1 00:00:04,280 --> 00:00:07,360 This is Geology Bites with Oliver Strimpel. 2 00:00:08,760 --> 00:00:14,240 Today, coral reefs host a wide range of ecological niches that 3 00:00:14,240 --> 00:00:18,160 support the most biologically diverse ecosystems on Earth. 4 00:00:19,520 --> 00:00:22,920 Did the emergence of such reefs in the Cambrian lay the 5 00:00:22,920 --> 00:00:25,520 groundwork for the Cambrian explosion of life? 6 00:00:26,800 --> 00:00:31,480 The answer may be yes, but it was not modern corals, which did 7 00:00:31,480 --> 00:00:35,160 not arrive on the scene until the Mid Triassic, over 250 8 00:00:35,160 --> 00:00:39,600 million years later. So what were the first reef 9 00:00:39,600 --> 00:00:43,560 builders? Sarah Proust studies early 10 00:00:43,560 --> 00:00:46,880 animal evolution and the carbonate records they leave. 11 00:00:47,600 --> 00:00:50,920 She's especially interested in reef systems and how they 12 00:00:50,920 --> 00:00:54,520 persist and recur through geological time, despite the 13 00:00:54,520 --> 00:00:56,560 environmental stresses imposed on them. 14 00:00:57,320 --> 00:01:00,200 She's a professor of geosciences at Smith College. 15 00:01:01,200 --> 00:01:03,800 Sarah Preuss, welcome to Geology Bites. 16 00:01:04,120 --> 00:01:05,600 Oliver, thank you so much for having me. 17 00:01:05,880 --> 00:01:09,720 I said that the first reefs that emerged in the Cambrian were not 18 00:01:09,720 --> 00:01:14,080 the work of modern day corals, So what was it that built them? 19 00:01:14,640 --> 00:01:18,840 So the first animal reefs that show up on the scene are built 20 00:01:18,840 --> 00:01:22,760 by an ancient group of sponges called archaeosciaths. 21 00:01:23,360 --> 00:01:28,840 And archaeocyaths were some of these first calcareous sponges 22 00:01:28,840 --> 00:01:32,840 that in many ways look like corals and resemble them. 23 00:01:32,840 --> 00:01:36,400 They have branching morphologies and built structures on the sea 24 00:01:36,400 --> 00:01:41,200 floor, but were very much sponges that worked in a 25 00:01:41,200 --> 00:01:45,560 relationship or in a consortium with microbial organisms as well 26 00:01:45,800 --> 00:01:49,440 to construct these reefs. So in some cases, the reefs 27 00:01:49,440 --> 00:01:53,680 themselves can be predominantly made by microbial organisms with 28 00:01:53,680 --> 00:01:56,040 archaeocias sort of tagging along. 29 00:01:56,320 --> 00:01:59,560 And then in some cases, the archaeocias themselves really do 30 00:01:59,560 --> 00:02:02,560 build the frame of the reef, almost like the backbone of a 31 00:02:02,560 --> 00:02:04,640 reef. And there was a long debate 32 00:02:04,840 --> 00:02:09,120 about what they were and who they were and whether they were 33 00:02:09,120 --> 00:02:12,240 a coral or some other kind of Organism. 34 00:02:12,240 --> 00:02:15,080 But I think there's broad consensus now that they are most 35 00:02:15,080 --> 00:02:16,600 closely aligned with the sponges. 36 00:02:17,160 --> 00:02:20,840 And how far back in the tree of life do sponges go? 37 00:02:21,240 --> 00:02:25,240 Sponges go quite a ways back, although their fossil record 38 00:02:25,240 --> 00:02:28,720 does not extend as far back as we think they may have been 39 00:02:28,720 --> 00:02:31,120 around. We're always trying to fill in 40 00:02:31,120 --> 00:02:33,720 that gap. There are chemical records 41 00:02:33,720 --> 00:02:37,920 called biomarkers that suggest that sponges go quite deep into 42 00:02:37,920 --> 00:02:41,920 time, hundreds of millions of years really before they show up 43 00:02:42,280 --> 00:02:44,160 in the Cambrian as the Archaeosiaths. 44 00:02:44,240 --> 00:02:49,640 And there are putative sponges, fossils that go back quite into 45 00:02:49,640 --> 00:02:52,680 deep time, but they tend to be debated. 46 00:02:52,760 --> 00:02:56,440 There aren't, I don't think, ones that sort of have universal 47 00:02:56,440 --> 00:03:00,760 agreement at this point, but there is some emerging agreement 48 00:03:00,760 --> 00:03:03,840 around the biomarker record and that there are these chemical 49 00:03:03,840 --> 00:03:06,640 traces of sponges that go quite deep in time. 50 00:03:07,040 --> 00:03:11,160 But we actually have some fossils from the late 51 00:03:11,160 --> 00:03:15,160 Proteozoic, from the Ediacran period, sort of soft bodied 52 00:03:15,160 --> 00:03:17,240 creatures. In a previous episode of Geology 53 00:03:17,240 --> 00:03:19,800 Bites, Rachel Wood spoke a little bit about those. 54 00:03:20,360 --> 00:03:22,560 These are not related to those, are they? 55 00:03:22,840 --> 00:03:25,880 These archaeocyaths are probably different. 56 00:03:25,880 --> 00:03:29,680 They are biomineralizing organisms, and sponges in 57 00:03:29,680 --> 00:03:33,800 general are a sort of messy group where there are some 58 00:03:33,840 --> 00:03:37,760 questions about their relationships to each other. 59 00:03:38,280 --> 00:03:42,720 What enabled the archaeocytes to emerge during the Cambrian? 60 00:03:42,720 --> 00:03:45,440 And when they did emerge, were they very widespread? 61 00:03:45,800 --> 00:03:50,360 One of the interesting things that seems to be happening 62 00:03:50,360 --> 00:03:53,480 broadly across different groups is this onset of 63 00:03:53,480 --> 00:03:56,600 biomineralization as part of the Cambrian explosion. 64 00:03:57,040 --> 00:04:00,920 We see the roots of that in the Ediacran, but really there is an 65 00:04:00,920 --> 00:04:03,680 expansion that happens in Cambrian time. 66 00:04:04,160 --> 00:04:09,160 And so archaeocyas were clearly a group of sponges that 67 00:04:09,160 --> 00:04:12,560 developed the ability to make a skeleton to biomineralize. 68 00:04:12,840 --> 00:04:17,000 And when they show up in the fossil record, they are quite 69 00:04:17,000 --> 00:04:19,880 widespread. They are a very common component 70 00:04:19,880 --> 00:04:22,800 of what we would consider the Cambrian fauna. 71 00:04:22,880 --> 00:04:26,240 They appear in the early Cambrian and on a variety of 72 00:04:26,560 --> 00:04:30,960 paleocontinents. So they were globally quite 73 00:04:31,000 --> 00:04:34,400 significant, but geologically very short lived. 74 00:04:34,800 --> 00:04:38,920 Did they create ecological niches that facilitated the 75 00:04:38,920 --> 00:04:42,800 growth and diversity? Well, I would argue based on 76 00:04:42,840 --> 00:04:45,240 some work that I've done with students over the years, and I'm 77 00:04:45,240 --> 00:04:47,880 sure you could bring on others that might say something 78 00:04:47,880 --> 00:04:51,000 different, but I would argue that the structures that they 79 00:04:51,000 --> 00:04:55,400 built were quite important to facilitating local diversity. 80 00:04:55,840 --> 00:04:59,520 And so if we think about modern reef ecosystems, we see that in 81 00:04:59,520 --> 00:05:03,200 many modern reef ecosystems, diversity tends to be high and 82 00:05:03,200 --> 00:05:06,320 it tends to be places where there are a variety of 83 00:05:06,320 --> 00:05:08,480 environments that can be preserved because they're 84 00:05:08,480 --> 00:05:10,200 structures built on the sea floor. 85 00:05:10,720 --> 00:05:13,440 Animals can capitalize on those different, you know, sort of 86 00:05:13,440 --> 00:05:16,840 micro environments and thrive. And it's no different in the 87 00:05:16,840 --> 00:05:20,880 Archaeosiaths when we examine the Archaeosiath reefs in deep 88 00:05:20,880 --> 00:05:23,360 time and we look at the components of things that we're 89 00:05:23,360 --> 00:05:26,640 living within them, as well as the organisms that we're living 90 00:05:26,640 --> 00:05:29,560 on and around them. The diversity and abundance of 91 00:05:29,560 --> 00:05:33,680 animals tends to be locally higher in those reef ecosystems. 92 00:05:33,840 --> 00:05:37,160 So I think they had an important role to play as part of this 93 00:05:37,160 --> 00:05:40,880 kind of Cambrian explosion in reef environments and 94 00:05:40,880 --> 00:05:44,200 particularly for organisms that made shells for biomineralizing 95 00:05:44,200 --> 00:05:46,360 organisms. That's fascinating, actually. 96 00:05:46,360 --> 00:05:50,120 It reminds me of the episode I did with Paul Smith, who talked 97 00:05:50,120 --> 00:05:53,880 about the Cambrian explosion and the many processes that he 98 00:05:53,880 --> 00:05:58,080 suggested were responsible for the very rapid rise in animal 99 00:05:58,080 --> 00:05:59,800 diversity in the Middle Cambrian. 100 00:06:00,440 --> 00:06:05,480 So does our understanding of the archaeosias and their reefs and 101 00:06:05,480 --> 00:06:09,360 the biomineralization they were able to do give us insight into 102 00:06:09,360 --> 00:06:12,120 some of these processes and really help us understand how 103 00:06:12,120 --> 00:06:13,800 the Cambrian explosion came about? 104 00:06:14,520 --> 00:06:17,120 It's tricky. I think that the Cambrian 105 00:06:17,120 --> 00:06:22,280 explosion, the actual mechanisms of it are still debated. 106 00:06:22,520 --> 00:06:27,240 I do think that there's some combination of, you know, going 107 00:06:27,240 --> 00:06:30,960 back to Charles Marshall's 2006 paper, some component of 108 00:06:31,280 --> 00:06:35,800 environment, ecosystem and genetic toolkit that all played 109 00:06:35,800 --> 00:06:39,560 together to facilitate this moment where organisms were 110 00:06:39,560 --> 00:06:43,480 interacting and occupying new ecospace in ways that they 111 00:06:43,480 --> 00:06:46,320 hadn't before. I think another interesting 112 00:06:46,360 --> 00:06:48,560 piece of this is the disappearance of the 113 00:06:48,560 --> 00:06:51,680 Archaeosiath reefs. Because in a paper our group put 114 00:06:51,680 --> 00:06:56,120 out just this last year, we documented that when these 115 00:06:56,120 --> 00:07:00,840 Archaeosiath reefs go away to skeletal organisms as in terms 116 00:07:00,840 --> 00:07:04,640 of their abundance and to some extent their diversity remains 117 00:07:04,640 --> 00:07:08,040 low for a period of time. And that suggests that these 118 00:07:08,040 --> 00:07:12,760 reefs played an important ecological role in facilitating 119 00:07:12,760 --> 00:07:15,080 where these animals were living and how they they were living. 120 00:07:15,520 --> 00:07:19,800 And whatever stresses caused those reefs to disappear, 121 00:07:19,800 --> 00:07:23,480 whether it was low oxygen, whether it was extreme warming, 122 00:07:23,480 --> 00:07:26,880 various mechanisms that we could think about, whatever stresses 123 00:07:26,920 --> 00:07:31,840 those were, really did lead to this long term decline of animal 124 00:07:31,840 --> 00:07:34,680 diversity and abundance. So I think they provide both 125 00:07:34,680 --> 00:07:39,480 insights into the Cambrian explosion itself, but also the 126 00:07:39,480 --> 00:07:43,320 broader view of environments and ecosystems within the Cambrian 127 00:07:43,720 --> 00:07:46,680 and the stresses that organisms were experiencing during this 128 00:07:46,760 --> 00:07:48,920 critical moment in evolutionary history. 129 00:07:49,240 --> 00:07:52,400 So that's interesting. Naively, I had thought of the 130 00:07:52,400 --> 00:07:56,640 Cambrian explosion as initially a rapid, but then also an 131 00:07:56,640 --> 00:08:01,040 ongoing increase in animal diversity, at least until the 132 00:08:01,040 --> 00:08:05,680 end of the Cambrian. But in fact, after the initial 133 00:08:05,680 --> 00:08:09,800 burst of diversity in the Early Cambrian, sometime in the Middle 134 00:08:09,800 --> 00:08:13,080 Cambrian, it went into reverse and there was a decline. 135 00:08:13,640 --> 00:08:19,400 So when did the archaeosias actually disappear, and was it 136 00:08:19,600 --> 00:08:22,960 one of the various stresses that you enumerated that finally 137 00:08:22,960 --> 00:08:25,120 polished them off? Yeah, it's, it's a good 138 00:08:25,120 --> 00:08:27,440 question. I think one of the things that 139 00:08:27,440 --> 00:08:30,120 can be challenging about studying the Archaeosiath 140 00:08:30,120 --> 00:08:34,320 extinction is that we have somewhat poor age constraints on 141 00:08:34,320 --> 00:08:37,159 the Cambrian. So whether or not the reefs 142 00:08:37,200 --> 00:08:40,880 disappearing in Mongolia times exactly with the reefs 143 00:08:40,880 --> 00:08:44,560 disappearing in the Western US has remained A somewhat open 144 00:08:44,560 --> 00:08:47,440 question because of our difficulty in correlating 145 00:08:47,440 --> 00:08:50,280 between these global units. And it's something that's 146 00:08:50,280 --> 00:08:53,320 playing out in a variety of different Cambrian working 147 00:08:53,320 --> 00:08:56,040 groups and discussions that I'm involved in right now is just 148 00:08:56,040 --> 00:08:58,280 linking the sections together can be challenging. 149 00:08:58,680 --> 00:09:02,120 However, one wants to think about the ways in which these 150 00:09:02,120 --> 00:09:05,680 sections may represent a synchronous extinction or a 151 00:09:05,680 --> 00:09:09,000 period, an interval of extinction, during which these 152 00:09:09,000 --> 00:09:12,800 reefs disappear. They do go away globally and by 153 00:09:12,800 --> 00:09:16,480 Middle Cambrian time are really archosiath reefs are thought to 154 00:09:16,480 --> 00:09:21,640 be gone, a thing of the past. I think there's some evidence 155 00:09:21,640 --> 00:09:25,120 for oxygen stress that may have played a role in the 156 00:09:25,120 --> 00:09:27,200 disappearance of these organisms. 157 00:09:27,480 --> 00:09:32,080 I think sometimes with oxygen stress, there can also be stress 158 00:09:32,080 --> 00:09:33,920 in how organisms make their shells. 159 00:09:34,360 --> 00:09:38,240 So a related stress to organisms that's biologically relevant in 160 00:09:38,240 --> 00:09:42,040 addition to low oxygen in the environment broadly, is it can 161 00:09:42,040 --> 00:09:44,680 become difficult to make a shell. 162 00:09:44,680 --> 00:09:48,560 And so that may have been another stress that these 163 00:09:48,560 --> 00:09:52,960 organisms were grappling with. So does the relatively rapid 164 00:09:53,440 --> 00:09:57,480 rise and fall, geologically Speaking, of the archaeosias 165 00:09:57,600 --> 00:10:01,680 tell us that in fact ecosystems were less stable during the 166 00:10:01,680 --> 00:10:04,160 Cambrian because of all the stresses you talked about? 167 00:10:04,880 --> 00:10:08,720 I like to think of it as when I wrote a paper with my colleague 168 00:10:08,840 --> 00:10:12,480 a few years ago, Life on the Edge was the title of the paper. 169 00:10:12,560 --> 00:10:16,960 And it's this notion that these organisms and ecosystems are 170 00:10:18,040 --> 00:10:22,560 developing and existing in a world where stress is pervasive, 171 00:10:22,800 --> 00:10:27,880 where you have intervals of low oxygen adjacent to areas that 172 00:10:27,880 --> 00:10:31,440 are more rich in oxygen, and there's environmental 173 00:10:31,440 --> 00:10:33,880 heterogeneity. Rachel Wood, who you mentioned 174 00:10:33,880 --> 00:10:37,760 earlier, and Doug Irwin wrote a beautiful paper about how that 175 00:10:37,760 --> 00:10:41,520 environmental heterogeneity might actually be a driver of 176 00:10:41,800 --> 00:10:44,960 innovation for animals because they are having to adapt to such 177 00:10:44,960 --> 00:10:47,760 a wide array of stresses and environments. 178 00:10:48,080 --> 00:10:50,400 So I think it's a really interesting way to think about 179 00:10:50,400 --> 00:10:53,560 the Cambrian as a bunch of organisms and ecosystems that 180 00:10:53,560 --> 00:10:56,800 are living on the edge of environmental stress, and 181 00:10:56,800 --> 00:10:58,800 sometimes that stress gets to be too much. 182 00:10:59,280 --> 00:11:04,320 I meant to ask you about what evidence we actually have for 183 00:11:04,320 --> 00:11:08,040 the archaeoscience. You mentioned biomineralization 184 00:11:08,040 --> 00:11:11,760 and chemical evidence. Do we have any body fossils that 185 00:11:11,760 --> 00:11:15,480 enabled us to infer the morphology that you described? 186 00:11:15,800 --> 00:11:19,840 We have beautiful body fossils of archaeociats, and it's one of 187 00:11:19,840 --> 00:11:23,960 the great benefits of them having been biomineralizers is 188 00:11:23,960 --> 00:11:28,160 they leave behind a remnant calcium carbonate skeleton, and 189 00:11:28,280 --> 00:11:30,640 it can be preserved in a variety of ways. 190 00:11:30,640 --> 00:11:35,640 We once reported on archaeociats that were actually phosphatized, 191 00:11:35,640 --> 00:11:40,080 so appetite was a mineral that grew inside their pore spaces 192 00:11:40,240 --> 00:11:42,840 preserve them. They can be preserved as 193 00:11:43,040 --> 00:11:45,640 replaced calcium carbonate skeletons. 194 00:11:45,920 --> 00:11:48,920 They can be solicified, but the fact that they made a shell 195 00:11:49,120 --> 00:11:51,400 actually makes their record quite outstanding. 196 00:11:51,920 --> 00:11:54,960 And so there are ways in which we can examine their 197 00:11:54,960 --> 00:11:58,960 morphologies quite closely and really see how they lived, what 198 00:11:58,960 --> 00:12:01,920 their relationship was to the microbial organisms that shared 199 00:12:01,920 --> 00:12:05,160 their reefs, whether or not they were branching, whether or not 200 00:12:05,160 --> 00:12:08,880 they were more as existing solitarily as individuals. 201 00:12:09,280 --> 00:12:12,280 So you have the fossil record of archaeocyats is actually quite 202 00:12:12,560 --> 00:12:15,240 enjoyable to study. Where do we find some of the 203 00:12:15,240 --> 00:12:20,440 best preserved fossils? Oh, there are so many places 204 00:12:20,440 --> 00:12:22,840 that where Archaeosiath reefs have showed up over time. 205 00:12:22,840 --> 00:12:25,800 We have beautiful examples that I just walked over with my 206 00:12:25,800 --> 00:12:29,320 students in the western US, beautiful Archaeosiath reefs, 207 00:12:29,520 --> 00:12:32,760 particularly ones I'm familiar with in the Paleta Formation and 208 00:12:32,760 --> 00:12:35,280 Harkless Formation. They're like fun old friends to 209 00:12:35,280 --> 00:12:37,680 go back and visit. There are beautiful reefs that 210 00:12:37,680 --> 00:12:40,640 have been preserved in Australia and Mongolia. 211 00:12:40,640 --> 00:12:44,080 Mongolia has some really exceptional examples, South 212 00:12:44,080 --> 00:12:49,400 China, up in Arctic Canada, there's just a whole variety of 213 00:12:49,400 --> 00:12:52,560 places one can go, which again, just sort of points to 214 00:12:52,760 --> 00:12:56,960 ecologically how significant these must have been because of 215 00:12:56,960 --> 00:13:00,400 how widespread they were, even though they only existed for a 216 00:13:00,400 --> 00:13:03,080 relatively short period of time geologically speaking. 217 00:13:03,520 --> 00:13:07,600 You mentioned they had a certain kind of symbiosis with a 218 00:13:07,600 --> 00:13:11,080 microbial life. Is that analogous to the kind of 219 00:13:11,080 --> 00:13:15,680 symbiosis that modern corals have with the sort of polyps 220 00:13:15,680 --> 00:13:18,040 that live inside them? It's a great question. 221 00:13:18,040 --> 00:13:21,520 I think we don't entirely know, but there seems to be some 222 00:13:21,520 --> 00:13:25,960 evidence from, it's been argued that some archaeocyas that seem 223 00:13:25,960 --> 00:13:30,200 to have evidence of microbial textures inside the skeleton 224 00:13:30,440 --> 00:13:33,960 that it's possible that these were living symbiotically or at 225 00:13:33,960 --> 00:13:35,880 least they didn't mind each other. 226 00:13:35,880 --> 00:13:37,960 If they weren't directly benefiting each other, then 227 00:13:37,960 --> 00:13:40,640 perhaps they were living in a way that they didn't mind each 228 00:13:40,640 --> 00:13:44,200 other. So it's a bit different because 229 00:13:44,400 --> 00:13:47,320 the zozanthellae that live inside modern corals are 230 00:13:47,320 --> 00:13:52,120 photosynthetic organisms, and So what they provide for those 231 00:13:52,120 --> 00:13:55,840 corals is food that might be otherwise hard to get because 232 00:13:55,840 --> 00:13:58,960 the corals are sometimes living in low nutrient, low food 233 00:13:58,960 --> 00:14:02,680 environments and having those organisms that can provide food 234 00:14:02,680 --> 00:14:06,960 for them is very beneficial. It's a little bit more difficult 235 00:14:06,960 --> 00:14:10,520 to understand exactly what it would have been for sponges that 236 00:14:10,520 --> 00:14:13,640 would have been beneficial. Sponges are are these kind of 237 00:14:13,640 --> 00:14:16,760 heterotrophic organisms that seem to have lived in slightly 238 00:14:17,040 --> 00:14:19,640 potentially more nutrient rich settings. 239 00:14:19,640 --> 00:14:23,360 So did they need the microbes as a source of food or not? 240 00:14:23,440 --> 00:14:24,800 I think that's not entirely clear. 241 00:14:25,560 --> 00:14:30,640 After the archaeocytes went extinct, was there a gap in reef 242 00:14:30,640 --> 00:14:33,800 building or did other reef builders emerge pretty much 243 00:14:33,800 --> 00:14:36,600 right away? There is a gap, and certainly 244 00:14:36,600 --> 00:14:41,120 calcareous biomineralizing organisms experience a 245 00:14:41,120 --> 00:14:44,520 reasonably significant gap. It's not until the early or 246 00:14:44,520 --> 00:14:48,480 division that you start to see more enigmatic calcareous 247 00:14:48,480 --> 00:14:50,920 organisms showing up and moving into reefs. 248 00:14:51,400 --> 00:14:55,440 However, there have been a few examples, I believe from the 249 00:14:55,440 --> 00:14:59,240 Middle Cambrian, certainly from Upper Cambrian strata where 250 00:14:59,240 --> 00:15:04,480 there are microbial reefs that people have found sponges living 251 00:15:04,480 --> 00:15:06,720 in and perhaps adding some framework to. 252 00:15:07,200 --> 00:15:10,640 Many of those sponges are salacious and we're not probably 253 00:15:10,640 --> 00:15:13,960 originally calcareous as the archaeocyats were. 254 00:15:14,360 --> 00:15:18,480 And it's unclear that they were necessarily frame building 255 00:15:18,480 --> 00:15:21,480 sponges, but they were certainly living in the reefs. 256 00:15:21,720 --> 00:15:25,680 And so people have increasingly been quote UN quote filling in 257 00:15:25,680 --> 00:15:29,720 the reef gap by examining some of these microbial sponge reefs 258 00:15:29,720 --> 00:15:33,400 that would have existed after archaeoscience disappeared and 259 00:15:33,400 --> 00:15:37,360 before you start to see the more rise of sponge and coral reefs 260 00:15:37,360 --> 00:15:40,640 that dominate the Paleozoic. But the calcareous organisms 261 00:15:40,640 --> 00:15:43,480 that take over in the Early or Division, at least based on the 262 00:15:43,480 --> 00:15:46,600 reefs that I've spent time examining, are the ones that 263 00:15:46,600 --> 00:15:50,440 most remind me of the Archaeosiath structures of the 264 00:15:50,440 --> 00:15:54,360 Early Cambrian. And how long did those reef 265 00:15:54,360 --> 00:15:58,440 builders last, and were they then succeeded by the kind of 266 00:15:58,440 --> 00:16:02,320 corals that we have today? So those reef builders, the 267 00:16:02,320 --> 00:16:07,160 enigmatic ones, again, they show up for a bit, but they don't 268 00:16:07,160 --> 00:16:09,680 persist for a terribly long period of time. 269 00:16:10,000 --> 00:16:13,920 By the middle or division sort of later or division into the 270 00:16:13,920 --> 00:16:17,720 Silurian, you have stromatopyroid sponges and 271 00:16:17,720 --> 00:16:21,880 Paleozoic corals that start to show up and build reefs in the 272 00:16:21,880 --> 00:16:25,240 Paleozoic. But the real modern reefs, the 273 00:16:25,240 --> 00:16:29,000 scleractinian corals that build the modern reefs, do not show up 274 00:16:29,000 --> 00:16:34,440 until middle triathlon time, so more like 240 million years 275 00:16:34,440 --> 00:16:37,760 before present. So there are these intervals of 276 00:16:38,240 --> 00:16:42,440 reef building that are populated by different reef builders. 277 00:16:42,840 --> 00:16:46,840 And were those earlier reef builders rendered extinct by the 278 00:16:46,920 --> 00:16:50,160 N Permian extinction that was such a massive extinction? 279 00:16:50,520 --> 00:16:54,840 The stromatopyroid sponges that were a really big part of kind 280 00:16:54,840 --> 00:16:59,560 of Devonian reefs, they take a big hit in the late Devonian, 281 00:17:00,000 --> 00:17:03,560 the tabulate and the burgosid corals that are a part of the 282 00:17:03,560 --> 00:17:07,480 Paleozoic sort of reef building fauna, they persist that. 283 00:17:07,480 --> 00:17:11,160 Then the end Permian is really the thing that takes out the 284 00:17:11,160 --> 00:17:13,480 last of the Paleozoic reef builders. 285 00:17:13,720 --> 00:17:16,240 And so we get almost a complete reset. 286 00:17:16,240 --> 00:17:19,920 And in fact, if you go look at Lower Triassic sections around 287 00:17:19,920 --> 00:17:23,359 the world, what you see again is microbes. 288 00:17:23,560 --> 00:17:27,760 It's microbes that's take over as the interim reef builder when 289 00:17:27,760 --> 00:17:29,720 calcareous organisms are struggling. 290 00:17:30,080 --> 00:17:32,960 And some of those microbial reefs might again have a 291 00:17:33,320 --> 00:17:35,440 silicious sponge stuck here or there. 292 00:17:35,600 --> 00:17:38,800 But real animal reef building this takes a hit for about 293 00:17:38,800 --> 00:17:42,040 5,000,000 years. And what about the modern coral 294 00:17:42,040 --> 00:17:44,960 then that you mentioned that arose in the Mid Triassic? 295 00:17:44,960 --> 00:17:48,360 How did those fare with the various extinctions, in 296 00:17:48,360 --> 00:17:51,600 particular the one at the end of the Cretaceous that destroyed 297 00:17:51,600 --> 00:17:54,080 the dinosaurs? It's interesting once the 298 00:17:54,080 --> 00:17:59,120 scleractinian corals show up in spite of stresses of mass 299 00:17:59,120 --> 00:18:02,160 extinction. So they survived the Triassic 300 00:18:02,160 --> 00:18:06,080 Jurassic mass extinction and they survived the Cretaceous 301 00:18:06,080 --> 00:18:09,600 Tertiary mass extinction. They survived what we think is a 302 00:18:09,600 --> 00:18:12,960 a massive global warming event at the Paleocene, Eocene Thermal 303 00:18:12,960 --> 00:18:16,880 Maximum interval. So it is interesting that the 304 00:18:16,880 --> 00:18:21,200 scleractinian corals, not that individuals within that group 305 00:18:21,200 --> 00:18:23,360 might not have gone extinct because of some of those 306 00:18:23,360 --> 00:18:28,120 stresses, but in total those sclerotinian corals persist and 307 00:18:28,120 --> 00:18:30,000 are the ones that make our reefs today. 308 00:18:30,280 --> 00:18:34,200 And ironically, seem very vulnerable to what's happening 309 00:18:34,200 --> 00:18:37,720 to the planet right now. Unfortunately, yes, with the 310 00:18:37,720 --> 00:18:42,240 variety of stresses that we are causing, both excessive heat 311 00:18:42,440 --> 00:18:45,880 that the corals fare very poorly with excessive warm ocean 312 00:18:45,880 --> 00:18:49,280 temperatures because it's so deeply effects their symbiotes, 313 00:18:49,520 --> 00:18:53,360 but also with the acidification of the ocean with increased 314 00:18:53,520 --> 00:18:56,360 dissolve CO2 acidifying the surface ocean. 315 00:18:56,360 --> 00:18:58,840 It's another stress that corals are having to deal with. 316 00:18:59,120 --> 00:19:04,000 So the stresses that humans are inducing is palpable and has 317 00:19:04,000 --> 00:19:08,200 effects on these ecosystems. And it is, I guess, interesting 318 00:19:08,200 --> 00:19:11,280 and depressing to think about whether or not these 319 00:19:11,280 --> 00:19:13,720 sclerotinian corals will be able to survive humans. 320 00:19:14,120 --> 00:19:16,320 It's interesting because it's the stresses you describe that 321 00:19:16,320 --> 00:19:19,880 took place in geological time sound like they were at least as 322 00:19:19,880 --> 00:19:23,120 extreme, at least temperature wise, during the thermal 323 00:19:23,120 --> 00:19:25,360 maximum, pallocene thermal maximum you mentioned. 324 00:19:25,360 --> 00:19:28,120 But the rate of temperature increase was probably orders of 325 00:19:28,120 --> 00:19:30,720 magnitude slower, so maybe they had some time to adapt. 326 00:19:31,320 --> 00:19:34,760 That's one hypothesis is that the rate of change would have 327 00:19:34,760 --> 00:19:39,160 been slower. And then perhaps that was a 328 00:19:39,160 --> 00:19:43,400 piece of why the stress that we're seeing today is just so 329 00:19:43,400 --> 00:19:46,480 much more for the modern ecosystem to withstand. 330 00:19:47,320 --> 00:19:48,840 What are you working on at the moment? 331 00:19:49,440 --> 00:19:52,720 One of the reef questions that have been percolating since my 332 00:19:52,720 --> 00:19:56,200 dissertation, where I looked at some of those odd Lower Triassic 333 00:19:56,200 --> 00:19:59,640 microbial reefs, and then for my postdoc, bounced back to the 334 00:19:59,640 --> 00:20:02,680 Cambrian and started working on Archaeosiath reefs. 335 00:20:03,000 --> 00:20:06,720 One of the things that I've been thinking about is this continuum 336 00:20:06,720 --> 00:20:10,040 where you start with this Early Cambrian experiment in animal 337 00:20:10,040 --> 00:20:13,080 reef building, the topic of our podcast today, these wonderful 338 00:20:13,080 --> 00:20:17,160 Archaeosiath reefs, and then they disappear, and then what 339 00:20:17,160 --> 00:20:18,920 comes back and what does that look like? 340 00:20:19,440 --> 00:20:22,520 I've been really increasingly interested in this early or 341 00:20:22,520 --> 00:20:26,000 division interval of reef building, where again, there are 342 00:20:26,000 --> 00:20:29,080 enigmatic calcifying organisms that show up. 343 00:20:29,080 --> 00:20:31,800 People debate about what their exact affinity is. 344 00:20:31,800 --> 00:20:34,360 Are they sponges? Are they calcarius alga? 345 00:20:34,720 --> 00:20:36,560 Are they something different entirely? 346 00:20:37,240 --> 00:20:40,240 Watching them move into reef ecosystems and started to 347 00:20:40,240 --> 00:20:42,800 contribute to framework is really interesting. 348 00:20:42,800 --> 00:20:46,680 And what does that tell us about early or division ecosystems and 349 00:20:46,680 --> 00:20:49,600 oxygen and where animals are living? 350 00:20:49,640 --> 00:20:53,280 Does it again occupy the same kind of ecospace that it did in 351 00:20:53,280 --> 00:20:57,400 the early Cambrian, where they are providing a location and an 352 00:20:57,400 --> 00:21:01,080 ecosystem that allows other calcareous organisms to thrive? 353 00:21:01,280 --> 00:21:04,720 Or are they less important because perhaps conditions in 354 00:21:04,720 --> 00:21:08,240 the early or division are more broadly amenable to organisms, 355 00:21:08,240 --> 00:21:09,960 and so the reefs are a little less important? 356 00:21:10,000 --> 00:21:12,880 These are the kinds of questions my research group and my 357 00:21:12,880 --> 00:21:15,200 students particularly, are trying to untangle. 358 00:21:15,640 --> 00:21:18,120 Is it possibly one way of thinking about it a kind of 359 00:21:18,120 --> 00:21:22,640 example of convergent evolution where various very different 360 00:21:22,640 --> 00:21:26,480 kinds of animals have kind of reinvented the reef at various 361 00:21:26,480 --> 00:21:30,200 times during geological time? I think about it all the time. 362 00:21:30,200 --> 00:21:32,000 What is the advantage of the reef? 363 00:21:32,000 --> 00:21:35,040 What is it about these particular environments and 364 00:21:35,040 --> 00:21:39,440 these ecosystems that organisms from different groups have 365 00:21:39,440 --> 00:21:41,560 figured out how to do it over time? 366 00:21:41,800 --> 00:21:44,960 When you see something like that happen in evolutionary history 367 00:21:44,960 --> 00:21:48,040 again and again and again, kind of like the coiled shell, all 368 00:21:48,040 --> 00:21:50,680 the coiled shell must provide such wonderful advantages 369 00:21:50,680 --> 00:21:54,960 because things from aminoids to snails to forums have figured 370 00:21:54,960 --> 00:21:57,200 out how to do it. And we, you know, go do an 371 00:21:57,200 --> 00:22:00,040 entire separate podcast about the advantages of the coiled 372 00:22:00,040 --> 00:22:01,880 shell. But when I when you see things 373 00:22:01,880 --> 00:22:04,440 in evolutionary history that happen again and again, you have 374 00:22:04,440 --> 00:22:07,600 to think to yourself what an advantage it must have been for 375 00:22:07,680 --> 00:22:10,160 for animals to figure out how to make a reef. 376 00:22:10,160 --> 00:22:14,160 Because if these organisms are spending energy and evolving 377 00:22:14,160 --> 00:22:17,000 into that niche, then that means that there's some real 378 00:22:17,000 --> 00:22:18,800 evolutionary advantage to being there. 379 00:22:19,160 --> 00:22:22,280 And one can imagine that those environments, particularly ones 380 00:22:22,280 --> 00:22:26,320 that are as many reefs, are in high wave agitated settings, 381 00:22:26,320 --> 00:22:28,960 tropical carbonate settings. There's a lot of calcium 382 00:22:28,960 --> 00:22:30,720 carbonate around to make your skeleton. 383 00:22:31,120 --> 00:22:33,760 They might be particularly well mixed with oxygen. 384 00:22:34,320 --> 00:22:36,480 There's a whole variety of reasons to think that they were 385 00:22:36,720 --> 00:22:40,440 particularly habitable, but it is interesting that you just see 386 00:22:40,440 --> 00:22:43,200 it again and again. In spite of the stresses that 387 00:22:43,200 --> 00:22:46,760 have tried to take them out over and over again, Over time they 388 00:22:46,760 --> 00:22:50,840 reinvent this ecosystem. Sarah Proust, thank you very 389 00:22:50,840 --> 00:22:53,080 much. It's been a pleasure, Oliver. 390 00:22:53,080 --> 00:22:54,720 I'll come back and talk to you anytime. 391 00:22:56,120 --> 00:22:58,800 To see pictures and illustrations that support this 392 00:22:58,800 --> 00:23:04,080 podcast, go to geologybytes.com, where you'll also find a subject 393 00:23:04,080 --> 00:23:06,000 matter index of all the episodes. 394 00:23:06,440 --> 00:23:09,840 There you can also give me feedback which I welcome, as 395 00:23:09,840 --> 00:23:12,800 well as sign up to get my emails about new episodes.