Weathering and Soil Rocks and Weathering Uniformitarianism - The same geologic processes that work today worked in the past to change Earth’s surface What.

Weathering and SoilRocks and Weathering

Uniformitarianism - The same geologic processes that work today worked in the past to change Earth’s surface

What are these processes? Erosion- breaking of rocks into smaller pieces and removal of those rocks

and pieces by wind, water, ice or gravity.

Weathering-Chemical and physical processes that break down rock and other substances, heat, cold, water, ice and gases contribute

Weathering and SoilTwo Types of Weathering1.) Mechanical-rock is physically broken down into smaller pieces

--usually works slowly --over long periods of time, can wear down mountains

Freeze thaw- important in cold climates, H2O seeps into cracks in rocks, freezes and expands which forces the rock apart this is called FROST WEDGING

Release of pressure-erosions removes material from surface of a mass of rock, pressure on rock is reduced which causes the outside of the rock to crack and flake off

Plant growth-roots enter cracks of rocks, as plant grows, so will roots causing cracks to get larger

Action of animals-burrowing by moles. Gophers, prairie dogs and insects loosens soil and breaks apart rocks

Abrasion-the grinding away of rock by other rock particles carried in water, ice or wind

Weathering and Soil2.) Chemical- process that breaks down rock through chemical processes--process works with mechanical weather

--creates holes or soft spots in rocks

--rock breaks into pieces creating larger surface area for chemical weathering to work

Water-dissolves rock and carries other substances that break down rock, ie O, CO2 and other substances

Oxygen- combines with Iron to form rust, this is called oxidation

--rust makes rocks soft and crumbly and causes red/brown color

Carbon dioxide- when dissolved in water forms carbonic acid which easily weathers some rocks like marble and limestone

Living organisms-plant roots produce weak acid that breaks down rock, ie. lichens

Acid rain-burning of fossil fuels puts S, C and N in the air. These compounds react with water vapor, rain produced is more acidic than normal = acid rain.

--Acid rain rapidly causes chemical weathering

White lichens cover a blue granite gravestone like snow near Lake Champlain, New York. Lichens,

symbiotic organisms that combine fungi and algae, can be powerful weathering agents, secreting

chemicals called chelates that work to break down rock.

The effects of acid rain can be seen on this close up of this statues face. The acid rain has reacted with the mineral grain of the rock which has over time caused cavities to form as well wearing away the definition of the facial features.

Weathering and SoilRate of weathering depends on two thing

1.) Type of rock-minerals determine how fast the rock weathers

Minerals that dissolve easily = fast weathering

Porosity- a measure of how much of a rock is open space

Permeable- characteristic of material that contains connected air spaces or pores, that water can easily seep through

-spaces increase surface area of rock allowing weathering to occur more quickly

2.) Climate

Wet climate = increase physical and chemical weathering

High Temperature = increase chemical weathering

**chemical reactions occur more quickly at high temperatures

Human activities also can increase the rate of chemical weathering

-more people in an area = more pollution = more acid rain (chemical weathering)

Weathering and Surface AreaWeathering breaks rock into smaller pieces. While the pieces are usually irregularly shaped, you can model the process with cubes. The diagram shows what would happen if a rock cube broke into smaller cubes.

Weathering and SoilHow Soil Forms

Soil-the loos weathered material at Earth’s surface in which plants can grow

-mixture of rock, minerals., decayed organic material, water and air

-forms constantly wherever bedrock weathers, continues over a long period of time.

Composition

Bedrock-solid layer of rock beneath soil

-exposed to air, H2O and living things it weathers

Soil Particle Size-gravel, sand, silt, clay = portion of soil from weathered rock

Humus-dark colored, organic material in soil

-creates spaces in soil for air and water, contains nutrients plants need

Fertility

Fertitility- a measure of how well soil supports plant growth

-rich in humus = high fertility

-sandy soil = low fertility (low humus)

Weathering and SoilSoil Texture depends on particle size

Sandy soil = course, grainy Soil with lots of clay = smooth and silky

important for plant growth Mostly clay holds a lot of water and little

air = plant death Sandy soil = loses water quickly = plant death

Loam- rich fertile soil that is made up of

equal parts clay, sand and silt Best for growing MOST plants

Soil pH

pH less than 4 = acidic, reacts with some metals, turns blue litmus paper red

pH greater than 10 is strongly basic, feels slippery turn red litmus paper red

pH of 7 = neither acidic or basic, ie. water

Soil can be acidic (most acidic = 4) or basic, garden plants like pH 6-7.5

Weathering and SoilSoil FormationRock is broken down by weathering and mixes with other materials on surface--- soil is formed

Soil Horizon

Horizon A-

Topsoil- dark, crumbly, mixture

of clay, humus, and minerals formed from plants adding organic material and plant roots weather rock

Horizon B-

Subsoil-clay,

particles of rock, little

humus Rain water washes

materials down

from horizon A

Horizon C- small

particles of

weathered bedrock

Weathering and SoilSoils of North America Soil, fertility, and climate affect the types and numbers of plants that grow in a region.

Weathering and SoilHow Do Living Things Affect Soil Organisms make humus Mix soil to make space

for air and water

Forming Humus Organic remains = dead

leaves, roots, and plant

materials Formed from decomposition

Decomposers-

Mixing Soil Burrowing mixes humus with air and materials in soil Animal waste

contributes to nutrients

in soil

From Rock to Soil The illustrations show a rock and rich, fertile soil. What are the three processes that could change rock into soil?

Weathering and SoilSoil Conservation

Natural resource- anything naturally occurring in the environment that people use

Soil = one of Earth’s most valuable resources everything that lives on land depends directly or indirectly

on soil 1/8 of land on Earth’s land is farmable Soil takes a long time to form, few cm in hundreds

of years

Soil damage and Loss

Loss of Fertility Loss of moisture and nutrients– can occur when only one crop is grown Desertification- the advance of desert like conditions into areas that previously were fertile

Loss of Topsoil Exposure to wind and water causes erosion Plant covering can protect

Break force of falling rain Hold soil together

Sod- the thick mass of tough roots at the surface of the soil, holds soil in place

Weathering and Soil Soil ConservationThree ways people use land that might cause changes

1.) farming

2.) mining

3.) development- construction of homes, roads and other structures

Soil Conservation-the management of soil to minimize its destruction

Crop rotation-the planting of different crops in a field each year; corn or cotton one year followed by oats, barley or rye Corn, cotton take up large amounts of nutrients Peanuts, alfalfa and beans restore nutrients Legumes contain pods of nitrogen fixing bacteria

Contour plowing-fields plowed along curves of a

slope instead of straight rows Slows runoff, prevents soil from washing away

Conservation plowing-dead weeds and stalks

are plowed into the ground Returns nutrients to soil, retains moisture and hold soil in place

Weathering and SoilDust BowlParts of Oklahoma and surrounding states that lost soil is the 1930’s were called the DUST BOWL

Farmers plowed the land removing the sod and exposed soil, drought dried out the topsoil which turned to dust and blew away = Desertification

Land Reclamation- the process of restoring an area of land to a more natural, productive state