4.2 -3 Soil Formation & Composition

APES

rock

a mixture of minerals that have been under similar
conditions

rock cycle

the constant formation and destruction of rock.

igneous rock

rock that form directly from magma.

intrusive igneous

form from within Earth as magma
cools.

extrusive igneous

from when magma cools above
Earth.

sedimentary rock

form when sediment such as mud,
sands, or gravels are compressed by overlying sediment.

metamorphic rock

form when sedimentary, igneous or
other metamorphic rocks are subjected to high
temperatures and pressures.

physical weathering

the mechanical breakdown of
rocks and minerals

Abrasion

caused by wind or
water flowing over rocks

exfoliation

caused by changes in pressure

root pry

caused by roots growing on or aroound rocks

frost wedging

caused when water freezes between cracks in rock and breaks the rock

chemical weathering

the breakdown of rocks and minerals by chemical reactions

hydrolysis

breakdown by water reacting
with silicate based rocks

carbonation

atmospheric carbon dioxide
is dissolved in rain creating carbonic acid
breaking down limestone

oxidation

oxygen and water combine with a
metal resulting in it breaking down, most
common with iron statues

plant or animal acids

acids excreted by animals or plants, such as lichens, break down rocks

erosion

the removal of rock

deposition

the accumulation or depositing of eroded material such as sediment, rock fragments or soil

soil is important because it (4)5 f

Is a medium for plant
growth
• Serves as a filter for water
• A habitat for living
organisms
• Breaks down organic
material and recycles
nutrients.

5 factors of soil formation

parent material, topography, climate, time, organisms

O horizon

composed of the leaves, needles, twigs and
animal bodies on the surface.

A horizon

the zone of organic material and minerals mixed together.

B horizon

composed primarily of mineral material with very
little organic matter

C-horizon

the least weathered horizon and is similar to the
parent material

4 components of soil

Mineral Matter, or broken-down rock
• Humus - the decayed remains of organisms
• Water
• Air

physical properties

texture- sand, silt, clay

permeability- how quickly soil drains, depends on texture

chemical properties

cation exchange capacity, soil bases/acids, base saturation (look at notes)

biological properties

Many organisms are found in the soil including
fungi, bacteria, protozoa, rodents and earthworms.