 Welcome to the next stop in our 500 million year rapid fire tour through the evolution of animals getting up towards us. Well, we probably won't really have time to get up towards us, but we'll at least get up to the dinosaurs. That is my promise to you. So today we've got a lot of ground to cover, about 200 million years, or rather not actually a lot of ground, a lot of water to cover. So we might as well get started. If you remember where we left off last time, we started in the Edeachryan roughly around 650 million years ago with the very first animal communities emerging. And they're very strange things, many of which have no clear relationship that things are alive today. By the end of the Edeachryan, by the end of the Edeachryan, we get the first examples of skeletons being built, the first examples of predation, as well as examples of organisms moving around on the seafloor. So we've got motion, we've got things attacking each other. That gives rise in the Cambrian to a spread of biomineralization. More and more things start building shells, things start moving in more complicated ways. They start burrowing into the ground. And by the mid Cambrian, you've got a place that you would recognize as a marine community. You wouldn't recognize any of the individual things, almost nothing that existed in the Cambrian is still around today, at least in a form that's similar to what it was like. But you would recognize all of the classes of organisms, the groups. So this thing here is a giant swimming arthropod, but I mean it's playing an ecosystem role like a fish does today. And these things here are playing ecosystem roles like crabs today. Totally unrelated or largely unrelated, but they're performing similar things. You've got a similar kind of diversity of organisms hanging out within these communities. So not diversity in terms of number of species, but in terms of the occupants of different sorts of niches. This is a pretty fleshed out community, but not as fleshed out as a modern community as you're going to see in a second. So this is where we got up to. Right here is where we start building up, let me make a smaller line here. Right here is where we start seeing the very beginning of the emergence of animals. We've seen animals per se, although perhaps sponges back here, but certainly evidence of embryos and things like that. As we move through the Edeachryan though, we get the first animal community showing up. And then as we move through the Cambrian, of course, we've got that explosion in terms of the major phyla, the major groups of organisms. So what I'm interested in talking about today is this whole unit of time right after here, the majority of the Paleozoic. So this is what we are looking at. Here are the timelines. I haven't updated this. This is a time scale from a couple of years ago, so the exact ages are not quite right. I'm not going to ask you this anyways. I'm interested in you knowing what is happening in the early to kind of mid Paleozoic, what is happening in here. So that is what we are interested in. All right, this is what we are going to focus on over the next two lectures. So don't get freaked out here. We've got 12 topics. Sure, we've got two lectures to cover it. And I'm going to divide them roughly into not time intervals, but rather we're taking a what's happening in the sea versus what is happening on land approach. And so the goal for today is going to be talking about mostly the marine stuff, except we're going to save this thing over here, the Devonian extinction to next class. So let's get going. What's number one up? Number one up is the Great Ordovician Biodiversification Event, or the Gobi. So this is a continuation of the story that we saw in the Cambrian. In the Cambrian, we get the emergence of all of these major groups of organisms. So for example, here is the Maluska. What are the Maluska? These are everything today from squids to snails to octopuses, clams, all of those things are mullusks. So we probably have at least precursors of mullusks down in the Edeachryan. But the first really clear ones show up, the proper, what we'd call crown group mullusks, show up in the Cambrian. And in fact, all of these things, all of the major groups of life seem to have their first proper appearance in the Cambrian with the possible exception of one group called the Bariazoa, who might not show up until the Ordovician. So this is what's happened in the Cambrian, is that we have a huge increase in what we call disparity. For anyone who has been in biology, disparity doesn't mean to be sad. We're talking about the difference between organisms. So how different is this organism from this organism? So the broad groups are appearing. But the actual number of species that exist on earth are nowhere near in the Cambrian, what they're going to be in the Ordovician or certainly what they are like today. So that's where we are in the Cambrian. So the great Ordovician Biodiversification event then isn't the appearance of all of these major groups. Rather, it's an increase in the total number of things like species and genera. So if you guys want to read an overview, there's an article and all of these hyperlinks are going to be live in the PDF I put up online. This is a really recent overview of what's actually going on and how it differs and how it's a continuation of the Cambrian event. This is from a different paper, 2009 paper. This is running through. Here's the Cambrian, here's the Ordovician. These are family level, right? So this is quite a high level of biological classification. And what you can see, I've outlined the edge right here of the... I've outlined the edge of the Ordovician. Here is the Great Ordovician Biodiversification event. Let's make that a little smaller right here. And you should see that although we had a clear increase in the number of families go through the Cambrian, the rate of increase dramatically takes off in the Ordovician. And then note that it more or less plateaus all the way through until we get to this giant mass extinction event over here. And then a weird thing happens. After this giant mass extinction event, it comes back, it gets to the former plateau, and then it keeps on going until today. We'll revisit this portion of the story later on. But right now we're going to be talking about this portion, in particular this portion right here, the Great Ordovician Biodiversification event. All right, so here is what is happening. Here is your explosion of body plans. This is your disparity, your main groups appearing here. And then over here we've got an explosion of biodiversity. I suspect if I asked you something like contrast the Cambrian explosion, a Great Ordovician Biodiversification event, what I want from you in a short answer question is Cambrian explosion equals disparity. Right, so the main body plan showing up, Great Ordovician Biodiversification event equals diversity, total number of things like species and genera, massively increasing over here. And this is in the Ordovician. So here is the Paleozoic Plateau, and then you've got these extinctions. We're going to talk about these two extinctions now. Next week we're going to talk about these extinctions over here. All right, here is a diagram showing that really this event is not an event at all, in the sense that it is not a single thing. In fact it's made up of a series of major changes. So the first portion of it is this planktonic revolution. So you start getting a huge increase in the diversity of things floating up in the water column. These are the base of the food chain, the things that are going to support things like fish and giant arthropods. So they explode in diversity and abundance over here in the beginning of the Ordovician. And the cause of that isn't clear, but it's probably things like changes in ocean chemistry, oxygen levels, temperature, the total amount of sea level change, the amount of flooded platform areas. And we'll look at that in a second. The real increase though in diversity, you can see doesn't actually happen until we get to the middle all the ways over here to kind of the late Ordovician. And what you're seeing in here is an increase first in things like the organisms living on the bottom, so clams and their equivalent, more often things called brachypods, which are kind of the Paleozoic equivalent of a clam. And then reef communities over here eventually as actual proper reefs with real coral, those strange archaeocyathans, but actual proper coral takes off over here. So the first thing I want to point out is this is not really an event you can see here. This is a tens of millions year long, slow and progressive increase. Now on a higher resolution, you'd see that this is not a continuous rate of increase, that there are a series of kind of stops and starts, and it's debated amongst the community how much this is a series of discrete events, it's a continuous ramping up of diversity. That's beyond the level of this lecture, and really we haven't made up our mind as a paleontological community yet. But the bottom line is there is a dramatic increase throughout the Ordovician in the total amount of diversity going on. And it's at least partially caused by changes that are in the inorganic components of ecosystems, things like more oxygen, things like an increase in sea level, creating more habitat for things to live in, perhaps changes in temperature, all of that stuff is definitely going on and playing some role. But the majority of the story is probably just a continuation of what we saw in the Cambrian itself. Here is, this is reefs, and you can see there's the middle, really it's the middle and the late, is when we get the ramping up, we get some in the beginning here. That's this continuation of what we were talking about. So what is actually going on in terms of the organisms? You do not have to memorize these. I'm going to ask you some things about these main groups of organisms later on, but you're going to have a lab where you actually look at pictures and interact with models and things of these things. But there is this increase in diversity. A number of these guys are new groups, not in the sense that this is, these guys are the same group that includes things like starfishes, these are the kind of germs, but crinoids proper don't exist until we get into the Ordovician. Things like Graptolites, that we have primitive versions of them back in the Cambrian, but the ones that are floating around in the water column become really important. They don't show up until we get into the Ordovician. So we get a number of these things here, particular representatives of things that if you look at any rock, really through the Paleozoic, you're going to find representatives of these things. These are different kinds of critters in terms of the specific families in that than what we saw in the Cambrian. So they're a continuation, but they really are, they look different. If you look at a community from the Cambrian, it is different in terms of who occupies it than the ones in the Ordovician, the Silurian, the Devonian. The other thing though is that these guys are just much more complicated. The things are bigger, there are more complicated ecosystem interactions. This is a whole different environment, both in terms of overall what's living in it, but also the complexity of the interactions than the Cambrian right here. So you see things like this, and you don't have to know these particular organisms. These are Brachyopods, they look like clams, they're not actually clams. These are Bryozoans. These are actually related to Brachyopods. You can find them at you today. If you go up in Nova Scotia anywhere, you find seaweed. Pick some seaweed up and look for seaweed next time you're out for a walk that has kind of white patches on it. If you look really closely in the white patch, you'll see that there are these little kind of divots growing on there, this kind of calcareous material. That's actually an invasive species. It's a form of Bryozoan, I forget what it's called, and each one of those little pits that you would see would have a tiny little filter feeding organism on it. So these guys were major components of marine systems in the Paleozoic. They're less important today. Crinoids, these are essentially giant stocked starfish, starfish sitting on big towers like this. I mean, not literally, they're relatively closely related. Corals, the proper first coral show up in the Ordovician. And there's the two big groups I'll show you in a second. These things are consistently throughout pretty much the Ordovician. We see these things until we get to the, sorry, throughout the Paleozoic until we get to the Devonian. And these are the two big groups. Anytime you pick up really any limestone environment in the Ordovician, you're going to find one of these things. I have bags of them in my, in the lab. You can come by and, I'll probably even give you one if you come by and you're nice enough. The Graptolites, these are the area that I studied. Okay, so what's driving this stuff? Again, it's still an open question. We've got, this is a diagram showing here's your increase in diversity and we've got things like, notice that although it is overall, this is Greece Celsius, overall it's quite hot throughout most of the the Ordovician, right? There is a steady decrease in temperature and that decrease in temperature correlates pretty well with this increase over here. So maybe there's some kind of climate driver on diversification. You know, this is a suggestion that, that climate driving, this dropdown here is maybe being driven by an increase in, in dust from this major breakup of a meteorite. There's a bunch of these arguments that are going on. I'm not super interested in trying to dissect what are the geochemical or climate kind of triggers pushing these because those are contested, they're also less important ultimately than the ecological interactions. So really what's going on here is a story which is a continuation of what we talked about in the last class, which is that as organisms show up, they drive diversity. So more species equals more species. And how does that work? Because these guys are modifying the environments. They're modifying them both by physically changing the environments, doing things like building physical substrates that things can live upon. So now you've got a hard environment, a coral reef, that also changes how waves interact with the shore because reefs act as wave breaks and that creates quiet areas behind them that other things can live in. Things that are going through and recycling, that are recycling material which is coming out from the upper parts of the water column, little fecal pallets are coming here and they're coming down into the benthic realm, they're coming down into the ground and they get recycled by scavengers and all of these interactions between these various things create opportunities for specialization. And they literally are changing the physical environment but also in their interactions together where one thing is eating another thing specializes so it doesn't get eaten and then the thing that eats it specializes in eating it to the point where you just start driving through this hyper specialization you start driving diversity. So this is the same kind of story we talked about last time where more diversity begets more diversity. A spiraling kind of a spiraling pattern of complexification of ecosystems driven by the organisms themselves. That is probably the largest thing that's driving this this Ordovician event. And this is a continuation then really of what we saw in the Cambrian if you think about it in that way. So you can see this same kind of pattern we saw where we had organisms getting larger and reaching up, swimming up into the water column but at the same time burrowing down deeper into the substrate, therefore bringing oxygen with them that continues on where things get bigger, they're swimming around more but they're also burrowing down into the ground more. You can see this actually in the organisms themselves. So we've got things like these crinoids here and they get big. Some of these things are getting pretty close to tree size. They're getting 10 feet tall. Here's an example of my favorite big organism. So remember that in the Cambrian the largest organism was Anomalycharis here. This is a 1 meter long swimming bug. This thing on the other hand, 7 meters that means this thing is about 20 feet long. This is an orthocone, and it's essentially a giant squid that lives inside of a shell. The Nautilus, you've probably seen Nautilus shells for sale. The Nautilus is the only living relative of these things, but they got massive in the Ordovician. This is a quick little video here, reconstruction. These are Eryctorids. These were other swimming arthropods from the Crawling and Swimming Arthropods from the Ordovician, and here is a reconstruction in CGI of the giant orthocone. This is a fun video. This is made by the BBC. It's called Swimming with Sea Monster or something like that. Someone with prehistoric beasts. Here he is cruising along. There's Eryctorids on land here. Anyways, you can check this video out, but it's pretty fun. This is a big creature is the point. Here's some more Canadian Biggest. There's a lot of Biggest Firstists. We've got a lot of Estists. This guy here is the largest trilobite known. It's from Northern Manitoba. If you want to see it, it is in the Royal Ontario Museum. There's three quarters of a meter long. This is two plus feet long. This is a really large organism. Given that these things are normally a trilobite is as big as that scale there. This is a huge organism. It gives you an idea what the ecosystem has to be like to be able to support these things. This is maybe my favorite example. One of my favorite examples of big things. You remember Anomalychorus? There was a predator here. He's a super predator. He's got that big, scary mouth. It's called a patoya. I'm never going to ask you that, but if you want to know. This is another Canadian find. Actually, maybe it's from Greenland. It's an Arctic find. This thing here is a modified version of that appendage there, which was used to grab organisms. Except if you look at the fine details of this, and there's the actual fossil itself, what you see is these are little hair-like filaments that would be useless for grabbing, say, a trilobite, but would be great for sweeping through the water and grabbing plankton. This guy here is an example of an early filter feeder. Let me show you. Is this Ordovician monster over here? I love this next guy. This critter here, and if you click this link again, you can see this is a two meter long beast. If you look down here, this apparatus, there's the actual fossilized version of it right there. There's the fossilized version. These little hairs that are coming off this thing is functionally exactly the same as Baleen. So there's Baleen, which is what's inside a filter feeding whale, something like a humpback whale or a blue whale. They have this Baleen structure. Look at the structure of this thing here, and look at this thing here. This is how it would have been arranged in life. So again, these things are completely unrelated, but it's a fantastic example of convergent evolution. This thing is from Moroccan. It's an early Ordovician creature. It's something like Egyro-Cassus Ben-Moli. Ben-Moli is named after the Moroccan man who actually found the specimen. Anyways, I love this beast. You can click on the link if you want to read more about it there. Alright, so let's move along to point number two, which is the evolution of reefs. So you remember that when we were in the Cambrian we get the first kind of substrate building organisms in the sense of we have things that are building really small mound-like reefs, the Archaeocyathans. Well, real reefs take off in the Ordovician, and they reach their peak in the Devonian. So if you look at reefs today, I mean this is the Great Barrier Reef all along the edge here. This is something you can see from outer space. So you remember though that in the Paleozoic, huge parts of the world's continents were functionally covered by water, which meant that these kind of reef communities were capable of moving all over and you could build reefs up over here. In fact, we had carbonate platforms with large scale reefs covering large portions of the continents. I mean these are, they were producing reefs on a scale that just don't exist today. And I'll show you that in this image right here. So this is a shot from the Rockies in Alberta. This entire, let me just highlight it for you here, this entire structure you see right here, let me go back, this entire structure you see right here is a giant reef mound. And this is the kind of thing you might get in the Bahamas or something now. I mean this would be an island sticking out of the water at some point, not sticking out of the water like that, part of it sticking, you know, shallow in the water. Anyways, this just gives you an idea of the scale of these reef complexes that are forming in the in the Ordovician beginning, but hitting their kind of today in the Devonian. So if you look at this diagram right here, if you look at this diagram right here, here are the beginning, these are our Archeo-Syathans here, the beginning, these things are not really true reefs, the reef mounds, and then coming in the Ordovician we have this expansion reaching its maximum, literally in all of history, its maximum point during the Devonian. And these are made up of of Stomato-Poroids, but most importantly, they're made up of Corals. Made up of Corals. And if you are collecting fossils in any, really any locality in in the Ordovician, Cylerian, or Devonian, you can find things that look really similar to these fossils right here. These are chain corals, these are the most common, most kind of characteristic example of the group here, the Tabulits corals, or the Tabulata, and then down here are the Rugosins or the Rugos corals. And they are most characteristically formed by these things that look like this, they're called horn corals because they look like the horn of a sheep and they've got these, you know, radiating SEPTA that look like spokes of a bicycle inside, you can see right here there's the SEPTA right there. And then here these are the Tabulite corals oh sorry, this is the Tabulite corals. If you were to see a cross-section of one of these, what you would see, if this is the top, the opening here is you'd see they have a series of these almost like platforms in them which are called Tabulata, you can see them inside. Anyways, that's beyond what you really need to know for the, in the lab I'll have you look at that stuff, but anywhere you go you're going to find one of these guys or something that looks like this, if you're looking in kind of limestor in the environments. These things were super abundant, super prolific. So this is the age of the reefs really. Alright, point number three, high sea levels, abundant black shales, and these are interrelated ideas. But when I say high sea levels, I mean really high sea levels. So most of the paleozoic or at least kind of the early and mid paleozoic, sea levels are relatively high. Right here is a sea level curve. Right, we're down way over here now. As well as as well as temperatures are relatively high. These are obviously interrelated because if temperatures are really high then you've got no ice caps. Where does your ice go? Well the ice goes into the water, which is going to raise the sea level. But the other component of this is that you've got active tectonics which are driving this. Remember we already talked about in class on a long term when you've got rapid sea floor spreading, the ocean floor literally floats higher on the mantle and that forces water up onto the continents. The other thing is that when you smash plates into each other, you build mountains. You've got these orogenic events. And those mountains are necessarily higher than the flat ground was before tectonism. So where you've got active tectonic activity going on it can either cause when you've got subduction material to rise up out of the water or alternatively if you don't have any subduction going on then it's going to cause but you've got lots of spreading going on as these things are moving apart. This is a plate and they're moving apart like this. They are going to be relatively young because the lava is forming new rock right in the middle of the ocean here and this whole thing is floating up higher relative to the surrounding relative to the mantle or relatively what it would be when it's old and that's going to cause then if it's sitting up higher it means that the average depth of the ocean is going to be lower and that's going to force water up onto the continents. Anyways you've got these flooded continents I mean really flooded continents and so as a result you get these widespread deposits of largely what we call platformal sediments and a lot of these are going to be limestone these are going to be carbonate sediments. If you guys have been to New York state or you've driven through Ontario and you've seen the side of the highway most notably kind of around southern Ontario the Kingston area is really obvious all around Belleville if you know that area all of the sides of the highway as you drive through you're going to see of these stacked layers of kind of light gray rocks get out of your car I mean don't stop on the highway but if you get out of your car and take a look you're going to see that they are full of all of these organisms I was talking about earlier on this stuff we saw up here all of these creatures we saw where are they all of these creatures we saw somewhere these things all of these things you're going to see these things all just popping out of them massively abundant okay so this is what the sea levels would have looked like as we moved through the Cambrian right we had still large portions of this is just showing North American continent it's not showing the other ones over here remember we're calling this Laurentia right now and so here's the Cambrian we've got parts of it flooding notice this thing over here dashwoods and we'll talk about this later on this is a you know you've got active subduction going on this is being brought closer to the mainland over here now when we get to the Ordovician we've got this is the late Ordovician in particular we've got most of large parts of the continents covered in shallow seas and shallow seas and these are going to be hot seas as well reasonably hot seas the shallow tropicalish seas these are fantastic environments to build up diverse fauna corals and you know trilobites all of these kinds of things this is the Silurian we're losing some of our oceans but we've still got a lot now I'm going to notice over here here's some foreshadowing over here notice that where did our where did our dashwoods go well our dashwoods has accreted it's slammed onto the side here I notice what's coming along here look at these words Ganderia, Avalonia, Maguma we're going to come back to these guys in a second so I skipped by it but I want to go back to this slide this is a paper by Murphy and Nance on the Atlantic the CBC video you've met both of these characters Brendan Murphy is from Santa Facts he's got the giant hair and the giant beard anyways this is a paper they did on the breakup of continents but what I wanted to show you here is their correlation of rifting so breaking up of continents and subduction and how they're correlating them here with the sea level curve I also wanted to note the seas being relatively high throughout the entirety of the Paleozoic this is the Paleozoic here this is the boundary between the Paleozoic and the Mesozoic and then a progressive increase back up over here in the Mesozoic but you can see that there are points where it's moving up or down but otherwise we've got relatively high but correlating with what's happening on a tectonic level so that's again a theme that we visited earlier on let's move on beyond here here is our story so we've got again mostly flooded continents the other thing that's going on is that because the because the oceans are relatively hot because they're relatively hot we don't have the same degree of circulation that we used to have or we currently have in the oceans which brings you know oxygen rich waters from the pole and sends them down and you know these giant circulation belts that we're talking about and so during the Ordovician we had large scale intervals during the late Ordovician and actually the Silurian in particular as well we had large intervals where large portions of the deep waters of the oceans became anoxic and built up black carbon rich sails whenever you have black carbon rich sails on a widespread level globally that's telling you something super weird has happened what we call the global anoxic event these sails that we're building up are evidence as well that we've got something strange happening in terms of the world's oceans and it's related we think in large part due to these high temperatures also potentially to nutrient flux due to the evolution of really simple plants and I'm going to circle back to that idea later on so here's the Devonian and you can see what's happening the Devonian right well now we've got big mountains these are the Appalachians these would have been like the Himalayas at the time a huge portion of the earth is actually getting exposed over here now as we start to jam more stuff and build big mountains over here we still have relatively deep relatively deep ocean certainly in comparison to day so we have the Prairie provinces most of the interior of America would have been underwater and so you still find Devonian fossils marine fossils all through the states all through large parts of Canada as well and then suddenly you get this and this is going to be next class serious foreshadowing here as well and these guys are also going to be foreshadowing for a couple of classes from now remember those names I'm not going to make you see them on a test but the story I will ask you to tell me so by the time we get to the Carboniferous we've lost this ocean entirely but we've also simultaneously lost most of the ocean that used to cover the continents these are very different worlds this world and this world here are very different worlds and as you can tell by the coloration that they've done here that green arbitrary the world has really fundamentally changed in an important way that's foreshadow coming back to that but I want to now just move on and just talk quickly before we go about black shale so this is a paper that actually my supervisor wrote Dr. Mike Melchin at St. Effect's each one of these black spots here is an area where you have marine or where you have black shales this shot here number five that's actually my thesis locality up here and you can see it's retaining them to some degree the white spots here these are areas where you're getting relatively oxygen-rich environments and so what you can see are these widespread anoxic localities and then as we move into the mid-hernation that is the latest part just about the latest part of the Ordovician you can see that they've all switched into oxygen-rich environments and then look what happens this is the early Silurian the next period they've all flipped back to oxygen-poor environments this is a really important story we're going to talk about in a second but I do want you to notice especially in the Silurian look at how widespread these low oxygen deep water environments are and these are the kinds of rocks that are being produced in here so you can see alternating these are limestones those are alternating environments we've gotten you know short-term climate or short-term ocean changes where you've got you know more oxygen-rich stuff be deposited but in between these thick layers of black shales these represent oceans that have gone completely stagnant and they weren't universal I mean you still had environments we had lots of coral reefs and stuff but they were much much much more widespread than they were through most of Earth history especially in the Silurian and there is quite literally nothing like this in the Earth today some areas like the Black Sea you get kind of microcosms of it a little bit but on a broad oceanographic kind of scale this environment here with these widespread anoxic low oxygen conditions producing black shales these don't exist anymore this is a particularly weird thing that happened only a few times in Earth history the Silurian and the late Ordovician are a couple of the main examples we're going to add this in as another thing along with these shallow water seas the fact that the seas in some areas were completely stagnant on a global level and not all of them but in some environments especially off the coasts of continents were completely stagnant and devoid of oxygen that's another really weird thing that's going on okay so the final this isn't the final this is the the next kind of thing in the sequence is the late Ordovician extinction event so this used to be called the hernation extinction event but now we understand it better we understand it actually went over a much longer period of time so we switch the name to the late Ordovician extinction event you sometimes see it just written out as the loam or the loamy I don't even know how you'd say that so what is the late Ordovician mass extinction event well there are roughly one two three four five of these crazy mass extinction events that have just decimated marine largely marine but in some cases also terrestrial faunas so we're going to look today at this one here right the late Ordovician extinction event next class we'll talk about the Devonian and then we're going to round the class off by getting into these big extinction events so extinction is not is not odd in fact extinction is the normal pathway the normal endpoint of every species and every species that will ever exist will eventually go extinct including us eventually so there are lots of points where the earth has gone through serious environmental crisis and it's lost things like 20% of species we're in the middle of a serious environmental crisis right now but these ones here are events that stand out from all of that background level even the periodic massive climate and you know ecological upheavals that happen these ones are still crazy outliers these ones we're talking losing things like 80 plus percent of species this one here in particular we lost probably over 95% of species on earth these are huge events so the actual magnitude of these things is a bit debatable I'm going to use this estimate some people say this is an overestimate of about 80% of species lost during the late Ordovician extinction event and we understand the overall story pretty well of what the cause was so the cause was definitely not you know this is supposed to be a meteor coming in streaming in and blowing stuff up right that's probably or maybe the cause over here for this one but it's not a good not a good explanation I'm going to get rid of it for any of these ones over here instead we're pretty confident that this one here and actually probably this one here as well we'll talk about that next class these things are caused by climate change and in particular cooling followed by warming so this one here the Ordovician is a two phase extinction so it's actually prolonged over a period of several hundred thousand years at very least and we go from a globally warm environment to rapid onset of very extreme glaciation and with that comes a whole series of effects well if you're building up ice sheets on in this case the southern pole on a giant continent we call Gondwana where does that ice come from well that ice comes from water that evaporates and never makes it back into the ocean which means that the sea level is going to drop and it drops somewhere on the order of about a hundred meters dramatic drop in sea level and so that means that those shallow seas all over the continents they are going away and with them everything that used to live in them the other thing that's happening is that water is getting cooler and so things that are not adapted living in cool water they're going to go extinct but weirdly as we kick in ocean circulation so as we cool the earth we start getting these big convection cells where we are bringing you know oxygen you're bringing O2 from the surface this is water and you're taking it down into the subsurface through these big convection cells at the poles where it's cold coming all the way down like we talked about that starts breaking up those weird stagnant seas I was talking about and that's good if you're something that lives in today's oceans but if you're something which has evolved to live in a weird stagnant sea then changing it to an ocean which is more like today's ocean is going to kill it so this is a really important point to go back to remember we talked about evolution when we talk about fitness we do not mean some objective standard we mean the thing that is best able to survive in the current condition and so if you were able to live very well in a low oxygen environment and suddenly it become an oxygen rich environment you're dead another important thing we think happened is that more nitrogen became available and that meant that the phytoplankton shifted from ones that were dominated by blue-green algae or cyanobacteria to ones that were dominated by more traditional actual algae and everything that ate them then changes it's like we just destroyed all the grass and we replaced all the grass in the world with something else pine trees or something well something can eat pine trees but not the same thing that was eating grass and then when we get to the second phase of this two phase extinction we flip back to what the conditions used to be like and that means that all the species that have evolved now to live in these more circulated oxygen rich environments these colder oceans suddenly plunge back into warmer more stagnant oceans and they go extinct so you get extinction on both end both during the cooling interval and then in the subsequent warming interval afterwards so what is ultimately causing this glacial event and then the flip back to warm conditions we don't really know so it definitely involves a drawdown of CO2 just like adding CO2 is going to cause warming but whether that's the result of the ocean right so the weathering of silicates whether the result of the weathering of a large igneous province whether it's a result of enhanced weathering on the surface and fertilization of the ocean from first land plants we don't know these are all still open questions and you guys can switch into paleontology and work on the job here we're not done it's a big argument that's going on so we'll talk about this one in a second this one we're going to talk about next class alright let's move on to the next slide so here is a moment for digression I was going to talk about my own thesis for a second so this was my thesis was on the Ordovician mass extinction event if you guys want to destroy your minds or enlighten yourself you can read my horrible 600 page theses over here but I wanted to show you how we actually generate this data how do you make these stories my little tiny contribution to the story well here are the creatures I study so these are things called so these things are living up in the water column and they're living in a relatively low oxygen environment they're also adapted to relatively warm conditions these are the things that show up in the middle of the mass extinction event and they take over the world and these things used to live up in relatively colder water higher north, higher latitude conditions and so you get this migration that happens with these things coming down we also think these things might have been adapted to live on the kinds of organisms that live in potentially more potentially more kind of oxygen rich environments so you've got a shift in the kinds of organisms that are occurring and then after the mass extinction these are the things that evolve to take over the rest of the world if you want to read my thesis you can go through it in more detail but I wanted to show you how we generate this stuff so here is where my location is this is where I did my field work I spent two summers up here this is the Yukon Territory way up here this is Dawson City, Jack London White Fang famous gold rush city I'm way over here and this is in the middle of nowhere you can see there is even from space here there's no habitation almost at all here so this is helicopter ride actually there's a highway that goes up here beautiful highway that demonstrates you drive along it you'll know where this is my field locality the only way to get in here is by helicopter or by canoe or if you're me my first year I went in well I'll show you so here's the airport this is the Dawson City airport it's just this one building this is the baggage claim area this is where you drop your bags off this is how we got up to my field site my first year I hitchhiked up and I got a ride just by coincident with David Suzuki's son you guys know what David Suzuki is and I built myself a little raft and I floated down the river don't do this for field work look at the backdrop here you see that white color those are carbonates so I told you that we had a lot of shadow water limestones we also had a lot of black shales depending on where you were on the earth in the Ordovician you can see this right here in the background there's my boat the second year there's my field locality I'm coordinating black shales and limestone, black shale and limestone so these are probably short term very small flips in climate maybe orbital changes those sorts of things going on but this is what all of the rocks are looking like this is classic kind of Ordovician strata here's your limestones your carbonates and here is my locality this is my field assistant at the time this is Allison Atkinson there is the boundary red up here of the Cylurian that's the base of the Cylurian this is the important thing I wanted to show you there's my field assistant Allison and here is the black shales moving up through as we go through the late Ordovician and then right here this transformation to limestone is telling you two things it's telling you that the ocean has warmed up and it's also importantly telling you the sea level has dropped a lot and so that boundary right there is this late Ordovician mass extinction related dramatic drop in sea level it's recorded and it keeps on going up here is all limestone until we hit this kind of point just a little bit below here where it flips all the way back to black shale and these are these weirdo Cylurian black shale conditions so you go along like this where it's like black shale, black shale, black shale, black shale then you should see the color shift right in here this is the shift as the sea level drops things warm up you go to carbonate environments and then all this is black shale again this is all this strange environment so here we go from these oxygen poor conditions flip through this is the dramatic glacial interval right here and then we flip back to the oil conditions so we had extinction right in here and then we have extinction again right in here again really hardcore extinction this by the way is what the end of that field season looked like so this was another, it spent me almost 10 years I spent almost looking at these things under a microscope and this is the story here at the end result you can read the paper this is one of the papers that came out of it this is not just my locality it's a survey around the world and here's these are species diversity moving through and you can see we go up and that's the mass extinction event just a dramatic drop down to essentially essentially no species left this is a paper that came out in 2015 I just wanted to bring it to your attention because I wanted to show you what's going on here this is the latest or division moving up here this here each one of these this is sea level right so this is this is sea level where you've got sea level falling, sea level rising sea level falling, sea level rising sea level falling like this jumping up and down as these ice sheets are building and going back and forth and this is the really big one this is the one that that really hit things hard that where we flip into the limestones that one where I was showing you that's this interval right here but I wanted to show you this over here you see these little numbers going back and forth these are Milankovitch cycles and what I wanted to show you is this correlation between sea level rise and fall and the Milankovitch cycles themselves so these Milankovitch cycles are remember always there they're always there these are these orbital force cycles we talked about and we talked about climate change they're always in the backdrop but just like in the last or last ice ages once you get the world to shift into cold conditions then often you can see them and you get these periodic drum beats of ice age interglacial ice age interglacial ice age like this and this was the most dramatic of these ice ages so these aren't forcing us into cold conditions something else has forced us into cold conditions but once we get into these cold conditions then these oscillations of those various Milankovitch cycles are causing short term you know relatively moderate back and forth back and forth back and forth right they're causing that glacial interglacial cycle I just wanted to point that out because it ties into what we were talking about way earlier on in the class okay so what is causing this so for if you ask me in 2017 what the cause of this was notice 2017 also notice these are two totally different research groups that are publishing in essentially the same month in two very high high profile papers in two very high profile journals anyways here we go a volcanic trigger right mercury spikes to a volcanic driver so what was the story with snowball earth think way back to snowball earth remember the story with snowball earth was largely was partial to the breakup of Rodinia but also is that we had this large igneous province the Franklin large igneous province which really rapidly weathers so as it rapidly weathers it's going to use up and bind up co2 so that was the story for snowball earth let's call it se here snowball earth so for other mass extinctions we'll talk about in a moment there was nothing around during here really nothing nothing seriously of no animals or anything killed during the Franklin one but the idea is maybe there was a large igneous province which was forming rapidly weathering and that caused a minor version of the snowball earth event and he didn't actually cause a snowball earth event but it caused catastrophic global cooling well the question is is there any evidence of a lip and there isn't in terms of actual volcanic rocks we're talking about 450 million years ago so what are the odds if this stuff's weathering so heavily away that any of it was preserved so the fact that we don't have any of the rocks left doesn't mean the rocks were never there so this is another example of why so much of what we do in geology is one step removed from the actual evidence we look at proxies so in this case what they were looking for is they were looking at mercury in sediments being deposited in the oceans and they came to the conclusion that there was a giant spike in the amount of mercury and the mercury supposedly was being released as this large igneous province weathered so the mercury is coming out of this and going into the ocean right the mercury is going into the ocean there's my mercury there going into the ocean and so even though the large igneous province is gone we can still find evidence of it in the form of this enriched amount of mercury so this was a really good argument it seemed to be and this was suddenly it was a satisfying conclusion to what is causing this as you'll see in a couple of lectures we've got evidence of large igneous provinces causing mass extinctions in other localities so this seemed like a pretty slam dunk story the problem is that just last year this new paper came out and we'll see what happens in the papers that come after this they looked at this data again and they said hey yeah that mercury is there but when we control for another factor we find that there's no correlation anymore so remember this is the problem when you're using proxies for something in this case you're using it for weathering so they're saying no that mercury apparent mercury anomaly it's not actually a real thing that yeah there's more mercury but that's because these black shales some of these ocean environments they had more less sulfides in them and the mercury was actually getting attracted to this and so the real thing that was changing was just the amount of this material that was in the sediment it wasn't the amount of actual weathering that's their argument so we'll see what happens but when you take into account this the amount of sulfide material that's in the sediment suddenly that whole anomaly disappears so that story which was so great seems to have disappeared but it could well still be that this is the cause of it that it's a lip which is weathered totally way if the lip doesn't stand up and it looks like maybe it won't then we're back to things that we were looking at in the very beginning we're back to things like things like maybe it's the plant will tell you that story or maybe it's mountain building we don't really know alright so that is the or division mass extinction event a two-stage extinction caused by a rapid shift in climate first to cold conditions and then back and that's the that's the ultimate driver the immediate to the the immediate effect was things like changes in ocean chemistry cooling you know loss of an oxy zones or then the the creation of an oxy zones training of continental seas those are the immediate effect of the long-term thing causing all of this was climate change which was caused by well we're not totally sure alright now let's move on to number six I've jumped out of order here and I want to talk about the birth of the appellation so we live in the appellations if you go to the highlands that's part of the appellations the very most northern bit so the appellation mountains now are you know relatively low-lying hills but if you were to go back in through the Ordovician and Devonian they would have been Himalaya style giant mountains they have just weathered away right they've been slowly weathered down to their current position so let's talk about these guys because this is our own backyard this is what we're living in right now this is a great diagram from that book I put in your syllabus is a recommended reading this is the four billion years and counting and it's full of awesome diagrams and again they're freely available if you want to use them for projects or teaching so this diagram is showing continents and as continents each one of these continents is color coded so here's Rodinia supercontinent these two big continental masses joined together and here they are splitting up and going on different journeys so it's showing you the further apart each one of these each line represents a continent the further apart they are right the further geographically they were parts you go across here and there's that breakup of Rodinia when about 750 million years ago then they came and they started cruising back together and look over here around 350 million years ago we build the next supercontinent Panjia but what I want to show you is when they start slamming into each other like this so here's the Cambrian here's the Ordovician and you see during the Ordovician we start slamming things into this is Laurentia this is North America this whole color here is North America along here and we start slamming things into the side here and start building a little bit of mountains the beginning of the Appalachians here and then we start hardcore building the Appalachians as we move through the Silurian and the Devonian so that's going to be the story so there's our Rodinia is a story of breaking up and then there's a story of everything coming back together collectively and that's going to take us into not just next lecture but the lecture on that is going to be that real story so you can see the story on Google Maps if you look here you should be able to see that there's an overall kind of sequence of linear features you can see from a map level if you've ever driven through this you'll see that this whole thing is a series of ripples that go back and forth you've got your little car and you're going to go down a hill and up a hill I just about destroyed my car driving through the Pennsylvania and you can see that all along there why is that the case that's because the coastline is made up of a series of continents little mini continents that got slammed on to the side and just like a car slamming into another car causes the causes the hood to rumple up this is causing the continent to rumple up to literally to form and fault and create these linear patterns here so you can see this entire portion of the seaboard this entire portion of the seaboard here actually came from away so you know if you're born in Cape Breton you might say that I am a come from away but I would say you know what Cape Breton itself is a come from away this whole thing is a CFA right this whole thing is a CFA or come from away right boom okay so let us move on and talk about these components if you look at a geological map of North America sorry of Nova Scotia what you will see is that they seem to be almost two different things the kinds of rocks you get up here are totally different than the kind of rocks you get down here and the line of transition is right around Truro that is because these are literally two totally different things and in fact this thing up here is two different things as well you've got one thing here another thing over here and another thing over here and we talked about Gandaria Avalonia Maguma well guess what we've got here guess we've got here Gandaria Avalonia Maguma let me show you this so we'll move on down here this is another map this comes from Sandra Barr and Chris White and this shows you that these features which were slammed on to the edge sequentially they actually continue all the ways along so if you look at the rocks right here you know in western Cape Breton these are actually the same kinds of rocks you see all the ways along here they continue to Newfoundland and they actually continue all the ways over to Scotland and Ireland you can find exactly the same rocks they were all one continental landmass a long skinny thing something like Japan or Indonesia that got slammed on to the side of of North America so it got slammed on and then this component got slammed on all this green stuff here so this green stuff that makes up a good chunk of remember this is called the Avalon Peninsula so that's where we get the name from this is the Avalon terrain all of this is the Avalon terrain you go down here this is the same stuff these were all one geologic unit and then finally the other part here which is called Meguma you go to Halifax the rocks down here are not only totally different they formed in a totally different part of the world so let's look at their story very quickly here is Laurentia and the Cambrian there's the Dashwoods this is this first component it makes up part of kind of Pennsylvania and all this material along here it comes on it slams on to the side building our first mountains around the Ordovician land area coming cruising along off shore over here you've still got Avalonia Meguma they're coming here they go here they come and I'm going to note this reconstruction this is a it's not a guess it's it's one argument exactly where these things were relative to each other this is still an area of hot scientific controversy right things get hot right they get they get heated right I mean it's it's in good it's in good fun but they really are this is this is controversial stuff so we know they came from somewhere over by where Africa was at the time we think and they came sequentially slamming into the side so here they come and this is what it looks like afterwards where they all came in and by the mid-divonian as they slam and they're building these giant mountain ranges so here is the old ancient you know paleo Appalachian side this Himalayan style these things would have been like Mount Everest stretching up all along here and here they are in kind of diagram form this is from Sandra Barr so here's Ganderia right so this is the western side of Cape Breton here is Avalonia this is the eastern side of Cape Breton and then here's Meguma and they're slamming on this is North America over here they're all coming they're gonna slam along this is where they formed this is this one model of where they formed off of what eventually becomes Africa and here they come they're on their journey this is where they're forming off the coast of Africa and they all come across is subducting at the same time as an ocean is forming over here over here so you've got seafloor spreading happening here and you've got subduction happening here so this whole thing is disappearing with the end result this gets slammed on to the side really don't think about this driving along like a car this whole thing is a conveyor belt it's all moving because underneath this ocean is rock it's conducting or subducting underneath as well and here is a step-by-step thing showing the accretion of these components all right cool here by the way is a map this this paper was only looking at this component of it here so everything I'm gonna get my pen I'll get my pen here all of this stuff over here almost all this stuff over here this is what we call Ganderia with the exception of this bit here if you ever go to Pulitz Cove around Cape North right this kind of this little bit here this is the oldest part of all of Cape Retin this is a component of the ancient coast of North America this is the only part which is actually a native part of North America everything else came from away everything else came slamming on the side afterwards and this stuff is about 1.5 billion years old is how old all this stuff is the rest of the stuff in here is kind of like 650 million years old ish that kind of stuff and it all came slamming on to the side you know between about 450 and 350 million years ago this paper is only looking at here so there's no detail about these sides but I want to show you all of these blobs of granite and diorite in here if you've ever driven around Ingenish you know it's all beautiful granite well where's that granite coming from we'll think about subduction we talked about this in lab subduction causes volcanism right so here's your mountain your volcano forming and the heart of that volcano the bottom of it that's your granite forming down here so this is all caused by subduction as well this is kind of a monotonous subducting they're causing giant volcanoes all along here and these are just the bases of the volcanoes the volcanoes have been long since eroded away but you can see their bases there so as you move along and go on this summer and check out the Cabot Trail think about the fact that you're standing on totally different parts of the world when you are here or here or if you hike the Pulitz Cove totally different parts of the world now as you're checking out you know you go to Green Cove and you check out what you're looking at the Highland Lodge you see the granite there you're looking at you can actually go up and touch you know the bottoms of volcanoes that were forming hundreds of millions of years ago as this massive continental collision took place okay that's all we're going to talk about with that well actually no one more thing so this is if you go to Newfoundland you can see again as we're building up mountains what's going to happen those mountains are going to be eroding and you're going to have you know sediment mountains it is going to be it's going to be shedding off and so these guys here are underwater deposits of material which is building up as these mountains which are being massively rapidly built up they're also rapidly eroding and so this is these are oceanic sediments being built up off the course made up of eroded bits of those ancient mountains and you can see them also as they got slammed together they got tilted up remember principle of original horizontality if you find rocks that are vertical like this you know they had to have been slammed and tectonically deformed well here they are flipped up on their side this is St. John's right and you can see these things are essentially vertical over here this is another part of New Brunswick and you can see them all messed up like this that's because they've been squished seriously put in a tectonic vice okay that really is all I'm going to talk about here so let's move beyond this and we'll talk about one final idea which is the origin of jaws so I mean the movie jaws that has its own cinematic origin story I mean literal jaws if you reach up and you touch your face right now you can feel a jaw in your mouth so this is the one kind of big thing we haven't talked about swimming weird giant bugs and squids we talked about lots of things but what I've not talked about is fish so fish are not super early or late arrivals this is one of my favorite slabs of rock ever this is in the ROM and each one of these things you can see how many there are like 17 31 36 39 40 right this is some kind of mass kill event just like you can find horizons in say the green river formation in the states covered in dead fish and you can buy them at places like the auditorium here in Halifax these are fish but they're really ancient fish so these are from the Burgess Shale remember the Burgess Shale these are Cambrian so let's zoom in and take a look at one of them here's a reconstruction this thing is super primitive but here are it's eyes there is it's notochord which will eventually become a spinal cord and these little gill arches here that's supporting it's gills that's going to help it's breathe and these are the things that are eventually going to be co-opted by evolution remember the Pimp My Ride analogy and they're going to get turned in eventually to jaws to something up over here which includes all the things with jaws how did that happen and when did it happen well we think it happened in the Silurian so I'm first going to tell you what the original the old version of the story was and then I'm going to tell you the new version of the story so first here are some weird guys these are things called astrakoderms here's our astrakoderms and these are jawless fishes they do not have a jaw but they're covered with this super weird armor these look like things somebody made when they were high on drugs these do not look like these look like Pokemon characters or something but these were real organisms swimming around these were the first really successful group of fish but they are jawless importantly so these are the astrakoderms now in a moment we're going to talk about the plakoderms which are a different but related group we'll talk about in one second so there's my astrakoderms but let's get some jaws so here is a diagram of the big groups of fish and I want to point something out I want to point out the overall diversity of fish up here the total number of species of fish is greater today than it was in the past but the total number of separate groups of fish that were around in the Devonian were more so we call this the age of fishes not because they were more actual fish but because the diversity of fish hit this high point in terms of how different there are more total species up here but more bizarrely different things swimming around in the Devonian so the overall story was that we had we thought we had our jawless fish over here and they eventually gave rise to our jawed fish which are including all of our modern things including sharks right here here's our sharks and then all of these other things this is an extinct group called the spiny sharks they went away and these are the things that are still around in the form of lung fishes and seal of cans we'll talk about those later on but these are almost all the fish came off of this group and so their ancestor we think was probably something like a shark so it was probably cartilaginous which by which we mean it did not have bones like a shark does that was the old story and so this thing here represented maybe kind of a primordial ancestor of all of the jawed fish including ourselves because we're of course jawed fish so these are things called and they are Cylurian beasts maybe going back to the Ordovician and we thought they were the oldest representatives of this group the Nathostones which are the jawed fishes nope not anymore not anymore so we got rid of these guys I mean they still exist they're not actually a group by the way they're a paraphyletic group that's something that if you guys have taken biology you will understand the rest of you can just ignore what I just said there they're not a true taxonomic group it's just a morphological one anyways there's our Acanthodians this was the old version of things here's the old version of things so here are the jawless fishes this is the ancestor of all jawless fishes here and so this group here represents ourselves the tetrapods over here but it also represents all the fishes and notice here are the sharks the cartilaginous fishes they are sisters to these guys and so we assume that the ancestor of all these advanced jawed fishes was probably something like a shark and maybe a spiny shark so that was the old hypothesis then and this is the issue with paleontology is that unlike chemistry we can just go to an experiment we often have to just wait and see what fossils come along and then we make hypothesis based on those new fossils 2013 the Chinese described this new beast right here they'd actually had it for a while and didn't think it was anything important until they prepped it and then they noticed something super weird which was this thing is a thing called a placoderm because it has this armored head its head is super armored this is a group here and some of the placoderm had these simple kind of jaws but this thing has a more advanced jaw it's still pretty simple but it has multiple components to it and the important thing was it's super old so this thing then suddenly becomes the ancestor of all the jawed fish now here's where this gets weird before we assume the story went the ancestor of all the jawed fish remember was something like a shark so if the shark you know if the sharks and all the jawed fish all the other jawed fish over here are sister taxa and the sharks don't have any skeletons then you assumed that the ancestor had no skeletons and then later on this group over here evolved you know internal skeletons that's the story on the other hand if we suddenly stick jaws back here with the placoderms the placoderms have a skeleton a partial one on the outside of the body they have that armored head so if we do that then what do we do with these guys who don't have skeletons that means they had to have lost their skeleton at some point which is a pretty radical revision and it's the kind of thing that has to happen when we find new fossils we revise our story so this is the story now that we think happened right so here is this new creature over here here's this new creature and it's got a primitive jaw it's older than the oldest sharks and it's got a bony head on it like this which means that the sharks who lack not only bony heads but bony any things they had to have lost their boniness they had to have lost their boniness the boniness came from here the boniness came from here and everything here kept that boniness but the sharks they lost that boniness along this branch right here we think that is the new version of the story so this it was still a bit controversial in 2013 this is the new version of the story so think back by the way pause for a second if you want here's the placoderms here are the sharks notice that these sharks right including the acanthodians they are sister taxa for us the osteoctesis and this whole group here including including the sharks they are sister taxa to the placoderms and this is the primitive the primitive thing here which is a placoderm like thing this is now the this is this hypothesis okay so that was still a bit controversial but then like any good science if it's true you can keep finding more evidence of it and we did we found two more things that confirm this now they knocked out they knocked out uh in telonathis as the direct ancestor because we found even earlier things that had more advanced features but it represents what one would have looked like and so these are two new ones and we found another one in 2017 so this is the new story so a placoderm like thing was the ancestor of everything sharks and rays and skates and all those guys who have non bony skeletons they lost their boniness right so placoderms didn't have totally bony skeletons but they had some bony heads here and so they had the capacity to at least make bony stuff alright here is our final note on the differences why is it the age of fishes because we have so many weird things swimming around right we have so many weird groups swimming around if you want to look at Devonian organisms including you actually can't find these guys there I don't think but here's an example of a wicked Devonian fish this is Duncleosteus Duncleosteus you might say that's pretty scary looking look at those teeth these are not true teeth these are just extensions of the simple bony jaw these are things in the Silurian and the Devonian this is the scale of them they were massive here's a video I'm not going to show you of this thing swimming around if you want to go see the Devonian the place in the world to see it is in Quebec this is a national park it is also UNESCO World Heritage Site you essentially just keep driving north in New Brunswick until it stops being New Brunswick and there it is so this is UNESCO World Heritage Site it is the place to see Devonian fish these have the greatest collection of Devonian fish in the entire world are found in the rocks around Megasha and we are going to continue that point in the next lecture that's going to be my foreshadowing because the important the most important fossil that occurs here is if not our direct ancestor certainly well on the pathway to being us so the next lecture I'm going to move on land and I'm going to try to start slowly building up things that walk around on land ultimately trying to build us up and the really important component of that story is right up here alright that's where we are please go and complete the online quiz otherwise I will be posting the next lecture on Thursday or Friday