Weathering and Soil Formation

Chapter 8

Section 1: Rocks and Weathering

• Review:• What are mountains made of?– Rocks

• How are rocks made into mountains?– Plate tectonics

• What do you think happens to rock once it is exposed to the surface of the Earth?– Weathering and Erosion

Weathering

• Weathering is the process that breaks down rock and other substances at Earth’s surface.

• Heat, cold, water, ice, oxygen, and carbon dioxide are elements of weathering.

• What are some examples?

Erosion

• Weathering breaks down rock…• Erosion is the removal of rock particles by

wind, water, ice and gravity.• Weathering and erosion work together to

break down and carry away rocks at Earth’s surface

Uniformitarianism

• Uniformitarianism is the principle that states that the process we see today are the same as those in the past.

• This is how scientists make hypotheses about things that occurred in the past.

2 kinds of Weathering

• Mechanical Weathering is when rock is physically broken into smaller pieces.– Smaller pieces are the same composition as the

larger pieces– Takes long periods of time– Can break down mountains!

Causes of Mechanical Weathering

•Freezing, thawing, release of pressure, plant growth, animals, abrasion

Abrasion

•Abrasion is the grinding away of rock by particles carried in wind, water, ice, or gravity.

Abrasion

Ice Wedging

• Ice wedging is the process of liquid water settling into cracks in rocks, freezing and cracking the rock as it expands

Ice Wedging

Chemical Weathering

• Chemical weathering is the process that breaks down rock through chemical changes.• Causes include action of water,

oxygen, carbon dioxide, living organisms, and acid rain

Chemical Weathering

• Chemical weathering can change or produce new minerals as it breaks down rock–Example: granite is made of several

minerals (feldspar, quartz, & mica)–During chemical weathering, the

feldspar minerals are changed to clay minerals.

Chemical and Mechanical Weathering Work Together

• Chemical weathering creates soft spots or holes in rocks so the rock breaks apart more easily• Chemical and mechanical weathering

work together how?–Mechanical weathering creates

more surface area to be exposed to chemical weathering

Review

• Weathering is?–the process that breaks down rock

and other substances at Earth’s surface.

• Erosion is?–the removal of rock particles by

wind, water, ice and gravity.

• Uniformitarianism is?– the principle that states that the

process we see today are the same as those in the past.

• Mechanical Weathering is?– when rock is physically broken into

smaller pieces.

What is this an example of?

What is this an example of?

• Chemical weathering is?– the process that breaks down rock

through chemical changes.• Chemical and mechanical weathering work

together how?–Mechanical weathering creates more

surface area to be exposed to chemical weathering

On your own

• Read about the 5 types of chemical weathering.• In the same notes we have

been working on, tell how each of these elements helps to break down rock.

Chemical Weathering

• Water: dissolves rock• Oxygen: when in contact with iron it

oxidizes (rusts) makes rock crumbly and brown/red.• Carbon dioxide: dissolves in water

and creates weak acid (carbonic acid). Easily weathers rocks

Chemical Weathering

• Living Organisms: Plant roots can produce weak acids that break down rock• Acid rain: chemicals from burning

fossil fuels (sulfur, carbon, nitrogen) combine with water vapor and fall as acid rain. Acid easily breaks down rock.

• Slate tombstones from the 1700s are less weathered and easier to read than marble tombstones from the 1800s.•Why?

Slate vs Marble

Rate of Weathering

• Factors that affect the rate of weathering are the type of rock and the climate.• 1. Type of rock: –type of minerals determine how

fast a rock weathers–Permeable rocks (those with air

holes) allow water to seep in

Rate of Weathering

• 2. Climate: Average weather in an area–Both chemical and mechanical

weathering occur faster in wet climates.–Chemical reactions occur faster at

higher temperatures–Hot, wet climate = faster rate of

weatehring