4.2 Soil Formation and Erosion

Describe soil.

is a combination of geologic and organic material that forms dynamic membrane of surface on earth

Describe when weathering occurs.

occurs when rock is exposed to air, water, certain chem compounds (degrades rocks)

Define physical weathering.

mechanical breakdown of rocks and minerals

Describe two ways of physical weathering

1. Water can go through the cracks in rocks and remove loose material and widen cracks with water freezes

2. A difference in temperature can cause rock to expand and contract

3. Plant roots can grow and crack rocks

Define chemical weathering.

breakdown of rocks and minerals by chemical reactions and dissolving rocks

Describe why physical weathering increases the rate of chemical weathering.

physical weathering increase chemical weathering by breaking down large rocks into smaller rocks which exposes greater surface area which allows more chemical reactions

Describe how the chemical weathering of feldspar aids in plant growth.

when feldspar is exposed to natural acids in rain it forms clay particles and release ions

Explain how carbon dioxide can lead to chemical weathering

carbon dioxide dissolves in water vapor to create weak acid and when water contains carbonic acid flow, they dissolve rocks

Define acid precipitation (acid rain)

precipitation high in sulfuric acids and nitric acid from reactions between water vapor and sulfur and nitrogen oxides

Explain how knowing rates of weathering can assist researchers

knowing weathering rates helps researchers predict climate change impacts and manage soil formations

Define erosion

physical removal of rock fragments from landscape/ecosystem

Describe the two mechanisms of erosion

1. wind, water, and ice more soil and other materials by downslope creep under force of gravity

2. living organisms like animals that burrows under soil

Describe deposition

accumulation/ depositing of eroded materials (sediment, rock fragments, or soil)

List the functions of soil

1. filters water

2. habitat for variety of organisms

3. breaks down organic material and recycles nutrients

4. medium for plant growth

Describe what happens to the depth of soil through time.

the depth of soil typically increases over time

Define parent material

is the underlying rock material from which its inorganic components are derived

Describe the differences between a parent material that is nutrient poor and one that is nutrient rich

parent material that is nutrient poor will make quartz. A soil that has high nutrients will contain abundant supply of calcium, high pH, and support high agricultural productivity

Explain how climate influences soil formation

Long term accumulation of temp, humidity, and water affect soil development

soils do not develop when temp are below freezing because decomposition of organic matter and water movement are very low in frozen soils

soils at high latitudes of the northern hemisphere are composed of organic material

soil develop in more humid areas in sped up by rapid weathering of rocks and soil minerals

climate affects the type of vegetation that develops

Describe topography

the surface slope and arrangement of a landscape. soils that form on steep slopes are subjected to erosion and more drastic mass movements of material. soils that form at the bottom of steep slopes may accumulate material from higher elevations

Define soil degradation

the loss of some or all of the ability of soils to support plant growth

Describe the major causes of soil degradation

1. soil erosion, occurs when top soil is disturbed (vegetation is removed)

2. soil by machines, humans, and livestock can reduce soils ability to retain moisture

3. compaction and drying of soil can lead to reduced vegetation and increase erosion

Describe the time it takes for soil to develop

Soils in places like the grasslands support much of the food crop and livestock because it has had continual inputs of organic matter for a lot of years

other soils that are equally old but with less productive communities and greater amount of water moving through can lead to infertile soil

Define horizon

horizontal layers with distinct physical features (color/texture)

Define O horizon

at the surface of many soils

composed of organic detritus like leaves, needles, twigs, and animal bodies

contains humus

Define humus

the most fully decomposed organic matter in the lowest layer of O horizon

Define A horizon (topsoil)

top layer of the soil, a zone of organic material and minerals that have been mixed together, including humus

most biological activity and decomposition occurs

most fertile soil

Define E horizon

a zone of leaching found under 0 horizon or less often the A horizon

when E horizon is present, it always occurs above B horizon

Define B horizon

known as subsoil, composed primarily of mineral material with very little organic matter

zone of accumulation

rich in inorganic metals (iron, aluminum, sand, silt, clay)

Define C horizon

least-weathered soil horizon, always occurs beneath B horizon and similar to parent material

 Identify what soil horizon composition depends on

climate, organisms, parent material, and time