Chapter 8 Weathering & Soil Formation

WEATHERING A process that breaks down rock & other substances. (Hammer-rock) Heat, cold, water, ice, oxygen, & carbon dioxide all contribute to weathering.

Weathering Examples Repeated Freezing/Thawing Rainwater dissolves minerals that glue rocks together. Wearing down of rock, mountains, bikes rusting, sidewalks cracking, potholes on the road.

What does Weathering do? breaks rocks apart.

Erosion The carrying away of rock particles by wind, water, ice, or gravity.

Weathering & Erosion Both work together to break apart rock & carry it away. This shaped Earth’s surface millions of years ago.

Principle that states that the same processes Uniformitarianism Principle that states that the same processes (weathering/erosion) that operate TODAY operated in the PAST.

TYPES OF WEATHERING 2. Chemical Weathering 1. Mechanical Weathering Rock is physically broken apart. Like a hammer smashing a rock. Slow process. 2. Chemical Weathering • Breaking down rock through chemical changes.

Mechanical Weathering Examples Freezing/Thawing Plant growth Actions of animals Abrasion

Freezing/Thawing Water seeps into cracks in rocks & freezes when the temp. drops. As water freezes, it expands & cracks the rock (ice wedge). As the process continues, water goes deeper & cracks get bigger & it breaks apart.

Plant Growth Roots of plants & trees get in cracks of rocks and as the roots grow, they make the cracks bigger & the rock breaks apart.

Abrasion Sand and other rock particles carried by wind, water, & ice wear away rock. It hits the surface of the rock & wears it down (rubs against and wears it down).

Abrasion

Types of Chemical Weathering Water- Creates holes or soft spots in the rock & dissolves the rock. Oxygen- rocks that contain iron will rust.

Chemical Weathering Carbon Dioxide- dissolves in water and gets into the soil to create carbonic acid which decays rocks. Living Organisms- plants grow on rocks & release weak acids. Acid Rain- mixture of pollutants in rain that decays rock.

2. climate- weathering occurs faster in wet climates. Rate of Weathering Depends on: 1. the type of rock (rocks that don’t dissolve in water weather slowly) dissolve= faster rate. 2. climate- weathering occurs faster in wet climates.

Section 2 Soil Formation

SOIL The loose, weathered material on the Earth’s surface in which plants can grow. Soil comes from bedrock.

Bedrock The solid layer of rock beneath the soil. Once exposed at the surface, bedrock gradually weathers into smaller pieces that make up the soil.

Soil Makeup Soil is mixture of rock particles, minerals, decayed organic matter, water, & air. Sand, silt, clay make up the portion of soil that comes from weathered rock.

Dark-colored soil that forms from decayed plant & animal matter. Creates spaces in the soil for air & water. Provides important nutrients (nitrogen, sulfur, potassium) for the plants. FERTILE SOIL.

Fertility of Soil Is a measure of how well the soil supports plant growth. Soil that is lots of humus has HIGH fertility. Sandy soil is low in humus & has LOW fertility.

Classification of Soil Particles Soil is classified by the size of the soil particles. Gravel- largest Clay- smallest(.)

Soil Texture Depends on the size of the soil particles. Sand- feels coarse/grainy, Clay feels smooth/silky dense. Texture is important for plant growth. Clay soil can hold lots of water so plants can drown in it (lack of air). Sand-water runs through it quickly so plants can dry out fast in sandy soil.

Soil Texture Soil made up of equal parts of clay, sand, & silt (LOAM) is best for growing plants. It holds both air & water.

SOIL FORMATION Rock is broken down by weathering & mixes with other materials on the surface to create soil.

Soil Horizons A layer of soil that differs in color & texture from layers above or below it. A Horizon- topsoil B Horizon- subsoil C Horizon- bedrock

A Horizon A Horizon- is made up of topsoil- a dark brown soil that is a mixture of humus, clay, and other minerals. Layer develops as plants add organic matter to the soil & plant roots weather pieces of rock.

Horizon B- subsoil- clay & other particles that get washed down by rain water from Horizon A. (little humus) Horizon C- weathered rock that breaks up in the soil. (plant roots)

Rate At Which Soil Forms Depends on the climate & type of rock. Hot/wet climates= fast. Cold/dry climates (weathering slow)= slow formation of soil.

Classification of Soil Based on climate, plants, & soil composition. PA- Northern forest soils- cool, wet climates, soil ranges from thick/fertile to thin with little humus. Most fertile soil- areas with moderate temps & rainfall. Midwest US. (Prairie Soils).

Role of Living Organisms in Soil 1. Some living things make humus (with remains or wastes) 2. others mix the soil around creating space for air & water.

ROLE OF LIVING THINGS IN SOIL Plants contribute the most humus. They shed leaves that form a litter & when they die, their remains fall into the ground & decay. Humus forms from this process of decomposition. Decomposers break the remains into smaller pieces & digest them.

Decomposers Decomposers- organisms that live in the soil & turn dead material into humus. (eat it) Fungi (mold, mushrooms), bacteria, worms Fungi & Bacteria feed on plant remains. Worms decompose material & mix it into the soil.

Soil Mixers Earthworms do most of the mixing of humus & other materials in the soil. They eat through the soil & carry the humus down to the subsoil & pass out this as waste which enriches the soil to help plants grow. They also take it from the subsoil to the surface and create air pockets in the soil.

Soil Mixers Mice, prairie dogs, gophers burrow through the soil and break up hard soil, mix around humus throughout, & create air pockets in the soil.

8-3 Soil Conservation

SOD A thick mass of tough roots at the surface of the soil. Sod keeps soil in place & holds moisture.

VALUE OF SOIL Soil is a Natural Resource. Natural Resource- anything made by Earth that is used by people. (Soil, water, trees, coal) Most valuable natural resource because everything that lives on land depends on the soil. Plants need soil to live & grow. Animals/Humans need plants or other animals that eat plants for food.

Value of Soil It is also LIMITED. Only 1/8 of Earth’s land is suitable for farming. Takes a LONG TIME to form- 100’s yrs = 2/3cm.

2 Ways Topsoil Can Be Lost/Damaged Value of soil is reduced when: It loses it’s fertility When topsoil gets eroded. • Human activities & changes in the environment can cause soil damage.

1. Loss of Fertility Soil becomes exhausted when it loses all of it’s nutrients. 1800’s- cotton planted too much & soil lost all of nutrients. Land got depleted. Couldn’t farm on it. Must Crop Rotate- plant cotton one year (takes out N), next year plant peanuts or legume (puts N back into soil). Keeps fertile.

Whenever topsoil gets exposed, wind/water can take it away (EROSION). 2. Loss of Topsoil Whenever topsoil gets exposed, wind/water can take it away (EROSION).

DUST BOWL End of 1800’s many people started to farm in the Great Plains (MidWest US) because the soil was fertile. Droughts & plowing (which removed grass & exposed topsoil to erosion) caused the soil to dry out, turn to dust, & blow away. Farmland was ruined & winds blew the dry particles of soil into clouds of dust that traveled thousands of kilometers East (Chicago, NY).

DUST BOWL Helped make people appreciate & value the soil. People began to take better care of the soil. New methods were developed to conserve the soil.

Management of the soil to prevent it’s destruction. SOIL CONSERVATION Management of the soil to prevent it’s destruction.

SOIL CONSERVATION METODS Contour Plowing- plowing along the curves of the slope of the land. Prevents water runoff & soil from being washed away.

Farmers don’t disturb the soil. Conservation Plowing Farmers don’t disturb the soil. Weeds are not cut- let it there to help keep nutrients in the soil.

CROP ROTATION Keeps soil rich & full of nutrients. Planting different crops each year to prevent land depletion (lack of nutrients in the soil). Keeps soil rich & full of nutrients. EX: Year one plant cotton (takes N out of soil). Year two plant legumes or peanuts (puts N back into the soil).