00:15:01,000 I called outlying a characteristic rate because it's 241 00:15:01,000 --> 00:15:04,700 the rate of a constant ratio of Mass to timer characteristic 242 00:15:04,700 --> 00:15:07,400 flux so there's this characteristic flux in the 243 00:15:07,408 --> 00:15:10,300 carbon cycle. So that's one interesting thing. 244 00:15:10,600 --> 00:15:15,200 Second interesting thing is that four of the five mass extinction 245 00:15:15,200 --> 00:15:19,100 events, basically, not much else have flux greater than the 246 00:15:19,100 --> 00:15:23,000 characteristic flux. So there are associated with 247 00:15:23,000 --> 00:15:26,600 changes in the carbon cycle that occur at faster than the 248 00:15:26,600 --> 00:15:30,400 characters degree and the extinction event at the end of 249 00:15:30,400 --> 00:15:34,400 the Permian has by far the fastest rate and it stands out 250 00:15:34,400 --> 00:15:38,800 as an extreme outlier this And on the other side of the line 251 00:15:39,100 --> 00:15:42,600 are all the slow events that only Specialists have ever heard 252 00:15:42,600 --> 00:15:45,400 of. And they represent small changes 253 00:15:45,400 --> 00:15:49,700 occurring, longest time scales to be more precise. 254 00:15:49,700 --> 00:15:54,200 They represent low flux offense. I spent quite a bit of time, 255 00:15:54,200 --> 00:15:57,500 trying to figure out what this division of the space means. 256 00:15:58,000 --> 00:15:59,600 Okay? So let's talk about that. 257 00:15:59,900 --> 00:16:02,400 All these events that you analyze during the phanerozoic. 258 00:16:02,400 --> 00:16:04,200 And I believe there were 31 of them. 259 00:16:04,700 --> 00:16:08,800 Most of them actually. Fell near or on this straight 260 00:16:08,800 --> 00:16:12,400 line, which represents a critical rate of change or 261 00:16:12,400 --> 00:16:17,600 critical carbon flux. The criticality of that line is 262 00:16:17,600 --> 00:16:21,600 an interpretation and I'll tell you how I came to that 263 00:16:21,600 --> 00:16:26,200 interpretation as a matter of pure phenomenology, there's a 264 00:16:26,200 --> 00:16:29,300 characteristic flocks or characteristic rate of change. 265 00:16:29,300 --> 00:16:32,700 What could that mean? Well, we talked a little bit 266 00:16:32,700 --> 00:16:36,800 earlier about all the ways in which the isotopic Action of the 267 00:16:36,808 --> 00:16:40,900 carbon cycle could change. And that translates to all the 268 00:16:40,900 --> 00:16:44,100 ways in which the carbon cycle could end up being disrupted. 269 00:16:44,100 --> 00:16:48,600 And we listed a bunch burial changes, methane burps, and 270 00:16:48,700 --> 00:16:52,200 volcanoes becoming anomalously active, and there's a host of 271 00:16:52,200 --> 00:16:55,500 others. If all these things were going 272 00:16:55,500 --> 00:16:59,400 on, some one time another, another time, why would there be 273 00:16:59,400 --> 00:17:02,700 a characteristic rate? Well, I mean there could be but 274 00:17:02,700 --> 00:17:06,000 it doesn't really make sense that so many diverse. 275 00:17:06,099 --> 00:17:08,800 Officers would yield the same characteristic, right? 276 00:17:09,099 --> 00:17:11,800 So the alternative hypothesis is that. 277 00:17:11,900 --> 00:17:15,500 It's the carbon cycle that is changing and it's not really 278 00:17:15,500 --> 00:17:17,599 something outside the carbon cycle. 279 00:17:17,599 --> 00:17:20,500 That's making a change. There may be something outside 280 00:17:20,500 --> 00:17:23,300 the carbon cycle, it instigates the change but then the carbon 281 00:17:23,300 --> 00:17:29,000 cycle then carries on on its own and That's a classic way and 282 00:17:29,000 --> 00:17:33,400 nonlinear physics or nonlinear Dynamics for systems to behave. 283 00:17:33,400 --> 00:17:37,100 You stress them a little bit and then they become come in one 284 00:17:37,100 --> 00:17:41,100 manner or another unstable. And the instability has a 285 00:17:41,100 --> 00:17:45,000 characteristic signature. Maybe the simplest of the 286 00:17:45,000 --> 00:17:48,900 results of such instabilities are non-linear oscillations, in 287 00:17:48,900 --> 00:17:52,700 which there's a system, which goes from being inactive to 288 00:17:52,700 --> 00:17:57,300 oscillating as you often see, when things start to vibrate 289 00:17:57,300 --> 00:17:59,300 because of them. Very stresses that have been 290 00:17:59,300 --> 00:18:01,700 placed on them. And those vibrations have a 291 00:18:01,708 --> 00:18:07,300 typical amplitude and a typical frequency And the hypothesis, I 292 00:18:07,308 --> 00:18:10,500 eventually came to is that what we're seeing for this 293 00:18:10,500 --> 00:18:15,600 characteristic rate is a kind of shadow of that characteristic 294 00:18:15,600 --> 00:18:20,500 oscillation but it's only half a cycle of the oscillation as it 295 00:18:20,500 --> 00:18:23,500 goes up and it comes down and it comes back to where it came 296 00:18:23,500 --> 00:18:26,000 before. And so the question is, how 297 00:18:26,000 --> 00:18:29,200 could that happen? Then the theory of dynamical 298 00:18:29,200 --> 00:18:32,400 systems. This is a well-known scenario 299 00:18:32,400 --> 00:18:34,900 and such systems are called excitable. 300 00:18:35,000 --> 00:18:38,600 Well, they're actually from a dynamical point of view always 301 00:18:38,600 --> 00:18:44,600 stable, but if you stress them sufficiently but not that much. 302 00:18:44,700 --> 00:18:48,500 They act as if they're going unstable and they do that only 303 00:18:48,500 --> 00:18:51,600 for the equivalent of one cycle. And then they return back to the 304 00:18:51,600 --> 00:18:57,000 stable equilibrium excitable systems were first studied in 305 00:18:57,000 --> 00:19:01,500 Neuroscience, because this is how neurons work or sometimes 306 00:19:01,500 --> 00:19:04,900 it's called Action. Potentials you inject a small? 307 00:19:05,100 --> 00:19:07,700 I went into a neuron and if it goes above a threshold, in a 308 00:19:07,708 --> 00:19:10,200 fire's appals, his pulse is called a spike. 309 00:19:10,200 --> 00:19:12,900 This is how the brain works. For example, that's fascinating. 310 00:19:12,900 --> 00:19:18,800 So they could be this dynamical system that maybe underlies the 311 00:19:18,800 --> 00:19:23,700 carbon cycle, you stress it and it gets excited and does one 312 00:19:23,800 --> 00:19:27,300 Excursion, which then is one of the things you pick up with your 313 00:19:27,300 --> 00:19:30,400 spike in the isotope ratio and then it goes back more or less 314 00:19:30,400 --> 00:19:34,900 to where it was before, right? Looks just like an excitation. 315 00:19:35,000 --> 00:19:37,800 Ation. And so this is an example of 316 00:19:37,800 --> 00:19:40,800 what people these days refer to as tipping phenomenon or a 317 00:19:40,800 --> 00:19:43,600 Tipping Point. This is a particularly 318 00:19:43,700 --> 00:19:46,700 interesting kind of Tipping Point in which we're not 319 00:19:46,700 --> 00:19:50,400 Crossing change of state boundary phase transitions. 320 00:19:50,800 --> 00:19:54,900 Instead, what we're doing is changing a parameter in such a 321 00:19:54,900 --> 00:19:59,000 way that it acts as if across the boundary but then it comes 322 00:19:59,000 --> 00:20:02,800 back to where it was. And with all these events that 323 00:20:02,800 --> 00:20:09,000 you looked at you said, four The five big five extinctions, well, 324 00:20:09,000 --> 00:20:13,100 above this line, which you interpret is a critical rate. 325 00:20:13,300 --> 00:20:17,400 So is there something different there, that pushes them even 326 00:20:17,400 --> 00:20:19,900 beyond what the carbon cycle would go to? 327 00:20:20,300 --> 00:20:25,600 The idea is that most of us represent some type of modest 328 00:20:25,600 --> 00:20:28,700 dress, which that is expressed by the internal dynamics of the 329 00:20:28,700 --> 00:20:30,600 carbon cycle. That's a hypothesis. 330 00:20:30,600 --> 00:20:32,200 That explains the characteristic. 331 00:20:32,200 --> 00:20:36,200 Great. Now why are Sections above it. 332 00:20:36,400 --> 00:20:40,400 I would qualify your statement a little bit more and say one is 333 00:20:40,400 --> 00:20:42,700 unequivocally above the characteristic, right? 334 00:20:42,700 --> 00:20:45,800 That's the end-permian extinction, three of them, 335 00:20:46,700 --> 00:20:50,200 probably about it and what makes them special? 336 00:20:50,300 --> 00:20:54,700 This is a great question. I say that they represent 337 00:20:54,700 --> 00:20:57,300 excitations that have been stressed, well, beyond the 338 00:20:57,300 --> 00:21:01,500 threshold, the excitation parameter is rate of change of 339 00:21:01,500 --> 00:21:04,900 CO2. If we put CO2 into this system, 340 00:21:05,000 --> 00:21:09,400 Them sufficiently fast than the carbon cycle. 341 00:21:09,500 --> 00:21:13,600 Fires a kind of acidification pulse, which is a change in the 342 00:21:13,600 --> 00:21:19,600 CO2 content of the oceans. If we do that in a way, that is 343 00:21:19,700 --> 00:21:23,900 well beyond threshold, or the carbon cycle has some special 344 00:21:23,900 --> 00:21:26,600 Dynamics to take into another region. 345 00:21:26,600 --> 00:21:29,900 Then the result can be something that's effectively greater than 346 00:21:29,900 --> 00:21:33,100 or worse than the typical spiking event. 347 00:21:33,300 --> 00:21:36,500 It's a kind of grow since Ability as opposed to the 348 00:21:36,500 --> 00:21:42,500 generic one, I don't really have a new theory of mass extinction 349 00:21:42,500 --> 00:21:45,700 instead. What I am suggesting is that the 350 00:21:45,700 --> 00:21:52,400 carbon cycle acts in association with mass extinctions, I can't 351 00:21:52,400 --> 00:21:54,800 show that it causes the mass extinction. 352 00:21:54,900 --> 00:21:57,800 I can't show that mass extinction caused the changes in 353 00:21:57,800 --> 00:21:59,900 the carbon cycle. Instead, what I can clearly 354 00:21:59,900 --> 00:22:04,800 point to is that there's an association that are and that 355 00:22:05,000 --> 00:22:08,400 This is Association is particularly pronounced and the 356 00:22:08,400 --> 00:22:11,800 cases of the worst mass extinctions, the four of the big 357 00:22:11,800 --> 00:22:15,300 five. The curiosity is that there's a 358 00:22:15,300 --> 00:22:18,500 whole bunch of other events, the ones I've studied, which you 359 00:22:18,500 --> 00:22:21,900 might call them paleo climate events but not times of great 360 00:22:21,900 --> 00:22:23,200 biotic. Turnover. 361 00:22:24,500 --> 00:22:27,600 And there are significant disruptions by themselves. 362 00:22:28,000 --> 00:22:32,100 And there's a very interesting question is to what makes them 363 00:22:32,100 --> 00:22:34,400 different. Why aren't they mass extinction 364 00:22:34,400 --> 00:22:37,300 grade? Wait, well, this study I did. 365 00:22:37,300 --> 00:22:40,400 I basically undertook to try to address that question so I can 366 00:22:40,400 --> 00:22:44,400 separate them in this space. I can answer your question by 367 00:22:44,400 --> 00:22:47,400 saying extinctions or Worse, their excite-ation is pushed, 368 00:22:47,400 --> 00:22:50,400 well beyond the threshold but there's a lot of questions that 369 00:22:50,400 --> 00:22:52,900 remain unanswered just to come back to the underlying 370 00:22:52,900 --> 00:22:55,200 mechanisms again. So when you have one of these 371 00:22:55,200 --> 00:22:59,600 events that put you on this excursion, if you like to the 372 00:22:59,600 --> 00:23:03,000 spike and then back again, do we have hypotheses as to what the 373 00:23:03,000 --> 00:23:05,800 underlying chemistry? Oh, Biochemistry. 374 00:23:05,800 --> 00:23:09,900 Is that first allows the Excursion at the characteristic 375 00:23:09,900 --> 00:23:13,100 great and then brings it back down to where it was, that's a 376 00:23:13,108 --> 00:23:16,600 good question. Any system that undergoes some 377 00:23:16,600 --> 00:23:21,000 type of instability, can't stay unstable forever. 378 00:23:21,000 --> 00:23:23,700 It is essentially my say, it Peters out. 379 00:23:23,700 --> 00:23:26,200 Why does it do that? Is because there is always some 380 00:23:26,200 --> 00:23:31,200 mechanism of dissipation. Something that slows it down and 381 00:23:31,500 --> 00:23:34,400 insofar as carbon cycle disruptions go. 382 00:23:34,400 --> 00:23:39,200 There's a A well-studied mechanism that slows down and 383 00:23:39,200 --> 00:23:43,500 dampens out any kind of acidification Spike or Symbian 384 00:23:43,500 --> 00:23:45,800 injection of CO2 into the oceans. 385 00:23:46,400 --> 00:23:50,700 And that mechanism is sometimes referred to as carbonate, 386 00:23:50,700 --> 00:23:55,800 compensation or sometimes referred to as the homeostatic 387 00:23:55,800 --> 00:23:58,300 response of the oceans carbonate system. 388 00:23:59,000 --> 00:24:02,400 At least, since the Triassic there, have been lots of shells, 389 00:24:02,400 --> 00:24:07,100 littering the seafloor, which contain Minerals these carbonate 390 00:24:07,100 --> 00:24:10,700 minerals, when they are dissolved by the acidic Waters 391 00:24:10,700 --> 00:24:14,200 act to lower the ph. It's sometimes said that the 392 00:24:14,200 --> 00:24:17,400 carbonate minerals at the bottom of the sea floor, sort of like 393 00:24:17,400 --> 00:24:20,900 the oceans and acid pills that you might take when you have an 394 00:24:20,900 --> 00:24:25,200 acidic stomach, they act to neutralize the pH because 395 00:24:25,200 --> 00:24:30,400 they're being dissolved and that is thought to play out today. 396 00:24:30,800 --> 00:24:35,200 Roughly 10,000 year, timescale, that time scale was Probably 397 00:24:35,200 --> 00:24:37,900 longer in the past. And would that be because of 398 00:24:37,900 --> 00:24:43,300 evolution of these calcareous microorganisms, precisely, the 399 00:24:43,300 --> 00:24:47,500 invention of calcifying photosynthesizers, which created 400 00:24:47,500 --> 00:24:51,700 was sometimes referred to as a deep-sea carbonate sink acts as 401 00:24:51,700 --> 00:24:56,200 a stabilizing mechanism and the carbon cycle, the more carbonate 402 00:24:56,200 --> 00:24:59,700 shells, there are in the sea floor, the easier it is to 403 00:24:59,700 --> 00:25:02,700 dissolve these anti-acid pills on the bottom of the sea. 404 00:25:02,900 --> 00:25:04,800 The easier it is to neutralize the event. 405 00:25:05,000 --> 00:25:08,000 Shorter the time scale. It's a very interesting way in 406 00:25:08,000 --> 00:25:11,100 which nature and maintains or tries to maintain equilibrium 407 00:25:11,100 --> 00:25:14,200 and the carbon cycle, the final element of the story is that 408 00:25:14,200 --> 00:25:17,300 there's always dissolved calcium carbonate coming into this 409 00:25:17,300 --> 00:25:21,700 oceans via rivers and it's going out by a burial and rocks and 410 00:25:21,700 --> 00:25:24,400 simply by flushing out the system at long timescales. 411 00:25:24,400 --> 00:25:28,000 You also tend to dampen it out. So you talked about the 412 00:25:28,000 --> 00:25:31,600 homeostatic timescale being about 10,000 years for the 413 00:25:31,600 --> 00:25:34,800 modern ocean. So that's the time scale, if you 414 00:25:34,900 --> 00:25:40,700 Like it takes for these non equilibrium processes to Peak 415 00:25:40,700 --> 00:25:42,800 and damp out. Yes. 416 00:25:42,800 --> 00:25:47,400 Because first approximation the damping time scale is also the 417 00:25:47,400 --> 00:25:50,400 time scale, it takes to reach Peak disturbance. 418 00:25:50,800 --> 00:25:55,500 So now I'd like to see if your way of approaching this problem 419 00:25:55,500 --> 00:26:00,100 enables us to connect the events that you see in the geological 420 00:26:00,100 --> 00:26:05,800 record for which, you know, the size and the duration to Events 421 00:26:06,300 --> 00:26:09,900 that disrupt the carbon cycle on a much shorter time scale. 422 00:26:10,400 --> 00:26:14,800 We have these events in geologic history that a current long 423 00:26:14,800 --> 00:26:17,400 time. Scales tens of thousands, 424 00:26:17,400 --> 00:26:21,000 hundreds of thousands sometimes millions of years and we have an 425 00:26:21,000 --> 00:26:24,300 event today, which is basically is crying at a century time 426 00:26:24,300 --> 00:26:27,000 scale, fossil fuel burning injection of CO2 in the 427 00:26:27,000 --> 00:26:31,300 atmosphere and so it's reasonable to think that one has 428 00:26:31,300 --> 00:26:34,600 nothing to do with the other, but that can't really be true. 429 00:26:34,600 --> 00:26:37,200 There are Things you can learn from how the Earth system, the 430 00:26:37,200 --> 00:26:42,100 carbon cycle behave in the past. So what I tried to do here show 431 00:26:42,100 --> 00:26:44,700 what can be done in a quantitative way. 432 00:26:45,400 --> 00:26:50,600 What we see in the data is this characteristic rate, this 433 00:26:50,600 --> 00:26:56,500 characteristic rate provides a very interesting quantities says 434 00:26:56,500 --> 00:27:00,600 that if things long time scales are stressed, if carbon is 435 00:27:00,600 --> 00:27:04,200 injected into the system faster than the characteristic rate, 436 00:27:04,400 --> 00:27:08,800 then we Serious disruption events at the same time as you 437 00:27:08,800 --> 00:27:11,000 already indicated in your question. 438 00:27:11,000 --> 00:27:12,900 There's also a damping mechanism. 439 00:27:13,300 --> 00:27:17,700 So it was a damping mechanism and a characteristic rate and so 440 00:27:17,700 --> 00:27:20,900 characteristic rate times a damping mechanism gives you a 441 00:27:20,900 --> 00:27:24,400 mass or critical rate I should say because we take the 442 00:27:24,400 --> 00:27:28,300 characters to create as an upper bound on the critical rate, it 443 00:27:28,300 --> 00:27:31,200 gives you a critical mass. Now, why is that? 444 00:27:31,400 --> 00:27:37,200 And for that, I mostly appeal to a Observation, this podcast has 445 00:27:37,200 --> 00:27:39,000 been going on. Now, I'm not quite sure what it 446 00:27:39,000 --> 00:27:41,800 will be after you edit it, but, you know, order, 30 minutes, 447 00:27:42,500 --> 00:27:44,900 most people are probably listening to it inside and 448 00:27:44,900 --> 00:27:49,300 outside let's say the CO2 levels went up 1 or 2 PPM during the 449 00:27:49,300 --> 00:27:52,500 podcast. Nobody there's not a single 450 00:27:52,500 --> 00:27:55,900 organism on the planet that will notice all right. 451 00:27:56,100 --> 00:27:59,200 But it's rate of change will have been effectively infinite 452 00:27:59,200 --> 00:28:02,700 or at least very, very large impulse or Delta function. 453 00:28:03,700 --> 00:28:10,200 So You see right away that this idea of rates matter is kind of 454 00:28:10,600 --> 00:28:13,500 limited in its applicability because you know here we have an 455 00:28:13,500 --> 00:28:14,900 infinite right nothing's going on. 456 00:28:15,700 --> 00:28:22,300 So what that means is that at the short time scale it's the 457 00:28:22,300 --> 00:28:26,300 amount by which the system changes but it's the long time 458 00:28:26,300 --> 00:28:29,100 scale. It's the rate at which it 459 00:28:29,100 --> 00:28:34,800 changes and the way you can get the critical mass from the 460 00:28:34,900 --> 00:28:38,600 critical rate is to multiply the critical rate by the damping 461 00:28:38,600 --> 00:28:44,000 time scale and the product of those two because of the type of 462 00:28:44,000 --> 00:28:46,700 relaxation mechanisms that talked about will give you the 463 00:28:46,700 --> 00:28:52,600 critical mass and that then gives rise to a prediction we 464 00:28:52,600 --> 00:28:54,900 can calculate this critical mass. 465 00:28:55,300 --> 00:28:58,300 It's basically the mass that you would inject into the carbon 466 00:28:58,300 --> 00:29:01,600 cycle over the typical damping time scale in this case today is 467 00:29:01,600 --> 00:29:04,200 10,000 years. So we know that the critical 468 00:29:04,600 --> 00:29:09,300 radius It is a few hundreds of a giga ton of carbon per year. 469 00:29:09,300 --> 00:29:13,700 You multiply it by 100 years and you get a number that's on your 470 00:29:13,700 --> 00:29:16,800 order of three or four hundred gigatons of carbon into the 471 00:29:16,800 --> 00:29:20,200 oceans. And I believe we've put in about 472 00:29:20,200 --> 00:29:24,000 200 Giga, tons. If you look at projections from 473 00:29:24,000 --> 00:29:27,000 things like the ipcc report, what you can see is we will have 474 00:29:27,300 --> 00:29:30,000 three or four hundred gigatons of carbon into the system, you 475 00:29:30,008 --> 00:29:33,900 know, probably sometime before the end of this century is three 476 00:29:33,900 --> 00:29:36,800 or 400 gigaton. Runs into the surface ocean and 477 00:29:36,800 --> 00:29:42,600 so that suggests that if we stay on the present path but if it 478 00:29:42,600 --> 00:29:47,700 gets over a certain amount then an instability might begin and 479 00:29:47,700 --> 00:29:52,300 that instability is not instantaneous and so far as my 480 00:29:52,300 --> 00:29:56,000 own work goes it would predicted a plays out over time scale 481 00:29:56,200 --> 00:29:58,900 which is equivalent to the damping time scale, which is 482 00:29:58,900 --> 00:30:01,500 10,000 years. So it's not something that 483 00:30:01,600 --> 00:30:03,900 necessarily need to worry about the moment. 484 00:30:03,900 --> 00:30:08,700 What this is They saying is that there's a very logical rational 485 00:30:08,700 --> 00:30:13,800 way of looking at past carbon cycle events, and from them 486 00:30:13,800 --> 00:30:18,300 being able to infer how much CO2 is too much and so far as the 487 00:30:18,300 --> 00:30:24,000 future of life on Earth cars and result of this analysis, is that 488 00:30:24,000 --> 00:30:27,600 anything that we can do to slow the injection of CO2 in the 489 00:30:27,600 --> 00:30:30,600 atmosphere May pay out at a very long time, scale. 490 00:30:31,100 --> 00:30:33,800 It's really intriguing. How you managed to connect a 491 00:30:33,800 --> 00:30:36,700 short impulses? If you like that's driven by 492 00:30:36,700 --> 00:30:41,400 anthropogenic fossil fuel burning with the geological 493 00:30:41,400 --> 00:30:43,100 events that we see in the record. 494 00:30:43,100 --> 00:30:47,600 So you mentioned a critical mass of something on the order of 300 495 00:30:47,600 --> 00:30:51,000 gigatons. Are you able to figure out how 496 00:30:51,000 --> 00:30:53,400 much carbon was injected into the system? 497 00:30:53,400 --> 00:30:57,200 Say at the end of the Cretaceous, when the dinosaurs 498 00:30:57,200 --> 00:31:02,500 died out the best work in that regard is done by some Geo 499 00:31:02,500 --> 00:31:05,700 chronologiste at. Princeton that have Carefully 500 00:31:05,700 --> 00:31:09,700 dated the magmatic deposits coming from massive, volcanism 501 00:31:09,700 --> 00:31:14,400 in the Deccan traps in India, just before the and Cretaceous 502 00:31:14,400 --> 00:31:17,500 event. Now, most people listening to 503 00:31:17,500 --> 00:31:20,100 this will know the and Cretaceous event is the event 504 00:31:20,100 --> 00:31:23,200 that was the demise of the dinosaurs, and everyone is 505 00:31:23,200 --> 00:31:26,000 taught that, that's a result of an impact with an 506 00:31:26,000 --> 00:31:29,900 extraterrestrial object, a bolide or meteor impact. 507 00:31:29,900 --> 00:31:34,700 However, if you dig into it more deeply, it's also now well, 508 00:31:34,800 --> 00:31:39,600 Guys, that was massive volcanism occurring at the same time and 509 00:31:39,600 --> 00:31:43,800 the best geochronology shows unequivocally that the massive 510 00:31:43,800 --> 00:31:46,900 volcanism was going on during this period. 511 00:31:46,900 --> 00:31:52,700 Moreover, there's a significant pulse is not uniform in time, 512 00:31:52,800 --> 00:31:57,800 but there's a pulse 10,000 years before the and Cretaceous event. 513 00:31:57,800 --> 00:32:03,400 Now, no one's denying that the impact itself had some effect. 514 00:32:03,400 --> 00:32:07,300 But now you've seen it, there's Pulse of volcanic CO2 going into 515 00:32:07,300 --> 00:32:11,300 the system 10,000 years before. I know, is it this 10,000-year 516 00:32:11,300 --> 00:32:15,100 number kind of interesting I thought alright because that's 517 00:32:15,100 --> 00:32:17,800 the time it takes for the types of excitations. 518 00:32:17,800 --> 00:32:22,100 I'm talking about to reach their worst or most severe limit and 519 00:32:22,100 --> 00:32:27,900 so what you can do is put this data point on the type of plot 520 00:32:27,900 --> 00:32:32,600 on talking about and on this plot we have the time scale of 521 00:32:32,600 --> 00:32:35,900 the event and the side. Size of the event. 522 00:32:36,500 --> 00:32:43,600 What such a plot shows is that both the magnetic flux pulse 523 00:32:43,700 --> 00:32:48,800 which produces CO2 just before the and Cretaceous event and 524 00:32:48,900 --> 00:32:53,300 current injection of CO2 in the atmosphere, basically exists 525 00:32:53,300 --> 00:32:57,400 near the critical rate. Now, I should qualify that 526 00:32:57,400 --> 00:33:00,800 because the critical rate is different in the case of the 527 00:33:00,800 --> 00:33:03,900 Cretaceous event and modern disruption. 528 00:33:04,800 --> 00:33:08,700 I spoke earlier of a critical mass but if we divide that 529 00:33:08,700 --> 00:33:12,900 critical mass by the time scale which is injected into the 530 00:33:12,900 --> 00:33:17,200 oceans, we get another rate. It turns out that because there 531 00:33:17,200 --> 00:33:21,500 is a critical mass. The the shorter the time scale 532 00:33:21,500 --> 00:33:26,100 of the injection, the larger is the critical rate a short time 533 00:33:26,100 --> 00:33:28,200 scales. So there's basically what we 534 00:33:28,200 --> 00:33:30,700 call scaling law that one can derive from this. 535 00:33:31,100 --> 00:33:32,800 It says that it's short time scales. 536 00:33:32,800 --> 00:33:35,400 There's not only critical mass but the critical No, Mass can be 537 00:33:35,400 --> 00:33:40,000 reinterpreted as a critical rate that depends on the timescale. 538 00:33:40,500 --> 00:33:46,000 The critical rate today is 100 times greater than the critical 539 00:33:46,000 --> 00:33:49,100 rate in the Cretaceous and that's because this Cretaceous 540 00:33:49,100 --> 00:33:50,800 event. I'm talking about plays out over 541 00:33:50,800 --> 00:33:53,600 10,000 years. Or as today's event is 542 00:33:53,600 --> 00:33:56,500 occurring, over a hundred years, there's a two orders of 543 00:33:56,500 --> 00:34:01,000 magnitude and the rate. And it's interesting to note 544 00:34:01,100 --> 00:34:04,700 that yes, of course, the current event. 545 00:34:04,900 --> 00:34:08,400 Is a rate, which is 100 times faster and that's alarming by 546 00:34:08,400 --> 00:34:12,000 itself, but it turns out that if you analyze it carefully, they 547 00:34:12,000 --> 00:34:16,000 both fall on our rescaled critical rate line, in other 548 00:34:16,000 --> 00:34:20,699 words in so far as the mass extinction risk is concerned, 549 00:34:20,800 --> 00:34:24,300 both The Modern event and the and Cretaceous event appeared to 550 00:34:24,300 --> 00:34:28,400 be near the critical rate. Even though the modern event as 551 00:34:28,400 --> 00:34:30,400 a rate, which is 100 times faster. 552 00:34:31,000 --> 00:34:32,800 So that's a pretty alarming conclusion. 553 00:34:32,800 --> 00:34:36,199 That basically says that Whatever created the mass 554 00:34:36,199 --> 00:34:40,199 extinction at the end of the Cretaceous was caused in some 555 00:34:40,199 --> 00:34:44,100 way that you've now shown by an equivalent amount of disruption 556 00:34:44,100 --> 00:34:47,800 to the carbon cycle in terms of its destructive potential. 557 00:34:48,600 --> 00:34:51,900 How solid is the reasoning that led you to this conclusion? 558 00:34:51,900 --> 00:34:55,800 Do you think the reasoning is solid within the data that we 559 00:34:55,800 --> 00:34:58,800 have? But the most important thing 560 00:34:58,800 --> 00:35:03,100 that's missing is an understanding of the negative 561 00:35:03,100 --> 00:35:07,700 feedbacks that might occur. Are largely due to changes in 562 00:35:07,700 --> 00:35:11,800 ecology or ocean ecology or ocean biology for that matter. 563 00:35:12,000 --> 00:35:16,500 Over the course of the 10,000 years, which in the modern case, 564 00:35:16,500 --> 00:35:19,300 if we disrupt it beyond the threshold, what's going to 565 00:35:19,300 --> 00:35:23,800 happen? It may want to go off onto a 566 00:35:23,800 --> 00:35:25,800 trajectory that would be unstable. 567 00:35:26,000 --> 00:35:29,800 If the only thing that were governing the Dynamics, where 568 00:35:29,800 --> 00:35:32,200 the long time scales, that is the Thousand Year. 569 00:35:32,200 --> 00:35:36,400 Timescale controls on the dynamical, Adam, however, the 570 00:35:36,400 --> 00:35:40,100 our system varies at a great deal of time scales, and it may 571 00:35:40,100 --> 00:35:43,400 be that there are negative feedback so that occur at 572 00:35:43,400 --> 00:35:45,600 Century timescales decade of time scales. 573 00:35:45,600 --> 00:35:48,800 And so, on that act down this out, we don't know. 574 00:35:49,100 --> 00:35:55,400 But the conclusion I'm drawing is absolutely solid on physical 575 00:35:55,400 --> 00:35:58,300 grounds. Given the available data. 576 00:35:58,300 --> 00:36:02,200 It's basically an attempt to say we have these observations. 577 00:36:02,200 --> 00:36:06,600 What can we conclude from them? Using Elementary physical 578 00:36:06,600 --> 00:36:10,400 intuition, and an understanding of what isotopic changes mean. 579 00:36:10,800 --> 00:36:14,200 So what father worker observations, would you like to 580 00:36:14,200 --> 00:36:18,900 see to test these ideas further and constrain the predictions a 581 00:36:18,900 --> 00:36:22,600 little bit more? Any kind of data that allows us 582 00:36:22,600 --> 00:36:26,300 to see stimuli distinct from responses? 583 00:36:26,300 --> 00:36:28,500 Would help? And that's a difficult problem 584 00:36:28,500 --> 00:36:33,000 because in geology, we usually have one window with which to 585 00:36:33,000 --> 00:36:36,000 look at things and it contains both the record of the stimulus 586 00:36:36,000 --> 00:36:38,000 and the response. So that would be something that 587 00:36:38,000 --> 00:36:41,200 would maybe take us beyond the carbon cycle to look at other 588 00:36:41,200 --> 00:36:44,500 Isotopes. Other Isotopes changes and 589 00:36:44,500 --> 00:36:49,300 biomarkers organic changes the whole nine yards, so to speak 590 00:36:49,300 --> 00:36:53,400 the whole periodic table. And you know, fossil changes 591 00:36:53,400 --> 00:36:57,600 here basically what geochemists and paleontologist already do 592 00:36:57,800 --> 00:37:01,900 but focused on the events themselves. 593 00:37:02,000 --> 00:37:05,400 These periods of disruption. Dan Rothman. 594 00:37:05,400 --> 00:37:09,300 Thank you very much, thank you. Oliver been a pleasure for more 595 00:37:09,300 --> 00:37:13,400 about geology b, as well as pictures and illustrations, that 596 00:37:13,400 --> 00:37:16,700 support this podcast, go to geology B.com.