Rock at or near the surface is slowly attacked by the
atmosphere, by groundwater, and by organism. The rock is broken down physically
and altered chemically. Soil is the most important product of this weathering,
and particles of rock are set loose for gravity to act upon them.
Weathering is divided into two types:
physical or mechanical weathering (disintegration) and chemical weathering ( decomposition
) These takes place together, but usually one is more prominent than the other,
depending on the climate and the kind of rock.
Air is composed of nitrogen, oxygen,
argon and other essential gases, plus varying amount of carbon dioxide and
moisture.
Differential weathering is the diverse
effect of weathering on rock. It acts differently on various natural cements
that hold sedimentary rocks together, as well as on unlike part of the solid
bodies themselves. Various areas of a rock may weather to different degrees,
often producing a hollowed or patchy effect.
Soil is mixture of broken rock,
decomposed rock, and decaying plant matter called humus.
Soil helps to prevent erosion by controlling drainage. The
effect of gravity acting on loosened rock may produce a number of kinds of down
slope movement also called mass
wasting. Even solid rock moves slowly but inevitably under the influence of
gravity.
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