CH 1.2: MN Geological History https://youtu.be/T5pfp8z2Cqw >[NICOLE KJERSTEN] So for us to understand the landscape
of Minnesota as we know it today,
we need to understand where it came from.
And to understand that, we have to look back
to what's happened in this space since the beginning of Earth.
Earth was formed about 4.6 billion (that's billion with a B) years ago,
and a lot has happened since then.
And so we will briefly go over the geological history of Minnesota.
If you're interested in this topic in depth,
I would encourage you to take a geology course.
All we need to know is some context
for how Minnesota got to be what Minnesota is today
because we know the landscape is so tightly connected
to the life that lives in Minnesota.
Okay, so the Earth, the Earth crust,
so that's the outer layer of Earth that's made of rock and dirt and such.
It has many, many layers,
with the oldest layers being at the bottom of the crust
and the youngest layers being at the top.
And the observation that Earth has these layers
and that we find different types of fossils within these layers,
and that there are different elements within those fossils
or within those rocks that change over time.
The isotopic ratios change over time.
From all of that information, we can date the Earth.
And we've been able to date the Earth
such that we hypothesize that it was formed about 4.6 billion years ago.
And by looking at these different layers and dating these different layers,
we have divided the Earth into four major time periods.
And what I want to do is,
I just want to walk through each of those time periods
and provide a little bit more context for what was happening
in the landscape that we know of as Minnesota during those different times.
So we're going to start in the Precambrian era.
So this is the oldest and longest period of geological time.
It went from when the Earth was formed 4.6 billion years ago
to about 600 million (million, with an M) years ago.
And during this time across the globe
is when we saw the formation of oceans and continents.
And I should say, at this point, when we're talking about continents,
we're talking about one giant conglomeration of all the continents that we know today
that was called Pangea, just one giant landmass.
During this time, there was lots of volcanic activity,
so that's putting a lot of different elements into the atmosphere,
and volcanoes are responsible for forming bedrock
and the different types of rocks that we see on Earth.
Not all of them, but a good deal of them.
And we know that at this point in time,
Minnesota actually --or what we know of today as Minnesota --
was covered by shallow seas.
So that is the reason we have a lot of iron deposits in northeastern Minnesota
and why we mine for iron in that area.
This is a time period when we also start to see the earliest life form,
even though if we look at this figure here, the fossil record, there's not many fossils that were preserved from that time.
Okay. But there are rocks and there are two types of rock formations
that I want you to know about that are present here in Minnesota
that originated during this Precambrian period.
The first is the Morten gneiss and then the second is the Canadian shield.
Let's talk about the Morton Gneiss first.
This is the oldest type of rock that is found in Minnesota
and it is located along the Minnesota River Valley
kind of near Granite Falls, if you know where that is.
So here's a map of Minnesota,
and this orange rusty color
is shading in the areas where you can find Morton Gneiss type of rock.
Nes Nest I think I'm pronouncing that correctly.
One of those ways is correct, at least.
The second type of rock is the Canadian Shield.
And this is really just a massive layer of rock
that is present not only in Minnesota, but also a good portion of Canada.
And so here's a map of the northern portion of North America,
and all of this area shaded in purple
represents the rock that makes up the Canadian Shield.
And if you've gone into central northern Minnesota or northeastern Minnesota,
you can see this exposed rock in various areas such as the Boundary Waters Canoe Area.
These exposed rocks are actually have been around for millions to billions of years.
And you can also see it along these cliffs in the North Shore.
Okay, so back to our timeline, we're now going to move to the Paleozoic era.
And this was a time period 600-225 million years ago.
And believe it or not, at this point in time,
Minnesota is actually thought to be located near the equator.
So remember, when all the continents are mushed together in Pangea
before plate tectonic separated them into the locations that they are today,
um, No everything is in the place that it is today.
Not everything was in the place that it is today.
And so Minnesota is actually located near the equator,
which means that there was a lot warmer temperatures, maybe more moisture.
And that is one of the reasons why in the fossil record,
we see evidence of tropical and subtropical plants.
It's also important to note that there were continental seas
that were present in Minnesota at this time, which is why in the fossil record,
we can see evidence of marine organisms being present in Minnesota,
despite the fact that we don't have an ocean today.
Okay, so the next time period is the Mesozoic period.
This was 225 to 265 million years ago.
Again, we're still underwater.
There's still continental seas covering at least portions of the state.
It's also when we see the first flowering plants, the first birds, the first mammals,
even though this is sometimes referred to as the period as the age of the dinosaurs.
So dinosaurs tend to be more prevalent than mammals at this point.
And it's also what's happening with where Minnesota is located on the globe is,
it is starting to get pulled more northwards,
and so it's getting pulled towards the poles,
and it's starting to experience a cooler and somewhat drier climate
than what it did when it was near the equator.
And here's just an example of some of the fossils that have been found
in Minnesota during this time period
such as small, small vertebrate animals and flowering plants
that have been preserved in the different layers of rocks
that have been dated to the Mesozoic.
Okay, and then our final time period is the Cenozoic.
That is from 65 million years ago to present.
And this is known as the age of mammals,
where we see the dinosaurs have died out and the mammals are starting to rule.
It's also a period where there's intense glaciation,
and so Minnesota has made it to where it presently is located on the globe.
And not only did Minnesota see a cooling period,
but there is just a large cooling period across the globe,
which resulted in glacier formations.
And glaciers had a huge impact on the present landscape,
which we'll learn more about in the next lecture.
Which we will get to after I wrap this up and say thank you for your attention.
And like I've already previewed, we will talk about glaciers next.