Transcript What breaks down rocks?

As you observe the following pictures think about
this…
• Have the landforms undergone changes?
• What do you think caused the changes?
• How long do you think the changes may have
taken?
• Were the changes constructive or destructive?
Notes: Rocks and Weathering
What breaks down rocks?
Erosion – is the process of wearing down and carrying away
rocks. (breaking of rocks into smaller pieces and the removal
of rock particles by wind, water, ice, or gravity)
Weathering – is the process that breaks down rock and other
substances. (heat, cold, water, ice, and gases all contribute)
Both involve the breaking down of rocks into smaller pieces,
but erosion also involves the removal of rocks once they are
broken.
Erosion and weathering change Earth’s surface continuously,
or without stopping. They are destructive forces that act to
break and wear down the surface.
What causes weathering?
Mechanical Weathering – rock is physically broken down into smaller
pieces
Agents of Mechanical Weathering:
Release of Pressure
Name the agents of mechanical weathering:
Plant Growth
Abrasion
Animal Actions
Freezing and Thawing
What causes weathering?
Chemical Weathering – the process that breaks down rock through
chemical changes
Agents of Chemical Weathering:
WATER
Water weathers some
rocks by dissolving it.
Water also carries other
substances that dissolve
or break down rock,
including oxygen, carbon
dioxide, and other
chemicals
LIVING ORGANISMS
As a plant’s roots grow,
they produce weak acids
that slowly dissolve rock
around the roots.
Lichens – plantlike
organisms that grow on
rocks- also produce
weak acids
OXYGEN
The oxygen gas in air is an
important cause of chemical
weathering. Iron combines
with oxygen in the presence of
water in a process called
oxidation. The product of iron
oxidation is rust. Rust makes
rocks soft and crumbly and
gives it a red or brown color.
CARBON DIOXIDE
Another gas found in air.
Causes chemical
weathering when it
dissolves in water. The
result is carbonic acid.
Carbonic acid easily
weathers some kinds of
rocks, such as marble
and limestone.
ACID RAIN
Rainwater is naturally slightly acidic. Burning coal, oil, and gas
for energy can pollute the air with sulfur, carbon, and
nitrogen compounds. These compounds react with water
vapor in clouds, making acids that are stronger than normal
rainwater. These acids mix with raindrops and fall as acid
rain. This causes very rapid chemical weathering of rock.
LET’S REVI EW:
Mechanical – means by physical processes
(like a physical change – a change in size, shape, state; the
change does not alter the makeup of the substance)
Chemical – suggests processes related to chemical reactions
(like a chemical change – changes resulting from chemical
reactions, in which substances change into other
substances)
Chemical and mechanical weathering often work
together. Chemical weathering creates holes of soft
spots in rock, so the rock breaks apart more easily.
As rocks break into pieces, more surface area is
Exposed to chemical weathering.
How fast does weathering occur?
The most important factors that determine the rate at which
weathering occurs are the type of rock and climate.
Type of Rock
• Minerals in the rock determine how fast it weathers.
Rocks weather faster if they are made up of minerals that dissolve easily.
• Some rocks will weather faster if they are permeable – full of
tiny, connected air spaces that allow water to seep through it. As water
seeps through the spaces it carries chemicals that dissolve the rock.
Climate
• Climate is the average weather conditions in an area.
• Both chemical and mechanical weathering occur faster in wet climates.
Rainfall provides water for chemical changes and freezing and thawing.
• Chemical reactions occur faster at higher temperatures. So chemical
weathering occurs more quickly where the climate is both hot and wet.
SOIL
What are some examples of organisms that live in
soil?
Describe soil you have seen or touched. How did it
feel? How did it smell? What creatures did you see in
it?