WEBVTT 00:00:00.871 --> 00:00:05.699 >[NICOLE KJERSTEN] So for us to understand the landscape 00:00:05.699 --> 00:00:08.266 of Minnesota as we know it today, 00:00:08.266 --> 00:00:10.982 we need to understand where it came from. 00:00:10.982 --> 00:00:14.383 And to understand that, we have to look back 00:00:14.383 --> 00:00:19.633 to what's happened in this space since the beginning of Earth. 00:00:19.633 --> 00:00:26.132 Earth was formed about 4.6 billion (that's billion with a B) years ago, 00:00:26.132 --> 00:00:29.581 and a lot has happened since then. 00:00:29.581 --> 00:00:36.749 And so we will briefly go over the geological history of Minnesota. 00:00:36.749 --> 00:00:39.749 If you're interested in this topic in depth, 00:00:39.749 --> 00:00:42.932 I would encourage you to take a geology course. 00:00:42.932 --> 00:00:45.049 All we need to know is some context 00:00:45.049 --> 00:00:49.616 for how Minnesota got to be what Minnesota is today 00:00:49.616 --> 00:00:53.632 because we know the landscape is so tightly connected 00:00:53.632 --> 00:00:58.366 to the life that lives in Minnesota. 00:00:58.366 --> 00:01:03.561 Okay, so the Earth, the Earth crust -- 00:01:03.561 --> 00:01:08.482 so that's the outer layer of Earth that's made of rock and dirt and such -- 00:01:08.482 --> 00:01:10.682 it has many, many layers, 00:01:10.682 --> 00:01:14.349 with the oldest layers being at the bottom of the crust 00:01:14.349 --> 00:01:17.273 and the youngest layers being at the top. 00:01:17.273 --> 00:01:20.559 And the observation that Earth has these layers 00:01:20.559 --> 00:01:26.158 and that we find different types of fossils within these layers, 00:01:26.158 --> 00:01:31.225 and that there are different elements within those fossils 00:01:31.225 --> 00:01:35.458 or within those rocks that change over time -- 00:01:35.458 --> 00:01:40.323 the isotopic ratios change over time -- 00:01:40.323 --> 00:01:45.231 from all of that information, we can date the Earth. 00:01:45.231 --> 00:01:47.972 And we've been able to date the Earth 00:01:47.972 --> 00:01:55.018 such that we hypothesize that it was formed about 4.6 billion years ago. 00:01:55.018 --> 00:02:00.184 And by looking at these different layers and dating these different layers, 00:02:00.184 --> 00:02:06.183 we have divided the Earth into four major time periods. 00:02:06.183 --> 00:02:07.400 And what I want to do is, 00:02:07.400 --> 00:02:09.984 I just want to walk through each of those time periods 00:02:09.984 --> 00:02:13.326 and provide a little bit more context for what was happening 00:02:13.326 --> 00:02:19.565 in the landscape that we know of as Minnesota during those different times. 00:02:19.565 --> 00:02:22.733 So we're going to start in the Precambrian era. 00:02:22.733 --> 00:02:29.599 So this is the oldest and longest period of geological time. 00:02:29.599 --> 00:02:35.966 It went from when the Earth was formed 4.6 billion years ago 00:02:35.966 --> 00:02:41.783 to about 600 million (million, with an M) years ago. 00:02:41.783 --> 00:02:45.483 And during this time across the globe 00:02:45.483 --> 00:02:49.115 is when we saw the formation of oceans and continents. 00:02:49.115 --> 00:02:52.416 And I should say, at this point, when we're talking about continents, 00:02:52.416 --> 00:02:55.091 we're talking about one giant conglomeration 00:02:55.091 --> 00:02:57.826 of all the continents that we know today 00:02:57.826 --> 00:03:03.666 that was called Pangea, just one giant landmass. 00:03:05.052 --> 00:03:08.298 During this time, there was lots of volcanic activity, 00:03:08.298 --> 00:03:12.948 so that's putting a lot of different elements into the atmosphere, 00:03:12.948 --> 00:03:17.193 and volcanoes are responsible for forming bedrock 00:03:17.193 --> 00:03:22.365 and the different types of rocks that we see on Earth. 00:03:22.365 --> 00:03:25.381 Not all of them, but a good deal of them. 00:03:25.381 --> 00:03:29.132 And we know that at this point in time, 00:03:29.132 --> 00:03:33.149 Minnesota actually --or what we know of today as Minnesota -- 00:03:33.149 --> 00:03:35.500 was covered by shallow seas. 00:03:35.500 --> 00:03:42.382 So that is the reason we have a lot of iron deposits in northeastern Minnesota 00:03:42.382 --> 00:03:48.415 and why we mine for iron in that area. 00:03:48.415 --> 00:03:53.598 This is a time period when we also start to see the earliest life form, 00:03:53.598 --> 00:03:57.514 even though if we look at this figure here, the fossil record, 00:03:57.514 --> 00:04:04.315 there's not many fossils that were preserved from that time. 00:04:04.315 --> 00:04:10.964 Okay. But there are rocks and there are two types of rock formations 00:04:10.964 --> 00:04:15.514 that I want you to know about that are present here in Minnesota 00:04:15.514 --> 00:04:19.180 that originated during this Precambrian period. 00:04:19.180 --> 00:04:24.557 The first is the Morton Gneiss and then the second is the Canadian Shield. 00:04:24.557 --> 00:04:27.194 Let's talk about the Morton Gneiss first. 00:04:27.194 --> 00:04:30.378 This is the oldest type of rock that is found in Minnesota 00:04:30.378 --> 00:04:34.628 and it is located along the Minnesota River Valley 00:04:34.628 --> 00:04:38.162 kind of near Granite Falls, if you know where that is. 00:04:38.162 --> 00:04:40.343 So here's a map of Minnesota, 00:04:40.343 --> 00:04:43.695 and this orange rusty color 00:04:43.695 --> 00:04:49.864 is shading in the areas where you can find Morton Gneiss type of rock. 00:04:49.864 --> 00:04:53.118 [pronounced] "Neese"? "Ness"? I think I'm pronouncing that correctly. 00:04:53.118 --> 00:04:56.259 (One of those ways is correct, at least.) 00:04:56.259 --> 00:05:00.900 The second type of rock is the Canadian Shield, 00:05:00.900 --> 00:05:03.800 and this is really just a massive layer of rock 00:05:03.800 --> 00:05:10.365 that is present not only in Minnesota, but also a good portion of Canada. 00:05:10.365 --> 00:05:15.132 And so here's a map of the northern portion of North America, 00:05:15.132 --> 00:05:18.582 and all of this area shaded in purple 00:05:18.582 --> 00:05:24.215 represents the rock that makes up the Canadian Shield. 00:05:24.215 --> 00:05:30.369 And if you've gone into central northern Minnesota or northeastern Minnesota, 00:05:30.369 --> 00:05:32.936 you can see this exposed rock 00:05:32.936 --> 00:05:37.185 in various areas such as the Boundary Waters Canoe Area. 00:05:37.185 --> 00:05:45.469 These exposed rocks are actually have been around for millions to billions of years. 00:05:45.469 --> 00:05:51.718 And you can also see it along these cliffs in the North Shore. 00:05:51.718 --> 00:05:54.668 Okay, so back to our timeline, 00:05:54.668 --> 00:05:58.251 we're now going to move to the Paleozoic era. 00:05:58.251 --> 00:06:04.936 And this was a time period 600 to 225 million years ago. 00:06:04.936 --> 00:06:08.552 And believe it or not, at this point in time, 00:06:08.552 --> 00:06:13.636 Minnesota is actually thought to be located near the equator. 00:06:13.636 --> 00:06:18.671 So remember, when all the continents are mushed together in Pangea 00:06:18.671 --> 00:06:26.176 before plate tectonic separated them into the locations that they are today, 00:06:26.176 --> 00:06:28.537 not everything is in the place that it is today 00:06:28.537 --> 00:06:31.669 [corrects self] Not everything was in the place that it is today. 00:06:31.669 --> 00:06:35.150 And so Minnesota is actually located near the equator, 00:06:35.150 --> 00:06:43.781 which means that there was a lot warmer temperatures, maybe more moisture. 00:06:43.781 --> 00:06:48.028 And that is one of the reasons why in the fossil record, 00:06:48.028 --> 00:06:51.962 we see evidence of tropical and subtropical plants. 00:06:51.962 --> 00:06:56.186 It's also important to note that there were continental seas 00:06:56.186 --> 00:06:58.521 that were present in Minnesota at this time, 00:06:58.521 --> 00:07:00.737 which is why in the fossil record, 00:07:00.737 --> 00:07:05.915 we can see evidence of marine organisms being present in Minnesota, 00:07:05.915 --> 00:07:09.496 despite the fact that we don't have an ocean today. 00:07:09.496 --> 00:07:13.143 Okay, so the next time period is the Mesozoic period. 00:07:13.143 --> 00:07:18.808 This was between 225 and 65 million years ago. 00:07:18.808 --> 00:07:21.311 Again, we're still under water. 00:07:21.311 --> 00:07:26.888 There's still continental seas covering at least portions of the state. 00:07:26.888 --> 00:07:29.937 It's also when we see the first flowering plants, 00:07:29.937 --> 00:07:32.004 the first birds, the first mammals, 00:07:32.004 --> 00:07:37.787 even though this is sometimes referred to as the period as the age of the dinosaurs. 00:07:37.787 --> 00:07:42.148 So dinosaurs tend to be more prevalent than mammals at this point. 00:07:44.447 --> 00:07:46.980 And it's also what's happening 00:07:46.980 --> 00:07:49.513 with where Minnesota is located on the globe is, 00:07:49.513 --> 00:07:52.968 it is starting to get pulled more northwards, 00:07:52.968 --> 00:07:56.245 and so it's getting pulled towards the poles, 00:07:56.245 --> 00:08:01.738 and it's starting to experience a cooler and somewhat drier climate 00:08:01.738 --> 00:08:05.108 than what it did when it was near the equator. 00:08:05.108 --> 00:08:08.611 And here's just an example of some of the fossils that have been found 00:08:08.611 --> 00:08:11.093 in Minnesota during this time period 00:08:11.093 --> 00:08:15.828 such as small, small vertebrate animals and flowering plants 00:08:15.828 --> 00:08:20.694 that have been preserved in the different layers of rocks 00:08:20.694 --> 00:08:24.544 that have been dated to the Mesozoic. 00:08:24.544 --> 00:08:27.895 Okay, and then our final time period is the Cenozoic. 00:08:27.895 --> 00:08:32.157 That is from 65 million years ago to present. 00:08:32.157 --> 00:08:35.278 And this is known as the age of mammals, 00:08:35.278 --> 00:08:42.307 where we see the dinosaurs have died out and the mammals are starting to rule. 00:08:42.307 --> 00:08:46.398 It's also a period where there's intense glaciation, 00:08:46.398 --> 00:08:53.945 and so Minnesota has made it to where it presently is located on the globe. 00:08:53.945 --> 00:08:59.577 And not only did Minnesota see a cooling period, 00:08:59.577 --> 00:09:03.327 but there was just a large cooling period across the globe, 00:09:03.327 --> 00:09:06.246 which resulted in glacier formations. 00:09:06.246 --> 00:09:12.088 And glaciers had a huge impact on the present landscape, 00:09:12.088 --> 00:09:15.321 which we'll learn more about in the next lecture. 00:09:15.321 --> 00:09:23.322 Which we will get to after I wrap this up and say thank you for your attention. 00:09:23.322 --> 00:09:28.654 And like I've already previewed, we will talk about glaciers next.