Weathering and Soil Erosion

Chapter 8 and 9

How Soil Forms

What is soil? Soil is the loose, weathered material on

the Earth’s surface which allows for plants to grow.

Bedrock is a main ingredient in soil. Bedrock is the solid layer of rock beneath

the soil. When bedrock is exposed to the surface,

it slowly weathers away into smaller particles of soil.

Soil isn’t just rock Soil is a mixture of rock particles,

minerals, decayed organic material, water, and air.

Sand, silt, and clay make up the portion of soil that comes from weathered rock.

So where did the organic material come from?

The decayed organic material is called humus. This is formed when plant and animal remains decay and break down in soil. It is dark colored.

Humus allows for spaces in soil for air and water for plants

Nutrients such as nitrogen, sulfur, phosphorus, and potassium are also found.

Fertile soil is soil rich in nutrients. Plants need nutrients in order to grow. Fertility of soil measures how well soil

supports plant growth. Soil with lots of humus has high fertility

Would sandy soil with little humus be good for growing plants?

Soil Texture

Soil texture depends on the size of the soil particles› Ex: sand is coarse and grainy, clay is

smooth and silky Soil is classified by size

› Clay, silt, sand, gravel Depending on the textured, depends

on what types of plants can grow

Loam is the best type of soil for plants

Equal parts clay, sand, and silt

Allows for both air and water

Process of Soil Formation

Soil forms as rock is broken down by weathering and mixes with other materials on the surface

Soil is constantly being formed wherever bedrock is exposed.

Soil is broken up into layers called horizons.

3 different horizons Topsoil: horizon A, crumbly dark brown,

mixture of humus, clay and other minerals

Subsoil: horizon B, clay and other particles washed down from horizon A, little amount of humus

Horizon C: partially weathered rock

Soil types Scientists classify the different parts of

soil into major groups based on climate, plants, and soil composition.

Open text page 251

Living Organisms in Soil

Soil contains all kinds of living things. Some soil is made from living

organisms. They help make humus, which makes the soil fertile.

Other organisms allow for air and water to mix in.

When plants leaves fall off they create litter. This is a loose layer on top of soil.

http://www.youtube.com/watch?v=Y1B1FtHL10k

http://www.brainpop.com/science/earthsystem/soil/

Humus is formed in a process called decomposition.

Organisms that live in the soil break down this dead organic material into humus.

Fungi, bacteria, worms, and other organisms are decomposers.

Worms, burrowing animals like mice and gophers mix the soil and add nitrogen from their waste and aerate it to add oxygen.

Chapter 8 section 1Weathering

http://www.youtube.com/watch?v=Xdg1lpQfLbo(Bill Nye Erosion)

What is the first step before we get soil? Weathering…

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

When rock is exposed to the surface, it faces weathering

Ice, heat, cold, water, elements in the atmosphere, all contribute to weathering.

So isn’t that erosion?

Erosion is the process by which the weathered pieces of rock are carried away by forces such as wind, water, ice, and gravity.

Weathering and Erosion work together to wear down and carry away rocks at the Earth’s surface.

2 types of Weathering

Mechanical and Chemical

Mechanical Weathering is caused by a force PHYSICALLY breaking down a rock› Ex: freezing and

thawing, release of pressure, animal actions, plant growth, abrasion (grinding of rock by wind, water, ice, and gravity)

Chemical Weathering

Chemical weathering “attacks” a rock, it breaks it down through chemical changes.

What is a chemical change? Actions of water, oxygen, carbon

dioxide, living organisms, and acid rain all chemically change a rock.

New minerals can be produced: feldspar=clay

Holes or soft spots are created and helps break apart the rock

Mechanical and chemical weathering work together.

Types of Chemical Weathering

Water: most important; dissolved rock, can create solutions

Oxygen: oxidation-when iron combines with O2 it becomes rust

Carbon Dioxide: dissolves in rainwater and creates carbonic acid and weathers marble and limestone

Living organisms: roots of plants produce weak acids that weather rock

Acid Rain

Acid Rain: burning of fossil fuels pollute the air with sulfur, carbon, and nitrogen compounds. They react with water vapor in clouds and make weak acids that fall down as rain.

Chp 9- Erosion

Remember that erosion is the process by which natural forces move weathered rock from one place to another.

What is sediment? Sediment is material moved by erosion,

contains living and non-living material Deposition occurs when after erosion,

sediment is left behind or deposited in a new location; helps change shape of land

Erosion in many places

Erosion occurs through gravity, water, glaciers, waves, and wind.

Gravity helps in pulling rock and other materials down hill. This process can be slow or fast.

Water Erosion Moving water is a major attributor of

erosion that helps change the Earth’s surface.

Runoff is a process that moves water over Earth’s surface.

Rivers help create valleys, waterfalls, flood plains, and lakes

Caves can also form erosion underground.

Glaciers

As glaciers ( a large mass of ice) move over land, they can move earth with it.

Waves

Energy in waves comes from wind that blows across the Earth’s surface.

This causes the water to move up and down.

Waves shape the coast through erosion by breaking down rock and transporting sand and other sediment.

As waves deposit sediment, they create beaches.

https://www.youtube.com/watch?v=pxmHHoTPSKI (sand)

Wind

Wind causes erosion by deflation and abrasion.

As wind blows along the surface, deflation occurs by moving surface materials.

Abrasion occurs when sand in the wind can polish a rock.

Wind then deposits sediments in areas where they can build up.

http://www.youtube.com/watch?v=gx2wVHeiTKE