Chemical weathering but always involve a living

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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
diverse environment for more plants and animals. Soil texture is determined the percentage of silt, sand, and clay. Usually when determining soil texture, a soil chart is used. Soil texture is important, because it impacts the amount of water the soil can hold, the rate of water movement into the soil, and how fertile the soil is. The amount of water soil can hold is called water availability, the rate at which water moves through the soil is called infiltration, and the measurement of how fertile the soil is is called fertility rate. All of these characteristics are present in soil. Clay, for example, has a diameter of <0.002 mm (clay has the smallest diameter out of the 3 soil groups), is the most dense (this causes the soil to be very very thick, this makes it harder for roots to penetrate and for plant life to grow), the density makes this type of soil less susceptible to erosion and weathering, also soil has very little nutritional value, since it contains little organic matter.

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