chemical weathering, but always involve a living organism. Soil is usually composed of 45%
mineral particles, 25% air, 25% water, and 5% organic matter.
Mechanical weathering can happen through water, and wind. Water erosion happens most when
vegetation isn’t prevalent. For example, in areas where the soil isn’t anchored by trees or plant
life, soil erosion can happen very easily. The same usually happens with wind, when there are
little buffers and anchors holding the soil down, wind can easily blow the top soil away.
Chemical weathering happens when water breaks down rock and certain minerals are
weathered away, changing the soil make-up. Chemical weathering is a result of chemical
reactions in the soil. Some minerals chemically react with water and causes the formation of
different types of soil. Biological weathering combines mechanical and chemical weathering, but
it is caused by living organisms. For example, when lichen grows on rock this promotes chemical
weathering. Soil is divided into horizons labeled O-R. The O horizon is the first layer of soil, the
leaf litter and fallen decomposed organic matter. The A horizon follows with the topsoil, this
contains humus, living organisms, and inorganic materials. The E comes third, and this is called
the zone of leaching. This is where dissolved or suspended materials move downwards. The B
horizon is known as the subsoil layer, this holds iron, aluminum, humic compounds, and clay
that leached down from the A and E horizons. The C horizon contains weathered parent material:
partially broken down inorganic materials. And last but not least the R horizon is the bedrock.
There are different characteristics of soil. Chemical features of soils are pH, ion content,
and ion-holding capacity are determined by the physical characteristics of the soil. Chemical
factors in soil are very important when it comes to plant life. Some plants prefer slightly acid or
basic soil. For example, in tropical rainforests the soil is slightly acidic. Although there aren’t a
lot of smaller plants that grow directly on the soil, the trees thrive in this environment and offer a