Regolith - Earth

Earth

Earth's regolith comprises the following subdivisions and components:

• soil or pedolith
• alluvium and other transported cover, including that transported by aeolian, glacial, marine, and gravity flow processes.
• "saprolith'", generally divided into the
  • upper saprolite: completely oxidised bedrock
  • lower saprolite: chemically reduced partially weathered rocks
  • saprock: fractured bedrock with weathering restricted to fracture margins.
• volcanic ash and lavas
• duricrust, formed by cementation of soils, saprolith and transported material by clays, silicates, iron oxides and oxyhydroxides, carbonates and sulfates, as well as less common agents, into indurated layers resistant to weathering and erosion.
• groundwater- and water-deposited salts.
• biota and organic components derived from it.

Regolith can vary from being essentially absent to hundreds of metres in thickness. Its age can vary from instantaneous (for an ash fall or alluvium just deposited) to hundreds of millions of years old (regolith of Precambrian age occurs in parts of Australia).

Regolith on Earth originates from weathering and biological processes; if it contains a significant proportion of biological compounds it is more conventionally referred to as soil. People also call various types of earthly regolith by such names as dirt, dust, gravel, sand, and (when wet) mud.

On Earth, the presence of regolith is one of the important factors for most life, since few plants can grow on or within solid rock and animals would be unable to burrow or build shelter without loose material.

Regolith is also important to engineers constructing buildings, roads and other civil works. The mechanical properties of regolith vary considerably and need to be documented if the construction is to withstand the rigors of use.

Regolith may host many mineral deposits, for example mineral sands, calcrete uranium, and lateritic nickel deposits, among others. Elsewhere, understanding regolith properties, especially geochemical composition, is critical to geochemical and geophysical exploration for mineral deposits beneath it. The regolith is also an important source of construction material, including sand, gravel, crushed stone, lime, and gypsum.

The regolith is the zone through which aquifers are recharged and through which aquifer discharge occurs. Many aquifers, such as alluvial aquifers, occur entirely within regolith. The composition of the regolith can also strongly influence water composition through the presence of salts and acid-generating materials.