APES Soil formation

Professor: Hey guys, let's have another,
uh, quick video on, uh, Earth systems,

we're going to talk specifically in this case
about soil formation, how do we get from

the rocks in the rock cycle that obviously
come from the, uh, crust and the tectonic

plates, how do we get from all that to the
soil that obviously is going to have a

pretty much direct impact on human and
really all biological life.

So, essentially what soil is, is soil is a
mix of geologic and organic components, so

you've got parts of the biosphere here,
um, that as they die and decay they get

deposited, uh, and of course their
manure and stuff like that, and then

you've got part of the Geosphere which
are the rocks being broken down.

You need both of these things together,
um, to actually make soil, so like if you

just have sand, things don't grow well in
sand, that's just a rock, um, and so for

it to actually become soil and to grow
you've gotta mix in organic

matter with that.

That's why if you've got a really sandy
soil, that's its usually necessary either

mix in some fertilizer or some manure
or some compost, something that gives it

some organic component, so that's really
what compost is, is compost is organic

components that are going to decay down
and then if you mix those in with the

rock components, some dirt, some clay,
stuff like that, then it can

become actual soil.

So, two parts here, you've got the break-
down of the rocks, you've got deposition

of organic matter, those two things
together are going to create soil.

So, we talked about the rocks and the
rock cycle, uh, the video we did before

this, um, the deposition of organic matter
again is, um, as things die and are broken

down by bacteria, uh, stirred up by
earthworms stuff like that, um manure

being deposited, all those things are
going to go into making

proper soil as well; and there are
basically, five factors that are going to

effect what the soil is like and we all
know that different kinds of soil are

going to be used it--er are going to be--
appear in different areas and going

to be used to grow different things.

So, the first thing is, is the parent
material, so what kind of rock, um, is

actually being broken down, and so, it's
a little hard to see in the video here,

but this topic example, this is some, uh,
granite, uh, and if that's broken down,

you tend to not really get super rich
soils because granite has a lot of

silica components in it, which is,
think about sand, um, and so that's not

going to be very nutrient rich just
from the rocks component, now of course

if you add an organic component to it
that's what makes it soil and that's

what helps out.

But on the other hand, if something
like say, limestone breaks down,

limestone is essentially calcium, um, and
so the calcium that's in that, um, is

going to actually be one of the active
nutrient components in the soil and so the

parent material is, what kind of rock
breaks down to actually form the rock

component, um, it's pretty important to
what the soil is.

Um, climate obviously has a pretty big
effect on this, um, the temperature

and precipitation, particularly are going
to affect how quick the soil forms, um,

soils not going to form very well
typically in really, uh, cold climates,

um, but in warmer climates, in
particularly climates where, um, you get

a lot of precipitation, therefore a lot
of weathering, a lot of erosion, um, a lot

of deposition, um from p-precipitation
then the soil is going to form much

more quickly and that's why in, uh,
tropical areas you tend to see much

richer types of soils, in the Tempa
regions obviously, as compared to

arctic regions, you are going to get much
better soil out of that.

Um, the third thing that is going to
affect the rate--er affect the soil

formation is topography, in other words,
how steep is the land, um, it tends to be

just generally speaking, that the steeper
the slope that the more quickly it's going

to erode because the higher up it is, the
steeper it is, um, the faster the water

is going to flow down it, the more it's
going to be subjected to wind, all those

things are going to weather and break down
the rock and then

lead to quicker soil formation.

Uh, what kind of organisms are in the
area, and so again this works against

arctic regions because there's not quite
the vast variety of organisms.

Um, and so plants and animals are going to
take nutrients out of the soil, uh,

bacteria and stuff are going to break
stuff down, earthworms are going to

help to mix up the soil and so all of
those things together, um,

are the organisms, the biological
part that's going to help to start to

make up the soil.

And the firth component, um, is time,
okay?

So, the longer the time goes, in general,
the more of what we call mature the soil

now, the reason that we call them
mature soil is because A, the particles

of the rock are usually broken down much
finer, and then secondly, there's going

to tend to be a lot more organic material
there.

So, like for instance, if we were talking
about like a volcanic island that just

So, if we were talking about like a
volcanic island that has just formed, um,

some of the rock might break down, but
until animals start to come there, and you

might get birds and stuff like that
obviously going by, but not you're not

going to have a lot of organic matter so
that's going to be a very immature soil.

As time goes on and that volcanic isle
ages a little bit, the rocks break down a

little bit more, more plant life starts to
come in, seeds get drawn by birds,

stuff starts to grow, break down the soil
more, it dies off and forms more organic

material and as time goes on you get
a much more mature soil out of that.

Okay, so, um, let's talk a little bit
about the layers in soil, um, layers in

soil are called Soil Horizons, don't let
that term like sort of throw you off,

Horizon means layer for us, um, and so
we've got some basic layers here.

So, we've got an organic, um, layer at the
top which basically just means at the

very top layer of the soil is essentially
just the plant life typically, um,

especially in a forest or grassland