Rock weathering breaks down Earth's crust through physical and chemical processes. Physical weathering breaks rocks into smaller pieces through mechanical means like temperature changes, plant and animal activity, and abrasion. Chemical weathering alters the chemical composition of rocks through reactions with water, oxygen, carbon dioxide and acids. The rate of weathering depends on factors like climate, rock type, and exposure. Weathering produces sediments and soils that cover much of the Earth's surface.

1. WEATHERING
The Riverdeep Academy
Ms. Wenslette Imee C. Balauro

2. Weathering
The surface of Earth's crust, called lithosphere,
is constantly changing. Rocks break up into smaller
pieces in a process called weathering. This occurs
whenever rocks on or near Earth's surface are
exposed to air, water, and living things.
Weathering can be classified into two general
types: physical and chemical.

3. Physical Weathering
Weathering can break a large, solid
mass of rock into loose fragments. The
process of breaking down rocks without
changing their chemical composition is
called physical (or mechanical) weathering.
There are some factors that cause
physical weathering. Human activities and
movement of plants and animals can cause
rocks to fall apart. Abrasion, exfoliation,
change in temperature, and rain can also
trigger physical weathering.

4. Causes of Physical Weathering
Movements of plants and animals cause rocks
to break apart into smaller pieces. A seed may find
its way into a crack in a rock and germinate there. As
the plant grows, tiny rootlets go deeper into the
crack in search of water. The growing rootlets
thicken and press against the sides of the crack,
widening and extending the crack. Over the years,
the rock gradually breaks apart.
As roots of mosses and lichens grow and decay,
they produce an acid that dissolves rock particles.
This process further accelerates the breaking up of
rocks.

5. More than 100 years ago, English scientist
Charles Darwin (1809-1892) calculated that
in 1 acre of land, earthworms bring as much
as 10 metric tons of rock particles on its
surface each year.
Ants, termites, woodchucks, moles,
and other burrowing animals also
contribute to physical weathering. The
burrows that these animals create allow air
and water to penetrate deeper beneath the
Earth's surface, weathering the underlying
bedrock.

6. Mining is the extraction of valuable
materials, or deposits, beneath the
ground. Examples of these materials
are metals, coal, and limestone.
Surface mining removes layers of soil
or bedrock to reach the buried
deposits.

7. Abrasion
Abrasion is a major cause of physical
weathering. Rocks can break apart by
abrasion or by rubbing against each other.
Abrasion commonly occurs when rock
fragments are being carried along by agents
of erosion, such as water in streams or rivers.
As the fragments are carried along by the
water, they bounce off and rub against each
other. Wind also weathers rock by abrasion.
Anyone who has sat on a beach on a windy
day can attest to the abrasive power of wind-
driven sand.

8. Exfoliation
Another common cause of physical
weathering is exfoliation which is the
scaling off or peeling of successive
shells from the rock surface. Exfoliation
generally occurs in Coarse-grained
rocks that contain the mineral feldspar.
Whenever the surface of such rocks
becomes wet, moisture penetrates
pores and crevices between the
mineral grains and reacts. Note that
exfoliation is a physical process caused
by a chemical change. With successive
wettings of the rock surface, the
process is repeated.

9. Changes in Temperature
Rocks are exposed to constant
temperature changes. As rocks heat up
during the day, they expand. As they cool
off at night, they contract. You might think
that the usual heating and cooling off of
rocks cause them to crack and break up,
but studies have indicated that this is not
generally the case. Only extreme
temperature changes, such as those
resulting from forest and brush fires, cause
rocks to crack or flake off at the surface.

10. Chemical weathering changes
the chemical composition of rocks.
The minerals that make up the rock
undergo chemical changes, which
result in the weakening and the
breaking down of the rock.
The most common causes of
chemical weathering are water,
oxygen carbon dioxide, and acids.
Chemical Weathering

11. Water
Water can dissolve many minerals. As
water dissolves the minerals. rocks may
either change in composition or fall apart.
For instance, when the mineral feldspar
combines with water, it changes to a clay
material called kaolinite. Water may also
combine with some gases in the air to
form an acid that can change the
composition of the rock that comes in
contact with it.

12. Oxygen
Some rocks contain the element
iron. When these rocks are exposed
to air, the iron combines with
oxygen to form iron oxide, or rust.
This process is called oxidation.
Rust weakens the rock, causing it
to eventually crumble.

13. Rainwater reacts with substances
present in the atmosphere and form
different kinds of compounds. For
example, when rainwater reacts with
carbon dioxide in the air, a weak acid
called carbonic acid is formed.
Carbonic acid, as it drains on the
ground, dissolves some minerals present
in the rocks. This acidic water is more
effective than pure water in dissolving
some minerals. Consequently, the rocks
crumble into smaller Fragments or fine
particles called soil.
Carbon Dioxide

14. Acids
Sulfuric acid is formed when water
vapor combines with sulfur dioxide
in the air. Sulfuric acid is a strong
acid that easily dissolves rocks and
their minerals.
The acid produced by mosses and
lichens also cause chemical
weathering as it dissolves rocks
and minerals.

15. Factors Affecting the Rate of Weathering
How long does it take for a rock to be broken apart
by weathering process?
The answer is complex since many factors
influence the rate at which a rock will weather. The
main factors affecting weathering are climate,
particle size, mineral composition, exposure to
weathering elements, and time.

16. Climate
Climate is the average condition of the
atmosphere in a region over a long period
of time. Chemical reaction usually occurs
at a faster rate as temperature increases.
Many of these reactions require the
presence of moisture or water. Thus, a hot
moist climate supports increased plant and
animal activities, ranging from burrowing
production of rock- to the pro dissolving
acid as plant matter decomposes. This type
of climate is a favorable condition for rapid
chemical weathering.

17. Particle Size
The size of rock particles greatly
affects the rate at which chemical
weathering occurs. Under the
same conditions, the smaller the
pieces of rock fragments, the
faster they will weather. Given the
same volume of large and small
particles of rocks, the smaller
pieces of rock fragments will
undergo weathering faster than
the larger pieces of rocks.

18. Mineral Composition
The mineral composition of a rock
determines its physical and chemical
properties and thus its susceptibility to
weathering.
This factor greatly affects chemical
weathering. Rocks composed of minerals that
react readily with acids, water, or oxygen will
weather more rapidly than those composed
of less reactive minerals. For example,
limestone, which is mostly calcite, is
dissolved by mildly acidic rainwater since
calcium carbonate, of which calcite is made,
has high solubility in water.

19. Exposure refers to the degree to
which a rock comes into contact with
weathering agents. Soil, ice, and
vegetation can cover a rock and.
thereby, decrease its contact with
weathering agents. Covered rocks
tend to weather more slowly than
those that are completely exposed at
the surface.
Exposure to Weathering Agents and Time

20. Products of Weathering
Rocks exposed on the surface of Earth are acted
upon by forces that cause them to disintegrate. Solid
rock is broken into fragments by physical or chemical
forces. These fragments range from the tiniest
particles dissolved in water to the largest boulders.
The fragments produced form sediments and soils.

21. Sediments
The fragments or particles of
rocks produced by weathering
are called sediments. These are
classified according to size.
Table 10.1 gives the types of
sediments and their
corresponding particle diameter
in centimeters (cm).
Type of
Sediment
Particle
Diameter (cm)
Clay <0.0004
Silt 00.0004-0.006
Sand 0.01-0.2
Pebble 00.006-0.2
Cobble 6.4-25.6
Boulder >25.6

22. Soil is the accumulated loose weathered materials that cover much of the
land surface of Earth. Soil varies in depth, composition, age, color, and texture.
Soil is formed from weathered or broken down rocks over a long period of
time, a process that can take thousands of years or more. The surfaces of rocks
are constantly exposed to heat and pressure like wind and water, causing them
to break down gradually.
Soil

23. Soil is the accumulated loose weathered materials that cover much of the
land surface of Earth. Soil varies in depth, composition, age, color, and texture.
Soil is formed from weathered or broken down rocks over a long period of
time, a process that can take thousands of years or more. The surfaces of rocks
are constantly exposed to heat and pressure like wind and water, causing them
to break down gradually.
Soil

24. Have you ever wondered how the
quantity of soil is maintained?
You have seen that soil is formed
in many ways. If soil formation is a
continuous process, then why is it that
Earth is not getting bigger? While there
are areas on Earth on which soil forms,
there are also areas on which soil is
destroyed. These areas are called
subduction zones.

25. GOOD WORK!

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