WEBVTT 1 00:00:03.439 --> 00:00:07.719 Welcome to Bedtime Astronomy. Explore the wonders of the cosmos 2 00:00:07.759 --> 00:00:12.279 with our soothing Bedtime Astronomy podcast. Each episode offers a 3 00:00:12.359 --> 00:00:16.320 gentle journey through the stars, planets, and beyond, perfect for 4 00:00:16.399 --> 00:00:20.239 unwinding after a long day. Let's travel through the mysteries 5 00:00:20.239 --> 00:00:22.440 of the universe as you drift off into a peaceful 6 00:00:22.480 --> 00:00:26.760 slumber under the night sky. 7 00:00:26.960 --> 00:00:30.719 Welcome everyone. Today, we are doing a deep dive into well, 8 00:00:30.800 --> 00:00:32.560 one of the biggest mysteries out there about our own 9 00:00:32.560 --> 00:00:35.759 planet's history. It's a real cold case, it really is. 10 00:00:35.880 --> 00:00:39.960 We're talking about the moment Earth fundamentally started to breathe, 11 00:00:40.320 --> 00:00:44.520 the event that really set the stage for all complex life. 12 00:00:44.600 --> 00:00:48.119 For us, the Great oxidation event. Yeah, the goe and Yeah. 13 00:00:48.159 --> 00:00:52.600 The scale of this change is it's hard to overstate, 14 00:00:52.679 --> 00:00:55.679 really billions of years where Earth was basically an oxygen 15 00:00:55.759 --> 00:00:57.280 free zone, reducing. 16 00:00:56.880 --> 00:00:59.640 World holding its breath as you put it, Yeah, exactly. 17 00:01:00.280 --> 00:01:02.679 Then some are around two point one to two point 18 00:01:02.679 --> 00:01:06.920 four billion years ago, things flipped dramatically. Suddenly there's this 19 00:01:07.120 --> 00:01:08.799 massive release of oxygen into. 20 00:01:08.640 --> 00:01:10.760 The atmosphere, changing everything forever. 21 00:01:10.959 --> 00:01:13.920 Absolutely. But here's the kicker, The big puzzle scientists have 22 00:01:14.000 --> 00:01:17.480 wrestled with. Right, the microbes responsible, these tiny little things 23 00:01:17.519 --> 00:01:21.319 called cyanobacteria. They figured out how to make oxygen way 24 00:01:21.359 --> 00:01:23.040 way before the goe actually. 25 00:01:22.840 --> 00:01:25.239 Happened, hundreds of millions of years earlier. Right, that's the 26 00:01:25.280 --> 00:01:25.920 baffling part. 27 00:01:26.040 --> 00:01:28.760 Could be three hundred maybe even five hundred million years. 28 00:01:29.239 --> 00:01:33.159 Think about that gap, it's enormous. You've got the oxygen factories, 29 00:01:33.200 --> 00:01:37.120 they're built, they're running, technically capable of pumping out oxygen, but. 30 00:01:37.079 --> 00:01:40.879 The atmosphere isn't changing. The lights are off globally speaking. 31 00:01:40.959 --> 00:01:45.120 So the question's always been why why the huge delay? 32 00:01:45.280 --> 00:01:47.879 Yeah, if the generators were online, what was stopping the 33 00:01:47.920 --> 00:01:49.000 grid from powering up? 34 00:01:49.079 --> 00:01:49.439 Mm hmm. 35 00:01:49.719 --> 00:01:52.640 There have been theories, of course, good ones like volcanic 36 00:01:52.719 --> 00:01:56.400 gases just sucking up all the oxygen or other microbes 37 00:01:56.439 --> 00:01:57.480 eating it exactly. 38 00:01:57.560 --> 00:02:00.200 Those are definitely part of the picture, but they they 39 00:02:00.200 --> 00:02:04.920 never quite seemed to fully explain that incredibly long, stable 40 00:02:04.959 --> 00:02:07.879 delay and then the sudden shift. It felt like something 41 00:02:07.959 --> 00:02:08.800 was missing. 42 00:02:08.560 --> 00:02:09.639 A bottleneck somewhere. 43 00:02:09.680 --> 00:02:12.599 A bottleneck. Yeah, And that's where this new research comes in. 44 00:02:12.680 --> 00:02:16.000 It's work out of Okayami University, led by doctor Dylan Retnayek, 45 00:02:16.159 --> 00:02:18.599 published recently, they took a different angle. Instead of just 46 00:02:18.840 --> 00:02:21.639 the big planetary sinks, they looked smaller exactly. 47 00:02:21.719 --> 00:02:25.080 They zoomed right in on the microscopic level, the ecological factors. 48 00:02:25.360 --> 00:02:28.800 What was actually controlling the growth of the cyanobacteria themselves? 49 00:02:29.280 --> 00:02:33.000 Could they thrive or were they just sort of sputtering along? 50 00:02:33.080 --> 00:02:37.080 Okay, So finding the precise control knob at the microbial level. 51 00:02:36.960 --> 00:02:40.319 That's the idea, and their research points to two maybe 52 00:02:40.319 --> 00:02:43.840 surprisingly simple compounds, nickel and urea. 53 00:02:44.000 --> 00:02:46.120 Nickel and urea, Okay, that's not what usually comes to 54 00:02:46.159 --> 00:02:47.919 mind with planet scale changes. 55 00:02:47.759 --> 00:02:50.639 Right, but this study suggests they were the keys, first 56 00:02:50.680 --> 00:02:54.039 locking the oxygen supply down and then eventually unlocking it. 57 00:02:54.199 --> 00:02:55.960 So that's our mission for this deep dive. We're going 58 00:02:56.000 --> 00:02:58.960 to unpack exactly how nickel and urea could have acted 59 00:02:59.039 --> 00:03:03.199 as this biogeochemical bottleneck. We want to give you that 60 00:03:03.240 --> 00:03:06.520 aha moment connecting the dots between tiny microbes and the 61 00:03:06.560 --> 00:03:09.199 whole planet's atmosphere. Let's get into it, Okay, So let's 62 00:03:09.240 --> 00:03:12.400 set the stage properly. Section one, the Great oxidation delay. 63 00:03:12.759 --> 00:03:15.319 We need to appreciate just how big a deal the 64 00:03:15.360 --> 00:03:16.120 GOE was. 65 00:03:16.439 --> 00:03:20.159 It's truly a fundamental turning point. Before the goe. You've 66 00:03:20.199 --> 00:03:23.479 got what's called a reducing atmosphere. I think lots of 67 00:03:23.560 --> 00:03:28.439 compounds that readily react with oxygen, reduced iron, sulfur, methane, 68 00:03:28.840 --> 00:03:30.319 things like that dominated. 69 00:03:30.439 --> 00:03:32.439 So any free oxygen that popped up would just get 70 00:03:32.479 --> 00:03:35.400 instantly consumed by the surrounding chemistry pretty much. 71 00:03:35.439 --> 00:03:38.719 Yeah, the environment had a huge capacity to soak it up, 72 00:03:38.960 --> 00:03:41.879 and when oxygen did start to build up significantly, it 73 00:03:41.960 --> 00:03:45.520 was actually well toxic, a crisis for much of the 74 00:03:45.560 --> 00:03:48.919 life that existed back then, which was anaerobic didn't use oxygen. 75 00:03:49.039 --> 00:03:50.919 Right, Oxygen was poisonous to early life. 76 00:03:51.000 --> 00:03:53.879 It's ironic, it is, But it was this very crisis, 77 00:03:53.919 --> 00:03:57.840 this environmental shift, that ultimately paved the way for us 78 00:03:58.240 --> 00:04:02.280 for complex multicellular life that needs oxygen. This transition marks 79 00:04:02.280 --> 00:04:05.520 the boundary between the Rchean and Proterozoic eons roughly two 80 00:04:05.599 --> 00:04:07.240 point four billion years ago. 81 00:04:07.120 --> 00:04:09.360 And the agents of this change, the little heroes or 82 00:04:09.400 --> 00:04:13.800 villains depending on your perspective, back then, were the cyanobacteria. 83 00:04:13.000 --> 00:04:18.040 These incredible microbes. They perform oxygenic photosynthesis. Basically, they take sunlight, 84 00:04:18.360 --> 00:04:21.000 water CO two stuff that's everywhere and turn it into 85 00:04:21.079 --> 00:04:21.519 energy for. 86 00:04:21.480 --> 00:04:23.959 Themselves, and oxygen is the waste product. 87 00:04:24.040 --> 00:04:27.480 Oxygen is the exhaust. Exactly a revolutionary invention. 88 00:04:27.279 --> 00:04:30.800 But an invention that, based on genetic evidence, seems to 89 00:04:30.879 --> 00:04:33.600 pre date the GOE by a massive margin. 90 00:04:33.720 --> 00:04:33.920 Yeah. 91 00:04:33.959 --> 00:04:36.720 The molecular clock studies looking at the genes of modern 92 00:04:36.759 --> 00:04:40.839 cyanobacteria and tracing them back strongly suggests the evolution of 93 00:04:40.879 --> 00:04:44.560 this process happened maybe three hundred maybe five hundred million 94 00:04:44.639 --> 00:04:48.000 years before the atmosphere actually registered it. The tech was there, 95 00:04:48.399 --> 00:04:49.439 the impact wasn't. 96 00:04:49.759 --> 00:04:52.279 So let's revisit those earlier theories for the delay. You 97 00:04:52.360 --> 00:04:53.839 mentioned the big sinks, right. 98 00:04:54.399 --> 00:04:58.800 Traditionally the thinking focused on these massive planetary buffers. One 99 00:04:58.959 --> 00:05:03.480 was geological vultvolcanic activity. Early Earth was much more volcanically active, 100 00:05:03.519 --> 00:05:08.000 pumping out loads of producing gases hydrogen, sulfur, dioxide. 101 00:05:07.519 --> 00:05:10.079 Methane, gasses that just react instantly with O two. 102 00:05:10.160 --> 00:05:13.279 Instantly, So it's like a giant geological vacuum cleaner constantly 103 00:05:13.319 --> 00:05:16.519 running sucking up any oxygen the cyanobacteria managed to produce 104 00:05:16.800 --> 00:05:18.639 that kept levels incredibly low. 105 00:05:18.759 --> 00:05:20.720 Okay, that makes sense. What was the other main idea? 106 00:05:20.920 --> 00:05:23.839 The other focused more on chemical sinks. Within the oceans 107 00:05:23.879 --> 00:05:27.639 themselves and maybe other microbes. The oceans were full of 108 00:05:27.720 --> 00:05:32.120 dissolved iron, for example, which rusts oxidizes very readily, So. 109 00:05:32.120 --> 00:05:34.920 The oceans themselves were acting like a giant rust bucket, 110 00:05:35.040 --> 00:05:36.800 consuming oxygen effectively. 111 00:05:36.879 --> 00:05:41.680 Yeah. Plus maybe other early microbes, non oxygen producing ones, 112 00:05:41.920 --> 00:05:44.920 were super efficient at gobbling up any organic matter or 113 00:05:44.959 --> 00:05:48.560 trace oxygen that appeared a biological sink working alongside the 114 00:05:48.639 --> 00:05:49.240 chemical ones. 115 00:05:49.279 --> 00:05:53.079 So you had this planetary tug of war cyanobacteria producing 116 00:05:53.120 --> 00:05:54.560 oxygen on one size. 117 00:05:54.240 --> 00:05:57.720 And volcanoes, ocean chemistry and maybe other microbes consuming it 118 00:05:57.759 --> 00:05:58.639 on the other side. 119 00:05:58.720 --> 00:06:01.319 And the argument was that these forces were just perfectly 120 00:06:01.360 --> 00:06:04.680 balanced for half a billion years. That seems improbable. 121 00:06:04.959 --> 00:06:08.120 That's the tricky part, isn't it. Maintaining such a perfect, 122 00:06:08.160 --> 00:06:11.480 delicate balance for such an incredibly long time and then 123 00:06:11.560 --> 00:06:15.279 having it suddenly fail. Yeah, it always felt a bit well, 124 00:06:15.639 --> 00:06:19.920 unsatisfying plausible. Sure, those factors were important, but maybe not 125 00:06:19.959 --> 00:06:20.519 the whole story. 126 00:06:20.560 --> 00:06:23.639 It didn't explain why the producers the cyanobacteria didn't just 127 00:06:23.680 --> 00:06:26.519 eventually overwhelm the sinks earlier exactly. 128 00:06:26.759 --> 00:06:30.279 The older models focused heavily on oxygen consumption. They didn't 129 00:06:30.319 --> 00:06:32.600 look as closely at factors that might have been limiting 130 00:06:32.600 --> 00:06:37.319 oxygen production in the first place by suppressing the cyanobacteria themselves. 131 00:06:36.839 --> 00:06:39.639 Which is where the okay, i'ma study pivots. They're looking 132 00:06:39.720 --> 00:06:43.839 at these cyanobacteria's diet, essentially their immediate chemical environment. 133 00:06:44.199 --> 00:06:48.399 That's the core idea. Looking for ecological constraints. Doctor Ratnac's 134 00:06:48.399 --> 00:06:52.360 team focused on trace elements and simple organic compounds, things 135 00:06:52.399 --> 00:06:54.680 that might be present in small amounts but could have 136 00:06:54.800 --> 00:06:56.839 huge regulatory effects on life. 137 00:06:57.079 --> 00:07:00.560 And they zeroed in on nickel and urea. Why those 138 00:07:00.600 --> 00:07:01.319 two They. 139 00:07:01.160 --> 00:07:04.519 Had a hunch based on biochemistry that these two might 140 00:07:04.560 --> 00:07:09.000 have this interconnected, really crucial role in limiting cyanobacterial growth. 141 00:07:09.279 --> 00:07:12.800 Specifically back in the rke and eon. They suspected an 142 00:07:12.839 --> 00:07:16.519 ecological control mechanism was the real bottleneck, something that didn't 143 00:07:16.519 --> 00:07:18.920 need a new evolution to overcome, just to change in 144 00:07:18.920 --> 00:07:20.519 the environment to release the brakes. 145 00:07:20.839 --> 00:07:25.519 Finding that microscopic switch in a giant planetary system, I'm hucked. 146 00:07:27.560 --> 00:07:30.480 All right, let's dive into the evidence itself Section two. 147 00:07:31.040 --> 00:07:34.360 How they actually tested this. This wasn't just computer modeling, right, 148 00:07:34.480 --> 00:07:35.600 They did lab experiment. 149 00:07:35.680 --> 00:07:38.240 Oh yeah, really, rigorous experimental work. It had to be 150 00:07:38.279 --> 00:07:41.360 done in two parts. Really. First, they needed to establish 151 00:07:41.360 --> 00:07:45.000 that their key players, Nickel and Urea, were actually plausible 152 00:07:45.040 --> 00:07:48.920 components of the early Archean ocean around say four to 153 00:07:48.959 --> 00:07:52.199 two point five billion years ago before the goe kicked off. 154 00:07:52.319 --> 00:07:54.160 Makes sense. You can't have them be the bottleneck if 155 00:07:54.160 --> 00:07:54.920 they weren't even. 156 00:07:54.720 --> 00:07:58.480 There precisely, So, Experiment Part one was all about abiotic 157 00:07:58.639 --> 00:08:02.040 Urea formation. The question us could urea, which we know 158 00:08:02.120 --> 00:08:05.680 is a vital nitrogen source for life, actually form without life, 159 00:08:05.680 --> 00:08:08.120 making it through purely chemical. 160 00:08:07.720 --> 00:08:10.959 Processes abiotic meaning non biological origin exactly. 161 00:08:11.000 --> 00:08:13.319 And they needed to simulate the conditions of early Earth, 162 00:08:13.519 --> 00:08:16.199 which were pretty brutal. Huw So well, the big thing 163 00:08:16.279 --> 00:08:19.160 is the lack of an ozone layer. Back then, Earth's 164 00:08:19.199 --> 00:08:22.399 early atmosphere didn't have much oxygen, so no ozone shield 165 00:08:22.480 --> 00:08:27.480 like we have today. That meant intense high energy ultraviolet radiation, 166 00:08:27.879 --> 00:08:32.679 specifically UVC was just blasting the surface, including the oceans. 167 00:08:32.360 --> 00:08:34.000 And uvc's pretty nasty stuff. 168 00:08:34.080 --> 00:08:34.200 Right. 169 00:08:34.240 --> 00:08:35.879 We use it for sterilization, we do. 170 00:08:35.960 --> 00:08:39.679 It's a highly energetic breaks down molecules, but that energy 171 00:08:39.720 --> 00:08:43.200 can also drive chemical reactions that wouldn't normally happen, so 172 00:08:43.320 --> 00:08:47.559 simulating that UVC exposure was crucial for accurately mimicking the 173 00:08:47.600 --> 00:08:51.120 prebiotic environment. If a reaction needed UVC, it might have 174 00:08:51.159 --> 00:08:52.159 happened then, but not now. 175 00:08:52.320 --> 00:08:55.440 Okay, so intense UV light. What ingredients did they put 176 00:08:55.519 --> 00:08:57.320 in their simulated primordial soup. 177 00:08:57.480 --> 00:08:59.320 They used a mix of simple stuff thought to be 178 00:08:59.399 --> 00:09:03.360 common back then, things like ammonium, cyanide and dissol iron compounds, 179 00:09:03.639 --> 00:09:08.200 basic building blocks readily available from volcanic outgassing or hydrothermal vents. 180 00:09:08.240 --> 00:09:11.159 And they zapped this mixture with UVC light. 181 00:09:11.320 --> 00:09:14.480 Yep, they exposed these mixtures to UVC radiation and then 182 00:09:14.480 --> 00:09:17.639 analyze the results to see if urea CONH two had formed, 183 00:09:17.720 --> 00:09:20.440 and did it it did. They confirmed that urea could 184 00:09:20.480 --> 00:09:24.200 indeed form abiotically under these plausible early Earth conditions. 185 00:09:24.480 --> 00:09:29.120 Why is that single finding so important for their overall argument. 186 00:09:29.519 --> 00:09:33.039 It's foundational because if urea could only be made by 187 00:09:33.159 --> 00:09:37.919 complex biological processes, then its availability in the Archian Ocean 188 00:09:38.039 --> 00:09:40.799 might have been really limited or patchy. Maybe that was 189 00:09:40.840 --> 00:09:43.720 the bottleneck, just not enough nitrogen in a usable form. 190 00:09:43.919 --> 00:09:46.440 But if it forms abiotically. 191 00:09:45.919 --> 00:09:49.159 Then it was likely just there a constant background component 192 00:09:49.200 --> 00:09:52.679 in the ancient oceans, produced by sunlight hitting common chemicals. 193 00:09:53.200 --> 00:09:55.320 It wasn't a rare nutrient that life had to invent 194 00:09:55.360 --> 00:09:58.120 ways to make. It was an environmental factor life had 195 00:09:58.120 --> 00:09:59.559 to deal with, for better or worse. 196 00:10:00.200 --> 00:10:02.799 So urea was likely present. Step one confirmed. What was 197 00:10:02.799 --> 00:10:04.320 step two? Experiment Part two? 198 00:10:04.519 --> 00:10:06.840 Right now? They needed to see how varying levels of 199 00:10:06.879 --> 00:10:10.039 this urea along with nickel actually affected the growth of 200 00:10:10.080 --> 00:10:14.720 the oxygen producers themselves. So testing cyanobacterial growth. 201 00:10:14.399 --> 00:10:17.159 And they needed a stand in for ancient cyanobacteria. 202 00:10:17.399 --> 00:10:21.399 Yeah, they used a well studied robust species called Cinachucoccus 203 00:10:21.559 --> 00:10:25.840 SPPCC seven thousand and two. It's a modern cyanobacterium, but 204 00:10:25.879 --> 00:10:28.440 it's often used as a model organism because it grows 205 00:10:28.480 --> 00:10:32.159 relatively quickly and its basic photosynthetic machinery is thought to 206 00:10:32.200 --> 00:10:34.159 be representative of those early forms. 207 00:10:34.399 --> 00:10:36.919 Makes sense, So how do they set up the growth tests? 208 00:10:37.000 --> 00:10:38.000 What were they controlling? 209 00:10:38.799 --> 00:10:41.679 It was all about careful control. They grew the senachure 210 00:10:41.720 --> 00:10:45.159 caucus under standard conditions, things like controlled like dark cycles 211 00:10:45.159 --> 00:10:48.120 to mimic day and night. But the key manipulation was 212 00:10:48.159 --> 00:10:51.399 the growth medium, the soup the sanobacteria lived in. 213 00:10:51.399 --> 00:10:53.240 They tweaked the recipe exactly. 214 00:10:53.480 --> 00:10:57.279 They created different patches with systematically varied concentrations of urea 215 00:10:57.399 --> 00:11:00.399 and nickel. Some batches had low urea, some high, some 216 00:11:00.519 --> 00:11:03.519 at low nickel, some high. And importantly, they tested various 217 00:11:03.519 --> 00:11:06.759 combinations high er low nickel, low uryhine, nickel high, high, 218 00:11:06.840 --> 00:11:11.279 lo low, all the possibilities, reflecting potential archeane conditions. 219 00:11:10.879 --> 00:11:12.879 Covering all the bases. And how did they track if 220 00:11:12.919 --> 00:11:15.159 the microups were actually growing well or not? How do 221 00:11:15.200 --> 00:11:15.720 you measure that? 222 00:11:16.039 --> 00:11:20.600 They use standard microbiology techniques. Two key metrics. First, they 223 00:11:20.600 --> 00:11:24.039 measure the optical density of the liquid culture, basically how 224 00:11:24.080 --> 00:11:28.600 cloudy it gets. As the cyanobacteria cells multiply, the culture 225 00:11:28.600 --> 00:11:32.320 becomes more turbid, blocking more light passing through it. More 226 00:11:32.360 --> 00:11:34.440 cloudiness equals more biomass. 227 00:11:34.000 --> 00:11:35.919 Okay, a measure of overall growth yep. 228 00:11:36.159 --> 00:11:38.879 And Second, they measure the concentration of chlorophyll. That's the 229 00:11:38.960 --> 00:11:44.399 main pigment cyanobacteria use for photosynthesis, So tracking chlorophyll gives 230 00:11:44.399 --> 00:11:47.879 you a direct measure of the photosynthetic capacity of the culture. 231 00:11:48.120 --> 00:11:50.120 How much oxygen making machinery is present. 232 00:11:50.480 --> 00:11:50.919 Got it? 233 00:11:51.440 --> 00:11:51.639 Two? 234 00:11:51.639 --> 00:11:53.840 Different ways to measure success. And what did they find? 235 00:11:54.000 --> 00:11:56.000 Was it just more urea, more growth? 236 00:11:56.200 --> 00:11:58.279 Not at all. It was much more complex. It wasn't 237 00:11:58.279 --> 00:12:01.679 a simple case of urea being just food. They found 238 00:12:01.759 --> 00:12:05.360 this intricate relationship, this dual role where the combination of 239 00:12:05.480 --> 00:12:08.159 nickel and urea concentrations was the critical factor. 240 00:12:08.360 --> 00:12:11.120 Doctor Rutnaya called it complex yet fascinating. 241 00:12:11.320 --> 00:12:14.440 Right, that's the quote. The key finding wasn't about the 242 00:12:14.480 --> 00:12:18.639 absolute amount of urea, but the ratio of nickel to urea. 243 00:12:19.360 --> 00:12:22.559 That ratio scene to dictate whether the cyanobacteria could actually 244 00:12:22.639 --> 00:12:26.200 flourish or if their growth was actively suppressed, even if 245 00:12:26.240 --> 00:12:29.120 there was plenty of nitrogen theoretically available in the form 246 00:12:29.120 --> 00:12:29.639 of urea. 247 00:12:29.799 --> 00:12:34.360 So it wasn't simple starvation. It was something more like interference. 248 00:12:33.759 --> 00:12:38.159 Exactly, pointing towards more subtle chemical control mechanism rather than 249 00:12:38.279 --> 00:12:40.039 just basic nutrient limitation. 250 00:12:40.200 --> 00:12:42.440 Okay, this is where it gets really interesting. Section three. 251 00:12:42.679 --> 00:12:47.879 Unpacking the biogeochemical bottleneck model itself. How did high nickel 252 00:12:47.879 --> 00:12:51.279 and urea actually work together to suppress life and delay 253 00:12:51.399 --> 00:12:52.039 the GOE? 254 00:12:52.399 --> 00:12:55.360 Right, this is the core of their proposed mechanism. To 255 00:12:55.440 --> 00:12:57.480 understand the bottleneck, you need to picture the rkey in 256 00:12:57.559 --> 00:13:01.679 ocean chemistry. The model suggests that back then concentrations of 257 00:13:01.720 --> 00:13:04.960 both nickel and urea were significantly higher than they are today, 258 00:13:05.200 --> 00:13:08.039 and crucially, it was this combination of high levels that 259 00:13:08.120 --> 00:13:09.240 acted as the suppressor. 260 00:13:09.399 --> 00:13:12.159 Okay, hang on, I'm still slightly stuck on why hy 261 00:13:12.320 --> 00:13:15.200 urea would be bad. We established it's a nitrogen source, 262 00:13:15.200 --> 00:13:18.799 and nitrogen is essential, right for proteins, DNA, everything, it 263 00:13:18.879 --> 00:13:22.519 is essential absolutely, and nickel isn't that also a trace 264 00:13:22.600 --> 00:13:26.600 nutrient needed for some enzymes? So why would having more 265 00:13:26.600 --> 00:13:30.399 of these essential things be bad? It feels counterintuitive, it does. 266 00:13:30.200 --> 00:13:33.759 Seem paradoxical, but the devil's in the biochemical details. It 267 00:13:33.799 --> 00:13:35.840 goes down to a specific enzyme called. 268 00:13:35.759 --> 00:13:37.720 Urese eurese Okay, what does that do? 269 00:13:38.279 --> 00:13:42.480 Cyanobacteria, like many organisms, can't use urea directly as is. 270 00:13:42.840 --> 00:13:45.399 They need to break it down first into simpler, more 271 00:13:45.440 --> 00:13:49.039 biologically available forms of nitrogen like ammonia. Use is the 272 00:13:49.120 --> 00:13:52.120 enzyme that does this job. It catalyzes the breakdown of urea. 273 00:13:52.159 --> 00:13:54.639 Okay, so use is the tool they use to process 274 00:13:54.679 --> 00:13:56.440 the urea food exactly. 275 00:13:56.960 --> 00:14:01.559 And here's the crucial link to nickel therese enzyme absolutely 276 00:14:01.600 --> 00:14:04.440 requires a tiny amount of nickel to function. Nickel acts 277 00:14:04.480 --> 00:14:07.360 as a cofactor, fitting into the enzyme's active site and 278 00:14:07.399 --> 00:14:08.799 helping it do its chemical work. 279 00:14:08.960 --> 00:14:10.000 So they do need nickel. 280 00:14:10.159 --> 00:14:13.200 They do, but only in trace amounts. Here's the problem. 281 00:14:13.600 --> 00:14:17.120 The Archean oceans were apparently swimming in nickel compared to today. 282 00:14:17.200 --> 00:14:18.759 Why so much nickel back then? 283 00:14:19.120 --> 00:14:21.919 It's linked to the Earth's geology. At the time, there 284 00:14:22.000 --> 00:14:25.799 was much higher geothermal activity, lots of deep sea hydroluminal 285 00:14:25.840 --> 00:14:30.399 events spewing out dissolved metals, and also a specific type 286 00:14:30.440 --> 00:14:34.320 of magnesium rich volcanic rock called comati eate was much 287 00:14:34.360 --> 00:14:37.039 more common than These rocks are very rich in nickel, 288 00:14:37.240 --> 00:14:40.360 and as they weathered or interacted with sea water, they 289 00:14:40.480 --> 00:14:41.679 released a lot of nickel. 290 00:14:41.799 --> 00:14:44.360 So nickel concentrations were way higher. 291 00:14:44.120 --> 00:14:47.240 Potentially orders of magnitude higher, maybe four hundred times the 292 00:14:47.240 --> 00:14:50.279 concentration we see in modern oceans based on geological evidence, 293 00:14:50.799 --> 00:14:52.840 way way above trace nutrient levels. 294 00:14:52.879 --> 00:14:55.679 Okay, so too much of a good thing. What happens 295 00:14:55.720 --> 00:14:59.440 when the ures enzyme encounters these super high nickel levels 296 00:14:59.480 --> 00:15:00.759 along with high urea. 297 00:15:01.240 --> 00:15:04.159 That's where the inhibition comes in. When nickel concentrations get 298 00:15:04.159 --> 00:15:06.399 that high, it stops being just a helpful cofactor and 299 00:15:06.440 --> 00:15:09.919 starts coming up the works. The excess nickel ions essentially 300 00:15:09.919 --> 00:15:12.679 compete for or interfere with the active site of the 301 00:15:12.759 --> 00:15:16.600 ures enzyme. They block it. They interfere, Yeah, especially when 302 00:15:16.600 --> 00:15:19.039 the enzyme is already trying to bind and process lots 303 00:15:19.039 --> 00:15:22.320 of UREA molecules. Because the UREA concentration is also high. 304 00:15:22.519 --> 00:15:25.919 It's like the enzyme gets overwhelmed and effectively poisoned or 305 00:15:26.039 --> 00:15:29.159 jammed by the sheer abundance of nickel ions hitting it 306 00:15:29.399 --> 00:15:30.919 while it's trying to work on the urea. 307 00:15:31.200 --> 00:15:34.240 Wow. So the cyanobacteria are floating in this ocean full 308 00:15:34.320 --> 00:15:38.000 of potential nitrogen fuel urea, but the tool they need 309 00:15:38.039 --> 00:15:41.600 to use that fuel, ureas, is constantly being sabotaged by 310 00:15:41.639 --> 00:15:43.039 the massive overdose of nickel. 311 00:15:43.240 --> 00:15:47.200 That's the bottleneck mechanism. In a nutshell, They're effectively starving 312 00:15:47.240 --> 00:15:49.440 for usable nitrogen right in the middle of the urea 313 00:15:49.480 --> 00:15:53.360 feast because their metabolic machinery to access it is chemically 314 00:15:53.360 --> 00:15:55.120 inhibited by the nickel overload. 315 00:15:55.200 --> 00:15:58.320 So they can't grow efficiently, they can't divide rapidly and 316 00:15:58.440 --> 00:15:59.559 form massive blooms. 317 00:15:59.639 --> 00:16:04.159 Exactly. Their proliferation is suppressed, you might get small, localized, 318 00:16:04.240 --> 00:16:08.440 short lived blooms perhaps, but not the sustained planet wide 319 00:16:08.440 --> 00:16:12.200 explosion of cyanobacteria needed to overwhelm the oxygen sinks and 320 00:16:12.240 --> 00:16:16.000 fundamentally change the atmosphere. The nickel urea combination acted like 321 00:16:16.039 --> 00:16:17.559 a powerful break on the whole system. 322 00:16:17.720 --> 00:16:21.000 That explains the lights off period, the great delay. The 323 00:16:21.039 --> 00:16:24.759 factory was built, the fuel urea was there, but a 324 00:16:24.840 --> 00:16:27.840 key piece of machinery UYS was jammed by nickel. 325 00:16:28.039 --> 00:16:31.159 Okay, so what released the break? What caused the tipping 326 00:16:31.200 --> 00:16:32.360 point for the goe? 327 00:16:32.679 --> 00:16:35.679 According to this model, the trigger wasn't some new biological 328 00:16:35.759 --> 00:16:39.200 invention or mutation in the cyanobacteria. It was a gradual, 329 00:16:39.440 --> 00:16:43.440 large scale change in Earth's geochemistry that naturally lowered the 330 00:16:43.519 --> 00:16:45.200 nickel concentration in the oceans. 331 00:16:45.480 --> 00:16:48.840 The planet itself changed the conditions. How why would nickel 332 00:16:48.879 --> 00:16:49.559 levels drop? 333 00:16:49.720 --> 00:16:53.279 This links back to major geological shifts happening around that time, 334 00:16:53.480 --> 00:16:56.519 roughly two point five billion years ago, the Earth's mantle 335 00:16:56.720 --> 00:17:00.240 was slowly cooling down less internal heat, less internal heat, 336 00:17:00.279 --> 00:17:04.079 which meant overall volcanic activity likely decreased. Somewhat Crucially, the 337 00:17:04.119 --> 00:17:07.599 formation of those super nickel rich comatite rocks largely ceased. 338 00:17:07.920 --> 00:17:10.559 The source of excessive nickel started to dwindle. 339 00:17:10.240 --> 00:17:13.160 Okay less input from volcanoes and at the same time 340 00:17:13.759 --> 00:17:18.240 large stable continental land mass as Cretans were forming and growing. 341 00:17:18.839 --> 00:17:22.759 The emergence of continents changed global weathering patterns. More land 342 00:17:22.799 --> 00:17:26.759 surface means different types of chemical weathering, potentially locking up 343 00:17:26.839 --> 00:17:29.680 nickel and minerals on land rather than letting it wash 344 00:17:29.720 --> 00:17:30.279 into the sea. 345 00:17:30.680 --> 00:17:34.799 So less nickel coming in from volcanic sources and maybe 346 00:17:34.839 --> 00:17:39.119 more getting trapped on land or in sediments. The overall supply. 347 00:17:39.000 --> 00:17:42.680 Dropped exactly the input decreased, the sinks might have changed, 348 00:17:43.039 --> 00:17:46.519 and gradually, over millions of years, the concentration of dissolved 349 00:17:46.559 --> 00:17:50.079 nickel in the oceans fell. It dropped from those incredibly 350 00:17:50.160 --> 00:17:54.200 high inhibitory archaean levels down to something much closer to 351 00:17:54.240 --> 00:17:56.039 the trace nutrient levels we see today. 352 00:17:56.119 --> 00:17:59.240 It crossed a threshold below the level where it poisoned 353 00:17:59.240 --> 00:18:00.680 the urresenz that's. 354 00:18:00.519 --> 00:18:04.160 The critical idea. Once nickel dropped below that toxic threshold, 355 00:18:04.359 --> 00:18:07.240 the urease enzyme was finally free to work efficiently again. 356 00:18:07.680 --> 00:18:11.720 Cyanobacteria could now effectively utilize the urea that was still present. 357 00:18:11.599 --> 00:18:13.160 The metabolic break was released. 358 00:18:13.440 --> 00:18:18.680 The break was off with non inhibitory nickel levels, candobacteria 359 00:18:18.720 --> 00:18:21.680 could access the nitrogen they needed, and they began to 360 00:18:21.720 --> 00:18:26.759 proliferate massively globally, sustained large scale growth. 361 00:18:26.480 --> 00:18:30.359 And that sustained massive growth finally produced oxygen faster than 362 00:18:30.400 --> 00:18:32.519 the geological and chemical sinks could keep up. 363 00:18:32.720 --> 00:18:36.279 That is the Great oxidation event, triggered by the geologically 364 00:18:36.359 --> 00:18:38.160 driven decline in oceanic nickel. 365 00:18:38.359 --> 00:18:42.640 Wow. That really reframes the whole story. It wasn't about 366 00:18:43.119 --> 00:18:46.160 waiting for life to figure out oxygen production. It was 367 00:18:46.200 --> 00:18:49.640 about waiting for the planet's chemistry to allow the oxygen 368 00:18:49.640 --> 00:18:51.119 producers to truly take over. 369 00:18:51.359 --> 00:18:54.680 It puts the timing squarely in the core of planetary geochemistry, 370 00:18:54.720 --> 00:18:58.720 controlling microbioly ecology. The moderation of nickel, and by extension, 371 00:18:58.759 --> 00:19:01.519 the effective usability of us Rhea pave the way for 372 00:19:01.559 --> 00:19:02.559 the oxygenated world. 373 00:19:02.640 --> 00:19:06.000 A much clearer, more mechanistic explanation for that huge delay. 374 00:19:06.359 --> 00:19:08.480 This is fascinating just for understanding Earth history. But you 375 00:19:08.519 --> 00:19:11.400 mentioned earlier this has implications beyond our own planet. Let's 376 00:19:11.440 --> 00:19:14.440 get into that in section four. So what for searching 377 00:19:14.440 --> 00:19:15.400 for life elsewhere. 378 00:19:15.720 --> 00:19:19.359 Absolutely, this is where the research really connects to astrobiology. 379 00:19:19.559 --> 00:19:22.599 Doctor Ratniak explicitly points this out. If we want to 380 00:19:22.640 --> 00:19:27.319 find life on other planets, understanding the mechanisms that allowed 381 00:19:27.400 --> 00:19:31.599 life here to fundamentally reshape its environment is critical. 382 00:19:31.680 --> 00:19:33.920 It's not just about finding life, but finding life that's 383 00:19:33.960 --> 00:19:35.880 had a planetary impact. 384 00:19:35.559 --> 00:19:38.559 Or understanding why it hasn't even if it exists. We 385 00:19:38.599 --> 00:19:42.599 often assume that if life evolves, it will inevitably boom 386 00:19:42.680 --> 00:19:46.400 and change its planet, maybe producing biosignatures like oxygen that 387 00:19:46.440 --> 00:19:49.559 we can detect. But this study is a powerful reminder 388 00:19:49.599 --> 00:19:53.319 that life can exist for vast periods while being ecologically 389 00:19:53.359 --> 00:19:54.640 suppressed stuck. 390 00:19:54.839 --> 00:19:58.400 So when doctor Ratnek says this sheds light on biosignature detection, 391 00:19:58.680 --> 00:20:00.440 it's not just about looking for oxygen. 392 00:20:00.480 --> 00:20:03.720 It's about looking for oxygen in context or perhaps explaining 393 00:20:03.759 --> 00:20:06.759 its absence. Imagine we find an exoplanet that looks potentially 394 00:20:06.759 --> 00:20:09.559 habitable with the right temperature, maybe signs of water. We 395 00:20:09.640 --> 00:20:12.519 analyze its atmosphere, maybe we don't see much oxygen. 396 00:20:12.559 --> 00:20:15.319 We might assume life isn't there or isn't photosynthetic. 397 00:20:15.559 --> 00:20:19.240 Right, But this research gives us another possibility. Maybe life 398 00:20:19.319 --> 00:20:23.119 is there, Maybe it even invented oxygenic photosynthesis, but it's 399 00:20:23.119 --> 00:20:26.160 stuck in its own great oxidation delay because of a 400 00:20:26.240 --> 00:20:30.359 chemical bottleneck. Maybe its star system or planetary geology keeps 401 00:20:30.440 --> 00:20:33.400