How do scientists organize soil ? How is composition of soil affected by the climate? What important benefits does soil provide? How does chemical weathering differ from mechanical weathering?
1 Answer
Generally, they are either sands or clays.
Explanation:
Soils may be classified differently for engineering purposes (most common references) than for environmental or earth science categories.
For this context I will use the earth science designations. The reference and further information is here:
http://environment.uwe.ac.uk/geocal/SoilMech/classification/default.htm
The majority of soils may be regarded as either SANDS or CLAYS:
SANDS include gravelly sands and gravel-sands. Sand grains are generally broken rock particles that have been formed by physical weathering, or they are the resistant components of rocks broken down by chemical weathering. Sand grains generally have a rotund shape.
CLAYS include silty clays and clay-silts; there are few pure silts (e.g. areas formed by windblown Löess). Clay grains are usually the product of chemical weathering or rocks and soils. Clay particles have a flaky shape.
All soils originate, directly or indirectly, from solid rocks in the Earth's crust:
igneous rocks from crystalline bodies of cooled magma
e.g. granite, basalt, dolerite, gabbro, syenite, porphyry
sedimentary rocks are layers of consolidated and cemented sediments, mostly formed in bodies of water (seas, lakes, etc.)
e.g. limestone, sandstones, mudstone, shale, conglomerate
metamorphic rocks are formed by the alteration of existing rocks due to heat from igneous intrusions (e.g. marble, quartzite, hornfels) or pressure due to crustal movement (e.g. slate, schist, gneiss).
Soil is necessary to support plant growth, which is the basis of the entire land-based food chain.
Climate affects soils with respect to weathering or possible transport and the organic life it can support. The composition is dependent upon the base rock material and organic material. Thus, deserts will have different soil from temperate or tropical forests.
Chemical weathering is the result of chemical reactions that change the fundamental material. An example would be acid rain. Mechanical weathering is any physical breakdown of the base material by contact with other materials such as sand particles or water ice. No changes of composition occur.
