Download Soil

Weathering
1
Weathering and Its Effects
• Together, surface processes that work to
break down rock are called weathering.
• Weathering breaks rock into smaller and
smaller pieces.
• These smaller, loose pieces are called
sediment.
Weathering
1
Mechanical Weathering
• Mechanical weathering occurs when rocks
are broken apart by physical processes. This
means that the overall chemical makeup of
the rock stays the same.
Click image to view movie.
Water that’s found in the cracks of rocks
can freeze. Once it freezes it expands
breaking the surrounding rock; ICE
WEDGING
Animals or insects that dig in the ground break up
rocks
Weathering
1
Chemical Weathering
• Chemical weathering occurs when chemical
reactions dissolve the minerals in rocks or
change them into different minerals.
• This type of weathering changes the chemical
composition of the rock, which can weaken
the rock.
Oxidation is a process that changes from one
type to another when the mineral, oxygen and
water reacts. alteration of the iron-bearing
mineral magnetite to a rustlike material called
limonite.
Weathering
1
Weathering and Its Effects
• Weathering wears mountains down to hills.
• Rocks at the top of mountains are broken
down by weathering, and the sediment is
moved downhill by gravity, water, and ice.
• Two different types of
weathering—mechanical
weathering and chemical
weathering—work
together to shape Earth’s
surface.
Murphy Marble Belt
Valley and Ridge
Blue Ridge
Talc, Slate, Shale,
Limestone
Fall Line
Piedmont
Granite
Kaolin, Sand
Coastal Plain
Mineral map of GA
Think About it….
• In what type of climate would the rate of
mechanical weathering happen the
fastest?
• In what type of climate would the rate of
chemical weathering happen the fastest?
Weathering
1
Effects of Climate
• Climate is the pattern of weather that occurs
in a particular area over many years.
• In cold climates, where freezing and thawing
are frequent, mechanical weathering rapidly
breaks down rock through the process of ice
wedging.
Weathering
1
Effects of Climate
• Chemical
weathering is
more rapid in
warm, wet
climates.
• Lack of moisture in deserts and low
temperatures in polar regions slow down
chemical weathering.
Quick Check
1
Question 1
Explain the difference between mechanical
and chemical weathering.
Section Check
1
Answer
Mechanical weathering occurs by physical
processes. Growing plants, burrowing animals
and expanding ice are processes that can
mechanically weather rock. Chemical
weathering occurs when chemical reactions
dissolve minerals in rocks or change them into
different minerals.
What is soil?
• Soil is a mixture of
weathered rock,
decayed organic
matters, mineral
fragments, water, and
air.
How is soil formed?
1. weathering breaks down
rocks or minerals on our
surface, it creates a
layer of rock sediments.
2. Over time, the
sediments break down
even more creating very
fine (small) particles.
3. Plants and animals add
organic matter, the
wastes and dead plant
material, to the rock
fragments.
• Soil can take
thousands of years to
form and ranges from
60 m thick in some
areas to just a few
centimeters thick in
others.
Soil Ecosystem
Sediment sizes
• Soils are classified
according to their
particle size as
follows:
Another look at the types of soils
Composition of Soil
2
• Rock and mineral
fragments, organic
matter, air and water.
• Animals and
microorganisms provide
additional organic matter
when they die.
• The decayed organic matter turns into a dark-colored
material called humus (HYEW mus). Humus serves
as a source of nutrients for plants.
Soil profile
• The top layer of soil
typically is darker
than the soil layers
below it. These
different layers of soil
are called horizons
• Most soils have three
horizons—labeled A,
B, and C.
The Nature of Soil
2
A Horizon
• The A horizon is the top
layer of soil.
• In a forest, the A horizon
might be covered with litter.
Litter consists of leaves,
twigs, and other organic
material that eventually can
be changed to humus by
decomposing organisms.
• The A horizon also is known as topsoil.
Horizon A: Wrap up
• Top layer of soil that’s covered with litter.
• The organic material can be changed into
humus which provides nutrients
• This layer is the very fertile and has few
rocks and mineral fragments
The Nature of Soil
2
B Horizon
• The layer below the A horizon is the B
horizon.
• Because less organic matter is added to this
horizon, it is lighter in color than the A
horizon and contains less humus.
• As a result, the B horizon is less fertile.
The Nature of Soil
2
B Horizon
• Leaching is the removal
of minerals that have been
dissolved in water. In soil,
water seeps through the A
horizon where it reacts
with humus and carbon
dioxide to form acid.
• The acid dissolves some of the minerals in the
A horizon and carries the material into the B
horizon.
The Nature of Soil
2
C Horizon
• The C horizon consists of partially
weathered rock and is the bottom horizon
in a soil profile.
• This horizon does not contain much organic
matter and is not strongly affected by
leaching.
• It is the thickest layer of soil
• What would you find if you dug to the bottom
of the C horizon?
• You would find rock—the rock that gave rise
to the soil horizons above it. This layer of
rock is called bedrock
• What are the climate types for the each
soil profile below?
• Why do you think the profiles are
different?
The Nature of Soil
2
Soil Types Reflect Climate
• Soils in deserts contain little organic material
and also are thinner than soils in wetter
climates.
• Prairie soils have
thick, dark A
horizons because the
grasses that grow
there contribute lots
of organic matter.
The Nature of Soil
2
Other Factors
• Parent material has an effect on the soils
that develop from it.
• Rock type also affects the type of vegetation
that grows in a region, because different
rocks provide different amounts of nutrients
for plant growth.
• Type of vegetation then affects soil
formation.
The Nature of Soil
2
Other Factors
• Time also affects soil development.
• If weathering has been occurring for only
a short time, the parent rock determines
the soil characteristics.
The Nature of Soil
2
Other Factors
• The slope of the land affects soil development.
Thin, poorly
developed soils
form on steep
slopes, but
valleys often
have thick, welldeveloped soils.
As gravity, a type of force of erosion, moves soil
and sediments downhill deposition occurs at the
bottom of the hill (slope). This is why the soil
formation is different in the two locations
Possible Sentences for
Soil
______________
Name of Topic
Word Box
soil
horizons
sand
bedrock
humus
leaching
silt
topsoil
litter
soil profile
clay
parent rock
Write 6 sentences by using two of the above words in each sentence. Do not use a word
more than once.
_____ 1. ____________________________________________________
____________________________________________________
____________________________________________________
_____ 2. ____________________________________________________
____________________________________________________
____________________________________________________
_____ 3. ____________________________________________________
____________________________________________________
____________________________________________________
_____ 4. ____________________________________________________
____________________________________________________
____________________________________________________
_____ 5. ____________________________________________________
____________________________________________________
____________________________________________________
_____ 6. ____________________________________________________
____________________________________________________
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Warm UP
• On a piece of paper you can hand in for a grade--• Write a paragraph to compare and contrast the
two soils from yesterday’s observations. Explain
why the soils looked differently and how
minerals/organic material got into the soil. Give
specific details and justify your answers with
details.
• You will have 15 minutes to
• complete this task.
INB Page 76
Complete the following Using your
Textbook
• List the 5 factors that affect soil formation (pg. 188).
• Next to each factor, use pg. 193-194 to explain how
that factor affects the formation of soil. (for example,
type of rock affects soil formation because the
minerals that make up the rock weather to form the
soil)
• On pg. 188, list the 5 components of soil (what the soil
is made of) and draw a picture of each component.
• Draw the soil profile on pg. 191 with the labels. Next to
each layer, list 3 important facts about the soil.
• Answer this question using pg. 193: Why do different
areas of the United States have different types of soil?
• http://www.epa.gov/acidrain/education/site_
students/acid_anim.html