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 WeatheringWhat 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:

Name the agents of mechanical weathering:

Plant Growth

Release of Pressure

Freezing and Thawing

Abrasion

Animal Actions

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 ORGANISMSAs 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

ACID RAINRainwater 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.

OXYGENThe 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 DIOXIDEAnother 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.

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.

SOILWhat 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?