WEBVTT

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CH 1.2: MN Geological History
https://youtu.be/T5pfp8z2Cqw
>[NICOLE KJERSTEN] So for us 
to understand the landscape 

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of Minnesota as we know it today, 

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we need to understand where it came from.

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And to understand that, 
we have to look back 

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to what's happened in this space 
since the beginning of Earth.

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Earth was formed about 4.6 billion
(that's billion with a B) years ago, 

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and a lot has happened since then.

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And so we will briefly go over 
the geological history of Minnesota.

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If you're interested in this topic in depth, 

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I would encourage you 
to take a geology course.

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All we need to know is some context 

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for how Minnesota got to be 
what Minnesota is today 

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because we know the landscape 
is so tightly connected 

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to the life that lives in Minnesota.

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Okay, so the Earth, the Earth crust, 

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so that's the outer layer of Earth 
that's made of rock and dirt and such.

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It has many, many layers, 

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with the oldest layers being 
at the bottom of the crust 

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and the youngest layers being at the top.

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And the observation 
that Earth has these layers 

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and that we find different types 
of fossils within these layers, 

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and that there are different 
elements within those fossils 

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or within those rocks 
that change over time.

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The isotopic ratios change over time.

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From all of that information, 
we can date the Earth.

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And we've been able to date the Earth

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such that we hypothesize that it was 
formed about 4.6 billion years ago.

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And by looking at these different layers 
and dating these different layers, 

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we have divided the Earth 
into four major time periods.

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And what I want to do is, 

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I just want to walk through 
each of those time periods 

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and provide a little bit more context 
for what was happening 

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in the landscape that we know of as Minnesota during those different times.

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So we're going to start
in the Precambrian era.

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So this is the oldest and longest
period of geological time.

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It went from when the Earth 
was formed 4.6 billion years ago 

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to about 600 million 
(million, with an M) years ago.

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And during this time across the globe 

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is when we saw the formation 
of oceans and continents.

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And I should say, at this point, 
when we're talking about continents, 

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we're talking about one giant conglomeration
of all the continents that we know today 

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that was called Pangea, 
just one giant landmass.

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During this time, there was 
lots of volcanic activity, 

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so that's putting a lot of different elements into the atmosphere,

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and volcanoes are responsible 
for forming bedrock 

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and the different types 
of rocks that we see on Earth.

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Not all of them, but a good deal of them.

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And we know that at this point in time, 

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Minnesota actually --or what 
we know of today as Minnesota  --

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was covered by shallow seas.

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So that is the reason we have a lot of 
iron deposits in northeastern Minnesota 

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and why we mine for iron in that area.

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This is a time period when we also 
start to see the earliest life form, 

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even though if we look at 
this figure here, the fossil record, 
there's not many fossils 
that were preserved from that time.

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Okay. But there are rocks and there 
are two types of rock formations 

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that I want you to know about
that are present here in Minnesota 

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that originated during this Precambrian period.

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The first is the Morten gneiss and then the second is the Canadian shield.

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Let's talk about the Morton Gneiss first.

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This is the oldest type of rock 
that is found in Minnesota 

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and it is located along 
the Minnesota River Valley 

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kind of near Granite Falls, 
if you know where that is.

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So here's a map of Minnesota, 

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and this orange rusty color 

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is shading in the areas where you 
can find Morton Gneiss type of rock.

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Nes Nest I think I'm pronouncing that correctly.

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One of those ways is correct, at least.

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The second type of rock is the Canadian Shield.

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And this is really just a massive layer of rock 

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that is present not only in Minnesota, 
but also a good portion of Canada.

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And so here's a map of the northern portion of North America, 

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and all of this area shaded in purple 

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represents the rock that makes up 
the Canadian Shield.

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And if you've gone into central northern 
Minnesota or northeastern Minnesota, 

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you can see this exposed rock in various areas 
such as the Boundary Waters Canoe Area.

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These exposed rocks are actually have been
around for millions to billions of years.

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And you can also see it along 
these cliffs in the North Shore.

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Okay, so back to our timeline, 
we're now going to move to the Paleozoic era.

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And this was a time period 
600-225 million years ago.

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And believe it or not, 
at this point in time, 

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Minnesota is actually thought 
to be located near the equator.

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So remember, when all the continents are mushed together in Pangea 

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before plate tectonic separated them 
into the locations that they are today, 

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um, No everything is in the place that it is today.

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Not everything was in the place that it is today.

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And so Minnesota is actually 
located near the equator, 

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which means that there was a lot warmer temperatures, maybe more moisture.

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And that is one of the reasons 
why in the fossil record, 

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we see evidence of tropical 
and subtropical plants.

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It's also important to note 
that there were continental seas 

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that were present in Minnesota at this time, 
which is why in the fossil record, 

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we can see evidence of marine organisms being present in Minnesota, 

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despite the fact that we 
don't have an ocean today.

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Okay, so the next time period 
is the Mesozoic period.

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This was 225 to 265 million years ago.

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Again, we're still underwater.

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There's still continental seas 
covering at least portions of the state.

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It's also when we see the first flowering plants, the first birds, the first mammals, 

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even though this is sometimes referred to
as the period as the age of the dinosaurs.

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So dinosaurs tend to be more 
prevalent than mammals at this point.

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And it's also what's happening with where Minnesota is located on the globe is, 

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it is starting to get pulled
more northwards, 

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and so it's getting pulled towards the poles, 

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and it's starting to experience 
a cooler and somewhat drier climate 

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than what it did when it was near the equator.

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And here's just an example of some 
of the fossils that have been found 

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in Minnesota during this time period 

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such as small, small vertebrate 
animals and flowering plants 

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that have been preserved 
in the different layers of rocks 

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that have been dated to the Mesozoic.

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Okay, and then our final 
time period is the Cenozoic.

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That is from 65 million years ago to present.

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And this is known as the age of mammals, 

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where we see the dinosaurs have died out 
and the mammals are starting to rule.

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It's also a period where 
there's intense glaciation, 

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and so Minnesota has made it to where 
it presently is located on the globe.

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And not only did Minnesota 
see a cooling period, 

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but there is just a large 
cooling period across the globe, 

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which resulted in glacier formations.

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And glaciers had a huge impact 
on the present landscape, 

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which we'll learn more about in the next lecture.

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Which we will get to after I wrap this up 
and say thank you for your attention.

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And like I've already previewed, 
we will talk about glaciers next.