Hey everybody, welcome back! We're getting
right back into our environmental
science studies today with a look at the
planet: planet Earth. The reason why we
have to look at Earth and what it does
and how it behaves is because it's the
environmental canvas. Everything else is
reacting to what the earth is. And so we
need to talk about it a little bit. Now
we actually have a very long series
already on this channel on earth and space science
X, you can click there and then you can
see an entire series that deals with
many of the things that we're gonna just
hit on just very quickly in this lecture.
But if you're just interested the
environmental studies aspect of this
particular topic than you can stay right
here and we'll cover most of those
things...the highlights...really quickly. So
geology is the basis for environmental
science. The reason why is because
everything on the environment, everything
in the environment, is responding to
physical processes that are either above,
at, or below the earth's surface.
These processes, they control the shape
of the landscape, they lay the foundation
for the environmental systems in life,
they provide raw materials for
industries such as iron, copper, and steel.
They provide energy from fossil fuels
and geothermal sources. All of this is in
the processes that the earth is wrapped
up in, between the earth and actually the
Sun, of course. As we discussed in our
last lecture, ultimately fossil fuels are
trapped sunlight. Right. Those are old
living organisms that went through
photosynthesis and that energy is then
trapped into the petroleum reserves on
earth. And the way that we go about
studying the earth is through a science
called geology. Geology is the study of
Earth's physical features, processes, and
life...I'm sorry...and history. A human
lifetime is just a blink of eye in
geologic time. The earth is really old.
It's about four-and-a-half billion years
old and a lot can happen in four and a
half billion years. In fact, on earth
a lot has happened. So here we see the
earth as it exists today. This is a
photograph that was taken, or that I
actually collected from Wikipedia on May
30th 2020, so this is a fairly recent
image. But if we were to look at pictures
of the earth from say 60 million years
ago, a 100 million years,
a billion years ago, it would look very
different than what we're seeing on this
image. We even get into that here in a
moment. Now the way that the earth is set
up right now is that it has a series of
layers in it. When the earth was
originally formed a lot of people
believe it was all homogenous, it's all
mixed up but since then it's settled out,
almost like the way that oil and vinegar
settle out in salad dressing. So the
earth is consisted of layers. There's
something called the core at the very
center. This is very dense. It's made out
of nickel and iron material...it's
believed to be an alloy of these things.
And there's two phases of the core.
There's the very center of the earth
where the inner core is and it's a solid
sphere. It's a sphere of solid nickel and
iron. Around that is the outer core the
outer core is molten, it's a shell around
the inner core that is in constant flow
within the earth. So it is swirling
around. And when we look at this diagram
over here...here we see the solid sphere
in the middle, this is the inner core
outside around it, this is the outer core...
it's liquid iron and nickel swirling
around. And some people actually believe
it's moving around at a pretty quick
velocity. Around this liquid outer core
that we see here...also in this image
here...is the mantle. The mantle is less
dense, it doesn't...gravity doesn't pull it
down as effectively so it sits a little
bit higher. It's still pretty dense
compared to the rocks we have up here on
the surface but they're less dense than
the core. They're less dense, its elastic
rock composed of mainly silicon and
aluminum oxide minerals. Some of the
minerals will be familiar to you.
Things, well...mainly minerals like,
especially in the upper part of it,
feldspar. Represents most of Earth's
volume and it contains most of the
radioactive elements that keeps Earth's
interior very hot especially thorium,
there's uranium in there, but thorium is
another big one. And also included in
this is something called the
asthenosphere. Now the asthenosphere is
very soft or melted rock located just
below the lithosphere...which we haven't
talked about [but will] here in a minute.
So the mantle is this big large
section right here, right. So here's the
mantle right up to the top of something
called the crust, and the crust actually
has this red layer right in here, the
asthenosphere, and it's pretty soft. Now
the material above it is actually rigid
and hard. The material down below it is
actually relatively rigid, I mean its
elastic. But it's this is actually very,
very soft and in some cases almost to
the point of actually melting. It's very
very close to that point. So this is soft
and this is rigid up here on top. And the
the mantle itself is the source of most
geothermal energy on earth. Iron and nickel
is not radioactive,
so most of the radioactive elements are
not believed to be radiating their heat
from here. We believe that most of it's
actually coming from the mantle and
that's where the heat budget for the
earth is coming from. Get into that here
in a short period of time. So
think about this. We've got solid, a very
solid iron-nickel core, and liquid,
convecting...we're gonna get into what convection
is a little bit later on...but convecting
iron-nickel outer core. A rigid mantle
but right at the edge of that mantle,
right at the edge there, there's this
thing called the asthenosphere and
sitting on top of the asthenosphere is
the lithosphere. Lithosphere is something
a little bit different. So the crust is
the thin brittle low-density layer of
rock sitting on the top. That's where we
are right now sitting on top of the
crust. And the crust is also part of the
lithosphere.
It's the uppermost mantle and the crust.
So here's the mantle all the way up to
that black line where the earth where
the lithosphere starts. We got crust up...
I'm sorry...we got mantle up here. And
so we've got asthenosphere and then
upper mantle right here. That means that
the upper part of the mantle is soft and
gooey. There's a good way of thinking of
it, whereas down below it is a little bit
more rigid. And then there's a crunchy
top up here on the top. That's the
crust and the lithosphere up at the top.
Alright.
That's important because when we look at
the earth we've discovered some really
fascinating things. Since especially the
1960s. And one of the
main things that we've discovered is the
concept of plate tectonics. Plate
tectonics is the...is the recognition that
the earth's lithosphere...it's that crunchy part up on the surface,
the very top of the earth...is fractured
and composed of numerous continually
moving plates. Currently there are seven
major plates. Right. You can see them. You
know here's the Pacific plate, the North
American plate, the Eurasian Plate, Africa...
the African plate, South American plate,
and the Antarctic plate. And several
dozen microplates...you know, the Juan de
Fuca is one of these and you can find
them actually here, small versions of
them on the, on this diagram represented...
have been identified on earth. So the
earth is just fractured up. And so if we
just think of the main seven major
plates moving around over time, you
realize that things are gonna get pretty
interesting. And we've noticed that
there's some interesting associations.
Like there's a close association between
plate edges...so here's a plate right here,
this is the Pacific plate...and volcanoes.
Sure enough, here's the edge of the plate
and those little purple triangles that
we see in here are volcanoes. These are
actually volcanoes that exist at the
surface, these are not the undersea
volcanoes. These are the ones that we
just see up here at the surface. We also
get our earthquakes at those locations.
These are where the epicenters of many
earthquakes occur, is right on that
edge, and other violent events on earth.
Tsunamis for example. An example of this
is right here, here's Japan. Japan was hit
by a tsunami roughly 10 years ago and the
effect has been the shutdown at the
Fukushima nuclear power plant which
actually went into meltdown. Right along Japan here, right from
southern...or I'm sorry eastern...Russia on
the Kamchatka Peninsula, we see a series
of volcanoes. There's...in addition to
volcanoes, there's earthquake epicenters
here, very large ones all the time. And
then we get the tsunamis as well. So that
association, it turns out, is not
accidental. And we're going to get into
that here in a moment when we go
step-by-step through what these edges
are. But notice out here it's kind of
boring.
I mean, Hawaii is out here but Hawaii, it
turns out, is an aberration. It's
an anomaly. Most of the time volcanoes
occur right along the plate boundaries.
Alright. So the question of how in the
world does the lithosphere...those plates...
how do those move around on the surface,
how do...what actually motivates that to
occur? And the current thinking is this
concept of mantle convection. In other
words, it's the lithosphere that's
floating on top of something that's
happening down even deeper in the earth.
So the mantle convection concept is the
very slow creeping motion of Earth's
solid, silicate mantle. So silicates...those
include your feldspars that I had mentioned
earlier, those are the minerals that we
find in those rocks down in the mantle...
silicate mantle caused by convection
currents carrying heat from the interior
to the planet's surface. Okay. So there's
a couple of sources of heat down in the
earth. There's radioactive heat from
the mantle, and that's estimated at
between 15 and 41 terawatts, and
primordial heat which is between 12 and
30 terawatts, which drive the convection
current. So the earth has radioactivity
within it that's always driving that...
drives a need for the heat to escape.
It's just a thermodynamic process. We
actually talked about that a little bit
when we talked about entropy. So we have heat
here in the mantle and it wants to
escape out to the cooler portions of the
surface of the earth. Alright. So this
radioactive heat is one source.
Primordial heat: basically when the earth
was formed...you have these large objects
slamming into each other as the earth
accumulated all this material...and when
you take two very large objects and
drive them together you can actually
produce a lot of heat energy in that way.
You're basically converting energy from
the motion of the object into heat
energy through the collision. Okay. So
things get really hot it turns out when
you do this. What happens is it pushes
the mantle's soft rock up. So the mantle or
as we talked about is...it can be...
especially gooey up here at the top, but
over very long periods of time the
elastic mantle
is actually able to circulate in a
convection cell. So here's the outer core,
here's the lithosphere up here at the
top. And so it's pushing right here. Here
we see that push right there. Like a
conveyor belt. And, let's see here...pushes
the mantle soft rock up as it warms and
down as it cools like a conveyor belt. So
here we see it moving down. The
lithosphere is dragged along with the
mantle, okay. So as the mantle moves the
lithosphere is experiencing force. In
this case there's a force that's trying
to pull the lithosphere in this
direction on the other side is trying to
pull it in this direction. Okay. That's
the concept that we see here. Now over
here on the side, we see that this one
and this one are coming together. So
there's actually a force pushing this
one and this one together. Okay. The idea
of how convection works...a good example
that you might see in life is just when
you boil water in a pot, so that's what
we have up over here...is we got this
boiling pot up here on the top, the water
down at the bottom gets really hot. It
circulates up to the top, releases its heat,
drops back down
and it just keeps circulating around. And
when you do that you get things moving
around at the surface. That brings about
a concept called Pangaea which means "all
land" and Panthalassa.
Panthalassa is the concept of all one
world ocean. So Pangaea is all land
masses being joined together to a
supercontinent 225 million years ago. So
the continents...we do believe...have
combined, separated, and recombined over
millions of years...even billions of years...
and this is just an example of what we
think has happened just over the last
say 200 million years. Now the earth,
again is 4.5 or 4.6 billion years old,
when we round round it up, 4.6 billion
years old, so this process of continents
being large and breaking up and then reaccumulating into other large continents
again has probably happened over and
over and over again.
Okay, so this is what we believe the
earth looked like about 225...I'm sorry 200
million years ago...and this is how it
would have broken up into its current
orientation today. Alright, so what we
need to do now is explore the way that
these plates can move around on the
surface of the earth and how they tend
to interact. It turns out there's three
different ways they can do it. One way is
they can diverge. In other words the
plates have the ability to move away
from each other. That's what we've demonstrated on
the previous slide. So it turns out
there's some pretty interesting things
that tend to happen at divergent plate
boundaries. One of the most famous plate
boundaries...divergent plate boundaries...
goes right through the middle of the
Atlantic Ocean. And this is the divergent
plate boundary that separated South
America and Africa from each other about
200 million years ago. So when this
happens, plates are moving apart and
forming large rift valleys. These rift
valleys can be quite deep. They could be
quite magnificent. But most of the time
they're at the bottom of the ocean.
Sometimes we get lucky and they actually
wind up at the surface. There's a Rift
Valley...if we look here at this mid-ocean rift right here...this is Iceland.
Located, oh, I'm sorry...Iceland is right up here...I had it
at the wrong location.
So here's Iceland. And so you can see
that rift is going to go right through
the middle of the island, and sure enough
that's what we're seeing here. These are
divers in the mid-Atlantic rift zone...in
going through Iceland. So the rift right
here is in shallow water and so you're
able to come in here, on one side is the
North American plate on the other side
is the Eurasian plate. And basically the
earth is splitting right here. It's
amazing. So what happens to these
locations? Well, magma rises into the
rifts. So magma is molten rock. We're
gonna talk a little bit more about what
magma is when we get to volcanoes a
little bit later on, but it's molten rock
that rises into the rifts, to the surface
and creates new crust when it solidifies.
Basically, when you have magma that rises
up and fills into this gap it interacts
with the seawater. The sea water
immediately quenches it and cools it
into rock right away. Because these rifts
are made of young hot rock...in other word
this whole thing can still be hot even
though it's in cold water that'll be a
lot hotter than the rocks around it
because it's right next to it large, what
we call the magma chamber, they sit high
on the Earth's surface forming long
chains of undersea mountains with a
central Rift Valley. This is simply
because when things are hotter they are
less dense, and things that are less
dense they sit higher. So when we look
back on this picture of the earth again,
this mid-.... the I'm sorry the mid-Atlantic
Rift Valley that's right here in the
middle, the big rift zone...it also happens
to sit right on the top of a large
mountain chain, the largest mountain
chain on planet earth. Okay. And it just
turns out that Iceland is sitting right
on top of it. And underwater volcanoes
and hydrothermal vents are very common.
In terms of earthquakes, there are little
earthquakes that happen out here but
they don't tend to be very, very large.
But there are a lot of volcanoes here.
The vast majority, in fact, of volcanoes
occur at these mid-ocean rift
zones. Alright. Another way that plant...
I'm sorry...that plates can interact with
one another is through collisions. Alright. So instead of moving away...if
they're moving away here then they have
to be running into each other
somewhere else....and it does turn out that
there are three different ways that they
can collide. And this is based on the
fact that there are three different
kinds of lithosphere...I'm sorry...crust
that can run into each other. The three
kinds of convergent boundaries are: ocean
to continent; in other words the oceans,
which are made of a different kind of
crust than the continents are, it tends
to be denser, and it's it's lower. When
you run an ocean into the continent
something very interesting happens. You
can take an ocean you can run it into
another ocean crust. When that happens
something interesting happens and we'll
talk about the rules for that here in a
moment. And then there's when continents
run into other continents. In order to
understand what's going to happen here
we have to understand this concept of
subduction. So subduction is a process in
which the ocean, oceanic plate slides
beneath less than
crust. In other words, when you have two
things running into each other
something's got to make space for the
other thing. And there's only two ways to
go; you can go over or you can go under,
right. So subduction is when it goes
under. And remember, if the oceanic crust
is denser it can actually just drive
itself right underneath the other plate.
So ocean crust, it turns out as a rule, is
always subducted beneath continental
crust with rare exceptions. Right. There's
something called abduction: this is where
occasionally the oceanic crust is
scraped off and moved on to this edge of
the continent, but for the most part
continental crust, which is ten percent
less dense than oceanic crust will tend
to not subduct whereas the oceanic crust
will almost always go under. Now what
about if we have two bits of oceanic
crust?
Well, older-colder, that's right. If we go
back to this old image over here, the red
zone is the young, hot rock here. This where
all the volcanoes are. As it spreads away
from here the rocks get younger [note: meant to say "older"], they get
colder and they sit lower because they
become more dense. So older, colder
oceanic crust always subject, subjects...
this should say "subducts"...beneath
younger, hotter ocean crust. So sorry
about this, this is a typo in the
slide. And continental crust does not
subduct.
When two continents collide...under
scenario number three...when two
continents collide that's a
clear-cut case for something different
is going to happen. We're going to get
into at a moment. Alright.
So when oceans to ocean...er I'm sorry...
when ocean to continent convergence
occurs, there's a couple things that
happen. First the oceanic crust subducts
beneath the continental crust. So here we
have the lithosphere, here's that
asthenosphere, remember the asthenosphere
is slick. It allows things to move and
slide up on top of it. The lithosphere
sitting on top of it, is going to move
and subduct beneath the continental crust
that we see over here.
Continental crust is thicker, it's less dense,
it's just not gonna go under.
It's sitting at the Earth's surface
for a reason. And what happens is the
oceanic crust will get recycled back
into the mantle. So this will come down,
it'll arch and bend its way down into
the earth, and basically be recycled into
the earth. Right alongside that it will
typically form a long, deep trench where
the seafloor bends and slides beneath
the continent. That trench...in this
image...is right here. So that trench
occurs right where the lithosphere bends,
the oceanic lithosphere will bend, and go
right down into the earth. And it may
have something called an accretionary
prism. Not always, but it might have it.
An accretionary prism is when you have
a bunch of oceanic sediment...
I don't know, sand, clay, silt, material
washed from rivers out into the trench...
it might get scraped up and accumulated
in the trench. That's what we mean by an
accretionary prism. Not all the time does
it exist but sometimes it's there. Okay. I
would say most of the time there's a
little bit at least but there are
moments where it's not. There tends to
also be explosive volcanoes, like Mount
St. Helens. Here, we see what happens here
is the lithosphere, the oceanic
lithosphere, will...er...the oceanic crust
will then be subducted under the
lithosphere and the oceanic crust
there's a lot of water in it. And it
turns out that water, when it's mixed
with rock a very high heat will lower
the melting point of rock, and so rocks
down here that...you can see the rocks
right here, right where I have the cursor...
don't melt, but the ones over here do. And
that's because there's water mixed into
it. So when you lower the melting point
of rocks they'll tend to flash into
magma and that magma will rise,
right. Liquids tend to rise because
they're less solid on average. So that
magma will rise and it'll form a volcano.
This is really just the way of the water
trying to get its way back into the, up
to the Earth's surface. And because
there's water they tend to be explosive.
Right. Steam explosions tend to happen.
Massive earthquakes and tsunamis are
also very common. I mean, you can imagine
if you're gonna take the entire part of
the crust and shove it underneath an
entire other part of the crust, you're
gonna get massive earthquakes and, in
fact, these can be
quite large. Magnitude nine or larger
sometimes. Another way that we can move
them together is instead of taking the
continent and the ocean we can actually
take two bits of the ocean and converge
them. So we get ocean to ocean
convergence. And this is actually pretty
common too it turns out we just don't
always interact with it as much as we're
accustomed to because we don't live in
the oceans on average as much as we live
on the continents. But it does happen.
What we tend to see is that older,
oceanic crust subducts beneath younger,
hotter oceanic crust. I always say old
and cold goes...subducts beneath young and
hot. That's just how it is. What we see
here is a subduction zone. This right
here...little pluses here...are the zones of
earthquakes so we could actually see
where earthquakes are generated as this
plate is subducted and recycled back
beneath the asthenosphere. And what it'll
do is it'll form in typically three
different lines that we see at the
surface of the earth. So you might get an
accretionary prism, remember that's that
stuff scraped off as it's going down and
it builds a big pile up, up at the top. So
those are the scrapings as this plates
subducts down underneath this other one
over here. It'll also form a volcanic
line, something we call a volcanic arc. So
you'll get the accretionary prism here
you'll get the volcanic line here and
this is where you get that volcanism.
Just like we saw over here, same thing is
happening but it's happening here. It's a
different chemistry for the most part,
and you get it in different locations
but you can get pretty amazing volcanic
systems
when this occurs. These systems typically
also are associated with long, deep
trenches where the seafloor bends and
slides beneath something called the
volcanic arc. We talked about that
right here. These are amongst the largest
features on earth. Let me give you an
example of where this happens. This is
Guam.  Guam is 1332 feet above sea level, it's
located right here. So this little island...
there's a major US military base located
there. And you can see right next
to it, here's the Marianas Trench. And
right next to it is challenger deep,
which is located about right here. This
is an approximation. Challenger deep is
35,827 feet
deep. This is deeper
than Mount Everest is tall. So Mount
Everest, if memory serves is 29,029 feet...
you might want to check me on that but I
think that's the right height...
that's enough distance for you to put
the entire, the top of the Himalayan
mountains with Mount Everest into the
bottom of the challenger deep and
there'd still be over a mile of water
just to get to the beach. And then to get
to the top of Guam is 1332 feet. So if we
start here and we start working up this
embankment all the way till we hit the
top of Guam, the highest elevation at the
volcano located right over here, we're
talking about almost 30...
I guess 3700...over 37,000 feet of
elevation change. I mean that's where
jetliners...I mean they fly even
sometimes not even that high...so we're
talking about very, very, very, deep all
the way to extremely high, in terms
of this feature. If the ocean wasn't there
you'd see it, it would be one of the
largest features on earth. Okay.
Massive earthquakes and tsunamis are
also quite common in these situations.
And we're gonna get into why again
how Tsunamis come about. But i mean when
you have a plate jamming itself
underneath another plate you're gonna
get massive earthquakes. And here's that
trench where this is happening, this is
the Pacific plate happening right here,
and it's just jamming itself into that
trench. Alright, the third way that you
can move things together is by colliding
two bits of continental crust. Okay. So
when that happens there's no subduction.
So continents tend to just pile up on
top of each other. It just turns into
just a huge mess. And the result is huge
mountain chains. Right. So you can't get
one to really go down, I mean you can
force one on top of the other
it's not gonna recycle itself and subduct itself down into the earth and
become part of the mantle again, they'll
just simply layer on top of each other.
They'll pile up and though deform. The
rocks will fold, large faults will form,
and you'll create these massive chains
of mountains. The Himalaya are an example.
The Alps and the
Appalachian Mountains in the United
States all formed in this way. What we
see here...this is an image, this is the
Indian plate that's colliding with the
Eurasian Plate right here...and what's
going on is...in fact it's moving in this
direction Eurasian Plate is moving
roughly in the southerly direction...and
as they collide into one another, massive
faults are forming right along this edge
right here, and pushing and ramping a
huge amount of rock straight up. Mount
Everest is located right here at 29,000...
now there it is....29,029 feet. I challenged you
earlier to check my altitude but
there it is. It's located right here. To
give you another idea, this is the inset
over here of that location is right here
showing you how tall these things are.
These mountains are tall, they're rugged.
Massive earthquakes are very common
along these types of plate edges and
they're very, very dangerous places to
live. There could be large
landslides, there's flooding events, and
of course the earthquakes are a major
problem as well. This entire part here,
the Tibetan Plateau, has been crushed
between Asia and India as they've been
colliding one with another, and so the
entire area has been lifting itself up.
Normally rivers and lakes tend to try to
find a way to drain out to the ocean,
well as these faults, and as this stuff
rises up, it actually pinches off the way
for this water to get out. So you have
permanent lake systems setting
themselves up here on top of the Tibetan
Plateau. There's no external drainage is
what I'm trying to say. These mountains
are rising so fast they're preventing
the rivers from successfully draining
these areas. Alright, so we talked about
the way that plates can move away from
each other and how they can move towards
each other. There's a third way that they
can move which is side by
side.
Okay. Those are referred to as transform
plate boundaries. And in a lot of ways transform plate boundaries are
the most benign but they also tend to be
in an areas that human beings like to
populate a lot. City of Los Angeles
immediately comes to mind as a place
where this happens.
So transform plate boundaries: where two
plates meet slipping and grinding past
one another.
Friction spawns earthquakes along
strike-slip faults. A strike-slip fault
means that you've got two faults, er
you've got two two sides of the earth or
two sides of the crust, and they're
trying to slip and every once in a while the
friction releases and BOOM it moves
very, very quickly. Now the types of crust
doesn't, don't matter as much as in
collisions. In collisions, if it's
oceanic or if it's continental it's a
really big deal. It turns out, for example,
the San Andreas Fault is moving oceanic
crust for the most part right adjacent
to continental crust. So there are two
different kinds of crusts and very close
proximity moving one past each other. And
in fact there's some transference, a
little bit of North America is sometimes
transferred over to the to the Pacific
crust side, or to the Pacific plate side
and vice versa. So it's not a
simple situation but you get the idea
here. And what we see here, is on this
side of the fault, this is the San
Andreas moving right through here...this
is the Carrizo plane which is located
just north of Los Angeles...and here this
entire side is moving in this direction,
this side is moving in this direction,
and we can even see that this river
right here, this wash, is moving across...
it's actually doglegged as it's trying to
keep up with the motion of the fault.
So whatever the fault moves it actually
cuts off, or what we call "beheads"
portions of this. So you can see old
places where the river used to be as we
cut off and translate it up over here as
it's slid.
So, it's kind of cool. So plate tectonics
is a big deal.
I mean, it's responsible for all the
landforms that we see or most of the
landforms that we see, tectonics builds
mountains, it shapes the geography, it
tells us where the oceans are going to
be, it determines where a lot of the
islands and continents are going to be
located on earth, and it gives rise to
earthquakes and volcanoes all of which
are important natural phenomenon that as
environmental scientists we need to keep
track of. Now topography created by
tectonics also shapes climate. So when we
talk about topography, this is changes in
elevation...where the mountains are that's
a change in the topography. So high
typography means areas that are of high
elevation. Areas of low topography of
areas of low elevation. So if it turns
out that if you have mountain ranges in
the way, that alters the patterns of rain,
wind, currents, heating, and cooling. So for
example, here we have mountain ranges
here...and this is the Gulf of Mexico
taken by Google Earth image...and we see
the Sonoran Desert located right over
here. But notice that we have an area of
green located over here on coastal
Mexico. And that is largely a phenomenon
of the topography. And of course that
affects the location of biomes. Where
things live, where plants and animals
live. Different things live here than
live here as a consequence of where
those mountains are. Alright, so we've
been talking about rocks and minerals...
let's do a quick discussion, I mean super
quick discussion of what a rock and
mineral is. So a mineral is any element
or inorganic compound, has a
crystalline structure, a specific
chemical composition, and distinct
physical properties. So it's something
that has always got the same stuff. So
silicon dioxide is quartz. SiO2. It's
always going to be SiO2. That's what they
mean by it having a specific chemical
structure. And they're crystals, and they
have distinct physical properties. We
know their hardness, we know something
about their color, you get the drift. Here
are some really amazing...these are both
of these are in fact are opals here. This
is a luz opal. it has something called
a galaxy inside. It's an incredible
little feature. I found this just surfing
on the web and I wanted to share it with
you. And then there was another one on
the same website over here, this is a
rounded sunset fire opal. Again these are
hy-, these are minerals...
they're hydrated silicon dioxide
minerals called opal.
That makes this amazing color. It turns
out there are thousands of minerals, but
we just wanted to simply mention what
they are. It's where all those atoms that
we talked about in the previous lecture
wind up on earth. Okay. Now a rock, by
contrast with a mineral, is an aggregate...is an aggregation of minerals. So it's
one or more minerals or it's actually
several minerals...so an aggregation of
two or more I should say...minerals in a
single substance. So these are rocks
right here, right. There's actually some
pretty interesting stuff happening here,
but you can see that these little bands
in here, these are little microscopic
crystals that we see everywhere
that create all of these rocks. And in
this case this looks like a nice piece
of opal rich material over here, rock
called a chert, all of this
are accumulations or agglomerations of
minerals into single blobs of material
that we call, in this case, a cobble. So
these are cobbles that are probably
washed along a beach. Again this is a
figure I found online and I just liked
it and wanted to share it. Now it turns
out there's three different kinds of
rocks on earth.
There's igneous rocks, there's
sedimentary rocks, and metamorphic rocks.
And you probably have heard of those
different rock types before, but we're
gonna go over them just briefly. So
igneous rock is formed when magma cools.
Igneous rocks are what we can think
of as "born of fire." Even has the word, the
I-G in there. It comes to us where we
get the word ignite and all these other
things from the same prime root as fire.
So igneous rocks form when magma cools.
Magma is just simply molten, liquid rock
within the earth. So intrusive igneous
rock is magma that cools slowly beneath
the earth's surface.
Granite's form this way. This is where
the liquid doesn't...it's liquid down
in the earth, but it doesn't make its way
to the surface. It cools down below, and
if it cools down below it'll crystallize
into nice beautiful rocks like granite.
So here's an example of a place where
that might happen. A laccolith is a place
where we might expect for this to happen.
We might have a sill that comes in and
fills in a blister of magma and that
magma never makes its way
into the surface. So it crystalizes down
below. Whereas we have extrusive igneous
rock: this is magma ejected from a
volcano.
So basalts like in Hawaii. Those
black lava, er...those black rocks that we
see in Hawaii are extruded or extrusive
igneous rocks. And those wind up at the
surface. And that can also result in
steam, gas, ash, create volcanic craters,
lots of stuff going on with volcanoes.
And by the way, there's a whole lecture
that I have on my Earth Science X
website or I'm sorry YouTube channel...
check that out...
on volcanoes if you're interested in how
volcanoes work. Lava, of course, is the
same thing as magma except it's magma
that is released from the lithosphere.
So once magma comes out of the magma
chamber, in this case of a volcano and makes
its way to the surface, these gasses
separate out and the lava is the liquid
portion that comes out of the magma. So
the magma is the combination of lava
plus the gases whereas when it gets to
the surface the lava separates out. So
that's reason why we have different
terms for them. Sedimentary rocks...I have
to admit I'm a little bit biased, I
really love sedimentary rocks. These
are rocks that are born of wind
and water. They're amazing. They come in
such a wide variety of colors, the
minerals that we showed you...the luz
opal and the fire opal...are actually from
sedimentary rocks. And they are
absolutely amazing.
So sedimentary rocks are formed when
sediments are compacted or cemented...
which is to say dissolved minerals
crystallize and bind together. So typical
forms of sedimentary rock include
sandstone, limestone, shale, mudstones. You
can think of all of those things as
sedimentary rocks. And what happens is
when you get little bits of material...and
sometimes fossils are included in that...you can compact and lithify and
create a rock...by the way that process is
called lithification...and frequently
they exhibit clear layering. Now you
don't normally find layering in the
traditional sense in igneous rocks. You
might if you look at the ash flow layers,
that can happen, but
traditionally we think of layers as a
sedimentary feature. So this is a
photograph of Bryce Canyon National Park.
this is a absolutely amazing place to go
and visit and hike around. You can check
it out in a day. These beautiful
spires are caused by differential
erosion happening in sedimentary layers.
And probably the prettiest, and granted
that's a very subjective thing to say,
but the prettiest rocks are the
metamorphic rocks. These are born of heat
and pressure. High temperature tends to
reshape crystals. I mean, if you take it
if you take a crystal and you put in our
enough heat it'll do one of two things:
it will either melt or it'll recrystallize
to something that is more...how would you
say...more stable at those higher
temperatures. A classic example of
minerals that do this is diamond and
graphite. Graphite at the Earth's surface
is perfectly happy but diamond is this
very hard, dense material but it turns
out that it's actually really happy
being at high pressure and high
temperature within the earth. And so it
will degrade into graphite at the
surface if it can. Now, if I take graphite
and I put it under extreme heat and
pressure and put it back down into the
earth it will convert into diamond.
Okay, now the real rule for this, or the
big rule for this is I can't put it
under such high heat that it melts. It
has to be at high pressure and high
temperature but not so high that
it actually melts it. Okay. A common
feature that we see in metamorphic rocks
is banding or foliation. So common
metamorphic rocks include marble...which
is actually pressure and heated
limestone...and slate...which is heated and
pressurized shale. These are types of
metamorphic rocks called banded gneisses.
They're actually in a big pile of
boulders. I'm not exactly sure where this image
was taken, but they're all banded
gneisses which are really beautiful,
high-grade metamorphic rocks. These have
been under very high pressure and
temperature.
Alright, so we mentioned all of that to
kind of get to this concept here. We
talked about how plates move together,
how plates pull apart, how they slide
past one another, the different...the three
different kinds of rocks, and what we
wanted to do is show that those are all
connected. That there's a relationship
that exists between all of them. That the
earth is in fact not only just recycling
crust all the time, especially oceanic
crust, but all the rocks within it as
well. And so that results in something
called the rock cycle which is the
heating, melting, and cooling, breaking, and
reassembling of rocks and minerals
over very long periods of time. So rocks
and minerals are constantly being
reformed and recycled on earth. It's
happening right now. What do you think
volcanoes are doing? Right. Volcanoes
are forming new rocks today. Mid-ocean
ridges are spreading and volcanic
material's coming in. Subduction is
pulling rocks back into the earth; it's
recycling this right now as we sit in
the environment that we're watching this
video on. And understanding the rock
cycle helps us appreciate the formation
and conservation of soils, minerals,
fossil fuels, and other natural resources.
When we think about soils we don't
necessarily think about how long it's
been there or what it takes to make them
or what type of rock is required to
exist for that type of soil to form, so
we have to be kind of mindful of these
things. And so the rock cycle is right
here. Over here to the right we actually
see the rock cycle as is deployed
in a convergent plate boundary. This is
where we see an oceanic crust being
subducted beneath a continental crust.
And so here we have sedimentary rock,
this is sedimentary rock, these are
sediments that are washing in through
rivers out of these mountains, the
sediment is coming in on the beach it's
actually falling down into what is
eventually the trench, it's being
compacted, so it's going under pressure,
as it's being put under pressure it's
being pulled through this conveyor belt
system, right. Because we have subduction
happening, it's now being converted in a
metamorphic rock. As it's going under
higher pressure and temperature...it might
be uplifted, we might actually see it up
over here...but as it goes from
metamorphic it'll transition into a
melting zone, that melting metamorphic
rock will then turn into igneous rock,
that
this rock will then go up into the
volcanoes, and the volcanoes will then
suddenly be subjected to
weathering, that weathering will then
result in the formation of sediments, and
it'll cycle back through this process
over and over and over again. So that's
what we mean by the rock cycle and it's
connection to plate tectonics. And, by the
way, all of the different plate
boundaries have forms of the rock cycle
happening around them. Alright. So
really quickly, I would like to talk
about some of the phenomenon that
happened at these plate...at these plate
boundaries and chief amongst them is
earthquakes. Those are pretty uniform at
all the different plate boundaries.
Sometimes they're large, sometimes
they're small. So all an earthquake is is
a release of energy along a plate
boundary or a fault.
Right. So faults are where energy is
being transmitted across the landscape
from one boundary...frequently from one
boundary to another. That can be along
a transform fault for example. They
can do tremendous damage to life and
property. This is actually an image of
a earthquake that happened, a 6.6 in central Italy that happened, and
you can see what that magnitude 6.6 did
to this town. It was absolutely
destructive. Now buildings can be built
or retrofitted to decrease damage and
buildings are designed....er the buildings
are not designed to be flexible. I mean
we can design them better, right. We can
design them to swing. What's really
interesting is this clock tower actually
survived and I believe the clock tower
had some seismic countermeasures built
into it if I can remember from the
original news article that I saw this
image in. It's expensive. Buildings in many
poorer nations do not have such
protections. Now another thing that we
see over and over again are volcanoes.
So volcanoes are formed when molten rock,
hot gas, or ash erupts through Earth's
surface, cooling, and creating a mountain.
Up here we actually see an image of
a volcano called Mount Unzen. We see this
cloud coming off of it. It turned out
this is something called a pyroclastic
cloud or a pyroclastic flow. So what
happens is that lava can flow
slowly or erupt suddenly, right. So
there's different ways that lavas flow.
And if, when you go into my series on
Earth Science X and study the origins of
volcanoes, the origins of igneous rocks,
you'll understand what I mean by how...
different ways that lava chemistry can
affect the explosiveness of a volcano.
Now one thing that we do know that is a
big deal are these pyroclastic flows.
These are fast-moving clouds of gas, ash,
and rock and they can kill people and
they do all the time. In fact, this
particular event that was caught on a
news camera did kill people. We actually
see this guy here running from it as
this thing piles into the town. Right, so...
and this is from Mount Unzen in
Japan, 1991.
So volcanic eruptions exert
environmental impacts. Ash blocks
sunlight, sulfur emissions lead to
sulfuric acid blocking and radiation
cooling the temperature. But that's
natural. This happens all the time. What I
want to do is I want to show you this
animation of this pyroclastic flow
while this, this guy runs away from it. So
it's coming down into the town
and they are just driving as fast they
can to get away from it.
It's gonna cut off here in a
moment.
Okay, so these things are extremely
dangerous and they're hot, that's
full of ash, this ash is extremely toxic
to human beings and so it's...it's
dangerous stuff.
Another thing that tends to happen is
landslides, right. When you have big
mountains in the area what goes up must
come down. And so if you have large
amounts of material that's standing
really, really high sometimes you don't
need to wait for the wind or
the water to come and wash it. Sometimes
gravity just takes it. So that's a
landslide. This is where we see something
called a severe, sudden mass wasting. This
is mass just wasting its way down the
hill slope. Large amounts of rock or soil
collapse and flow downhill. So mass
wasting is the downslope
movement of soil and rock due to gravity.
So, rain-saturated soils can trigger
mudslides. That's one form of mass
wasting. Mass wasting is the erosion of
unstable hill slopes and tends to damage
property. Caused by humans when soil is
loosed or exposed, and can cause massive
damage. Mudslides after Hurricane Mitch
killed over eleven thousand people in
1998. Let's look to see what this, this
slide is because if you saw one
happening you might think yourself "well,
I can just get out of the way of it." Well
watch this. You actually see it moving,
and the entire hill slope is now moving
at a very high speed. You can't run past
that. And if you got caught in it you
would almost certainly be killed.
Yeah. Another important phenomenon that
we're really developing an appreciation
for right now are tsunamis. So tsunamis
tend to follow earthquakes, volcanoes, and
landslides, and all it is is simply a
surge of seawater that's caused when
huge volumes of water are displaced by
earthquakes volcanoes or landslides.
That's what they are. So you can have a
large landslide that goes into the ocean,
it's gonna create a giant wave when that
happens. The damage can be really
widespread, and often across to distant
coastlines. So here we actually see the
tsunami aftermath...this all used to be
forested area, in fact there were people
living here, there was a city down here...
it's been completely wiped away by a
tsunami that came in here and ripped
this entire forest right back out to sea.
This was the December, 2004 the...December
26th 2004...tsunami event that came in, and
I believe over 1/4 million people lost
their lives; not just here but across the
world, cross the Indian Ocean as a
result of that tsunami. It was an amazing
force of nature that
went out that day.
Coral reefs, coastal forests, and wetlands
can be damaged. I mean, there's
nothing here, right. If there was any
coral reef here it's, it's definitely
been impacted. Salt water
contamination makes it hard to restore
them. I mean if you have a bunch of
freshwater here and you dump a bunch of
salt water on it it tends to damage this
coastline. Alright. It takes a while for
it to flush all that out and you can you
can see the mess that comes from this.
Agencies and nations have increased
efforts to give residents advanced
warning of approaching
tsunamis, and preserving coral reefs and
managing mangrove forests decreases the
wave energy of tsunami. So nature has a
way protecting these coastlines
naturally. So if we're not out there
ripping up the coastline and taking care
of...instead we take care of the reefs, we
take care of the mangrove forests that
grow right along those coastlines...the
tsunamis, while they still will do damage,
won't be as impactful as they ordinarily
would be. That's the idea that
they're trying to convey here. Alright.
now there are things we can do to worsen
this
situation for ourselves, right. So we just
 have to face the fact that, you know,
we have to deal with natural hazards. There's
floods, coastal erosion, wildfires,
tornadoes, and hurricanes that just
happened on earth. And it's just
something we have to deal with. When we
look at this picture of Honolulu, we
could see where the buildings are, the
hotels are right there on the water. This
is not a city that is set up for
protection against a major tsunami event,
right. If they got hit with a tsunami it
would be extremely devastating. Another
issue is our overpopulation. People must
live in susceptible areas. Honolulu is a
very, very large city on a very small
island in the middle of the Pacific. And
the Hawaiian island chain, Oahu, which
is where Honolulu is, it is one of the
smaller islands. It's it's certainly not
nearly as big as the biggest
island of Hawai'i. Most the other islands
are bigger. So but we choose to live in
attractive but vulnerable areas. We like
beaches, we like to live in the mountains,
and so there's consequences that come with
that. Engineered landscapes increase
frequency or severity of hazards. You
know, you build along a river across a mountain
chain, that roadside or that highway
is just going to absolutely cause
landslides, and there's gonna be flooding
events and all kinds of things. You dam a
river, you suppress fire, mining issues
will tend be a major issue, and of course
changing climate through greenhouse
gases changes rainfall patterns,
increases droughts, fire, flooding, and
storms. We've been seeing that especially
in the Darfur region of North Africa.
This is a major issue with climate
change. But there are things we can do
that mitigate the impacts of these
natural hazards, right. Through smart
engineering, right. We can build proper
sea walls that will defend against
coastal erosion. That's what we see right
here. This is a massive seawall that has
been constructed and you can see the
people are living right along the edge
of this thing. Now a tsunami hit it
that's another story,
but just a regular sea storm during just
a typical weather event it could
probably take it. We could build more
earthquake resistant structures. They're
expensive and third world countries
can't always afford to pay for them, but
that's one thing we can do. We design
early warning systems. This is something
we're starting to do more with tsunamis.
Volcanoes were working on it. We're
getting much better at predicting
volcanic events than we once were.
Tsunamis we're getting much, much better
at. Still, there's too many people losing
their lives in these events. We could
preserve reefs and shorelines, we can
have better forestry, agriculture, and
mining to prevent mass wasting
events. Some people would argue that
better regulations need to be imposed.
Building codes, insurance incentives
discourage developing in vulnerable
areas. Right now we use insurance,
especially government insurance, to
encourage people to build in flood prone
areas. It's the flooding...in the
United States...called the National Flood
Insurance Program where we actually
subsidize insurance for people to live
in dangerous areas. That might not be the
best thing for us. Right. So mitigating
climate change may reduce natural
hazards over time. Alright, so that's
just my quick introduction. It's a primer
to the earth and plate tectonics in
general, and how it's all kind of tied
together. And everything in
environmental science is happening on
that canvas. Now what we're going with
this now is into evolution and
biodiversity, because on that canvas of
the earth is life. What is life doing in
response to the changes on earth that's
where we get into evolution and
biodiversity. And we'll leave
you off with this image here from
Charles Darwin's image from nineteen...I'm
sorry...from 1845 where he was looking at
the finches of the Galapagos Islands. And
we'll see you in the next video. Take
care!
