Weathering and Soil Formation - 6th Grade Science with Mrs. Harlow

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Transcript Weathering and Soil Formation - 6th Grade Science with Mrs. Harlow

Rates
of
Weathering

Ch. 10 Section 2
Rates of Weathering
Hard rocks weather slower than soft rocks.
 This is also called differential weathering.

Devils Tower in Wyoming
Devils Tower in Wyoming
What Happened?
Long ago, magma cooled in the center of
a volcano to form igneous rock.
 Over time, the outer rock, softer rock
weathered away leaving only the harder
inner rock.

Think about it!

A rock will have a lower rate of
weathering when the rock
– A. Is in a humid climate.
– B. Is a very hard rock, such as granite.
– C. Is at a high elevation.
– D. Has more surface area exposed to
weathering.
Surface Area

Because weathering occurs on the surface
of rocks, the more surface area exposed
to weather the faster a rock will weather.
Climate affects weathering.

Climate is average weather condition in an
area.
Warm, humid climate
Chemical weathering
occurs faster in warmer,
wetter climates.
 Like Georgia

Water and Temperature

More water and lower temperatures affect
mechanical weathering.

If water freezes and thaws often then ice
wedging occurs more.
Mountain Tops

Mountain tops weather faster because
they are exposed to more wind, rain, and
ice.
Think about it!

Why does the peak of a mountain weather
faster than the rocks at the bottom of the
mountain?
Think about it!

Why does the peak of a mountain weather
faster than the rocks at the bottom of the
mountain?
– Answer: Rocks at the peak of a mountain
weather faster because they are exposed to
more wind, rain, and ice.
From Bedrock
to Soil

Ch. 10 Section 3
What is soil?

Soil is a loose mixture of small mineral
fragments, organic material, water, and
air that can support the growth of
vegetation.
All soil is different

Soil (weathered rock fragments) can be
made of many different types of rock. The
type of rock that the soil was made from
is called parent rock.
Parts of Soil
Bedrock
Bedrock is the layer of rock beneath the
soil.
 Some soil is made from bedrock, so it
remains above the parent rock.

Humus

Humus is the dark, organic material in soil
that is formed from decayed remains of
plants and animals.
Soil Horizons

Soil is usually layered with humus-rich soil
on top, sediment below that, and bedrock
on bottom.
Think about it!

What is the source of mineral fragments in
soil?

The proportion of different sized particles
in soil determines the soil’s
– A.
– B.
– C.
– D.
Texture
Fertility
Structure
Horizon
Think about it!

What is the source of mineral fragments in
soil? Parent Rock

The proportion of different sized particles
in soil determines the soil’s
– A.
– B.
– C.
– D.
Texture
Fertility
Structure
Horizon

Soil
Conservation
Ch. 10, Section 4
Soil Conservation

Soil Conservation is a method to maintain
the fertility of soil by preventing erosion
and the loss of nutrients.
Importance of soil
Soil provides nutrients to plant life.
 If the soil loses these nutrients then the
plants will not grow.
 All animals get energy from plants.

– How can unhealthy soil effect us?
Housing and Water
Soil is also important to providing shelter
for animals that live in soil.
 It also stores water for plants and animals,
and helps prevent flooding.

Can you tell which is grown in
healthy soil?
Land Degradation

When soil is overused it loses its nutrients.
How could soil be overused?
Land Degradation

When soil is overused it loses its nutrients.
– This can happen from poor farming
techniques or overgrazing.
Plants can’t grow in infertile soil.
 Without plants and moisture the soil can
be washed or blown away.

Erosion

Erosion is the process by which wind,
water, or gravity transport soil and
sediment from one location to another.

This happens when land is left
unprotected.
This happened in south Georgia long ago.
The result was Providence Canyon.
 What was once cotton fields is now a 150
ft. deep canyon.

Providence Canyon
Providence Canyon
Providence Canyon
Providence Canyon
Providence Canyon
Soil Conservation

There are many ways that farmers help
prevent erosion.
– Contour plowing
– Terracing
– No-till farming
– Cover crops
– Crop rotation
Contour Plowing
Terracing
No-till farming
Cover crops

Cover crops are crops such as soy beans
and peanuts that help restore important
nutrients to the soil and prevents erosion.
Crop rotation

Rotating crops from one year to the next.
Think about it!

Why is soil important?

How does crop rotation benefit soil?
Think about it!
Why is soil important?
Soil provides nutrients to plants; provides
houses for animals; and stores water.
 How does crop rotation benefit soil?
Crop rotation helps prevent soil nutrients
from being depleted. Alternation of crops in
the same soil reduces nutrient loss.
