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Joan Cartan-Hansen, Host: Soil
is more than just dirt.

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Without soil, there would be no
life on our planet.

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So, find out more about soil.

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[MUSIC]

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Cartan-Hansen: Soil is the top
layer of the earth.

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It's made of air and gas, bits
of rock, minerals, water,

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decaying plants and tiny
microbes.

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Soil forms in different layers
on the earth.

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When soil scientists study
layers of soil, they call it

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studying the soil profile.

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Topsoil is the layer you see,
the layer you typically walk on.

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It contains dark organic
material which is made up of

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decayed plant and animal matter.

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Topsoil can be about six inches
thick.

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Under topsoil is sub-soil.

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It's from several inches to
several feet thick.

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It looks lighter because it
contains less humus, is more

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tightly packed and has slightly
bigger pieces of rock.

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Next is the fragmented rock
layer or the parent material.

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Nothing grows at this layer.

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It's made up of rock particles,
sand, clay, salts and minerals.

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At the deepest level is solid
bedrock.

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This is the layer of rock from
which soil begins to form.

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Soil is created over lots of
time.

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Rocks form when volcanos erupt
or when sands get compressed.

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Weathering from wind, ice and
rain breaks rocks into smaller

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parts.

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Plants grow in the cracks caused
by erosion, creating more holes

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for air and water.

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They also drop leaves which
decay.

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Animals leave waste products
behind.

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Bacteria and fungi help break
down dead plant and animal

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materials into smaller pieces.

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These combine with rock
particles to make soil.

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Now, there are different types
of soil.

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The type depends upon the
original parent material, how

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big the rock particles are, the
climate and what else is in the

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mixture.

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Student One: Clay is the
smallest soil particle.

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Clay clumps because it can hold
water better than some other

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types of soil.

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Student Two: Silt is powdery and
soft to the touch and retains

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water well.

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Student Three: Sand is the
largest soil particle.

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It's the least resistant to
weathering.

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Student Four: Loam has the best
soil for growing plants.

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It is an even combination of
sand, silt and clay particles

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with organic materials.

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Cartan-Hansen: There are over
25,000 different named soils in

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the United States.

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Soil scientists are trained to
be able to identify different

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types of soil and what they mean
for the environment.

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Soil is very much alive.

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One tablespoon of soil contains
more microbes than there are

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humans on the earth.

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Insects, bacteria, earth worms
and other creatures live in

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soil.

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Larger animals do, too, like
badgers and snakes.

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Soil filters our water, holding
back contaminants and taking out

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impurities.

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Soil is used in construction and
provides the foundation upon

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which our homes and businesses
are built.

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And importantly, plants need
soils to provide them with

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minerals and nutrients.

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Soils scientists help farmers
understand what plants to grow,

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and how to improve the soil to
increase their crop yields.

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Student: Soil is an essential
natural resource.

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It's food for some animals and
home for others.

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Soil cleans our water, provides
nutrients for plants and gives

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us a place to live.

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So learn about soil.

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Dig in!

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Cartan-Hansen: If you want to
learn more about soil, check out

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the science trek website.

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You'll find it at science trek
dot org.

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[MUSIC]

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ANNOUNCER: Presentation of

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Science Trek on Idaho Public
Television is made possible

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through the generous support of
the Laura Moore Cunningham

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Foundation, committed to
fulfilling the Moore and Bettis

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family legacy of building the
great state of Idaho.

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By the Idaho National
Laboratory, mentoring talent and

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finding solutions for energy and
security challenges, by The

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Friends of Idaho Public
Television and by the

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Corporation for Public