Ch 21

Section 1

Weathering and Soil

Weathering   The process of physical or chemical breakdown of

material at or near Earth’s surface.   Interaction of water, air and rock over time.

  Factors that influence weathering:   Water   Air

  Nature of material being weathered   Climate   Time

Mechanical weathering   Changing big material into small material.

  Forces that cause mechanical weathering are expansion or contraction of materials and biological effects.

Prying Rock apart   When water freezes it expands. If water freezes

while in rock it will force the rock apart and spit it.   Frost weathering

  As rocks fall off cliffs they can impact other rocks and break them apart.   Impact agents

Chemical weathering   Process of chemicals interacting with material then

forming new material during a chemical reaction.   Water and oxygen are the key components to

chemical weathering.

Soil   mixture of weathered rock, organic matter, water,

and air that is capable of supporting plant life.

  Soil is the end product of weathering.

  O and A layers are considered top soil. (where plants get most of their nutrients)

  E- where finer sediments and soluble materials settle down.

  B- collects the materials from above and is usually darker than the upper layers.

  C- partially crumbled and weathered bedrock.

  R- unweathered bedrock.

Soil types   Soil is separated according to composition and

physical properties.   Amount of precipitation   Temperature range   Vegetation present

Soil conservation   Soil depletion can occur when over planting takes

place.   Plants use up nutrients from soil and when farmers

don’t replenish the nutrients the soil will become useless.

  Farmers can correct the soil depletion by adding fertilizers.

  Soil erosion can take place if the vegetation is removed or because the land is too steep.   Deforestation or soil on a hill.