Soil is the loose material of the earth’s surface in which the terrestrial plants grow. It is usually form from weathered rock or regolith changed by chemical, physical and biological process.
- The early phase of soil formation starts by disintegrating the rock under the influence of climate.
- Rainwater will dissolve rock elements, temperature fluctuations will cause cracks and fissures in the rocks.
- Freezing and thawing of water captured in the rock will widen existing cracks and cavities.
- Pioneer vegetation, at first lichens, will settle and their roots will further loosen the rock.
- Moreover, decaying plant debris will produce organic acids, which further disintegrates the rock.
- Organic matter will start to accumulate and be mixed with the mineral material provided by the rock.
- Over time, rock minerals will be dissolved or transformed.
- Elements release from the rock will precipitate and new minerals may be form. For example, iron will be oxidize and precipitate as iron oxides or hydroxides, giving the soil reddish or yellowish-brownish colours.
- Soil fauna will settle and mix (‘homogenize’) the soil. The soil will grow in depth through newly formed soil material at the bottom.
- The soil matures.
- Given sufficient time under stable environmental conditions, soils will reach a steady state, whereby soil build-up matches their breakdown.
- Production of humus from decaying vegetation debris will equal its consumption by soil microbae, fauna and flora.
- Transformation of rock minerals into soil minerals will keep pace with the removal of earlier formed soil minerals.
- Slow surface wash of topsoil is match by new formation of soil material from the bedrock.
- The soil has aged.
Rock To Soil Formation
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