Download Soil - drakepond8thgradescience

Earth’s Resources: Soil
What is soil?




The outermost layer of the earth’s crust
Made up of both organic (from living things)
and inorganic materials.
It’s divided into layers according to the ratio of
organic to inorganic material at various depths
It’s classified according to what kind of
material you can find in a sample
Layers of the soil


The layers vary as to
content
The closer to the top,
the more organic
material you’ll find




Leaves
Sticks
Dead animals (insects as
well as larger critters)
Finally, at the bottom,
you will hit BEDROCK!
Layers = HORIZONS


The topmost layer, or O
horizon, includes “litter” or
detritus from formerly living
things.
The A horizon is the most
valuable – It is the topsoil
where plants get most of
their nutrients. The decaying
organic matter in this layer is
called humus.
Humus





As living things (both dead plants and dead
animals) decompose, their molecular
components become available for new plants
to take up as nutrients.
This decayed material is called humus.
Humus is mostly insoluble, so it remains in
these upper layers of soil.
It is very dark, nearly black in color.
Human created humus is called compost!
TOPSOIL



Five tons of topsoil spread over an acre would
only be as thick as a dime!
It takes over 500 years for organic material to
collect and decompose naturally to form only
ONE INCH of topsoil!
5 to 10 tons of animal life can exist in an acre
of topsoil!
Layers = HORIZONS


The E horizon is
where the nutrients
from the organic
material (humus)
begin to dissolve.
The deepest of
plants’ roots
sometimes extend
this far.
Layers = HORIZONS



The B horizon (aka
subsoil)
This layer contains a
smaller amount of
organic material.
It has a heavy
concetration of the
minerals leached
from the above
layers.
Layers = HORIZONS



The C and R horizons
are the underlying rock.
C horizon is weathered
and broken rock or
regolith. Leached
minerals may be found
here.
The R horizon is
bedrock (almost solid
crustal material.)
Layers = Horizons




Soil in different locations may or may not have
all of these horizons
For instance, in a construction zone, all of the
topsoil may have been removed.
Topsoil may have eroded through wind or
water effects.
Heavy earthquake or storm damage may have
disrupted the existing layers
Other components of soil



Water – after rains or floods, water infiltrates
the soil, carrying the nutrients to plant roots
and into lower horizons
Air – soil is composed of approximately 25%
air, aided by the movement of worms and
insects in the topsoil layers
5% living things – plant roots, worms,
microorganisms make up part of the soil.
Leaching



After rain or other sorts of precipitation, water
moves into the soil. This is called infiltration.
As it moves from the topsoil layer into the
subsoils and deeper, it dissolves inorganic
minerals from the upper layers. This is called
leaching.
Minerals and other substances may be carried
into groundwater supplies and thus into
drinking water in this manner.