Entisols are soils, as defined under USDA soil taxonomy, that do not show any profile development other than an A-horizon (or “A” horizon). Entisols have no diagnostic horizons, and are unaltered from their parent material, which could be unconsolidated sediment, or rock. Entisols are the most common soils, occupying about 16% of the global ice-free land area.
Aquents – heavily saturated or soaked soils, mostly present at riparian locations (such as river banks, tidal mudflats, estuaries, etc). Here, consistent saturation limits development.
Fluvents – alluvial soils, where development is prevented by repeated deposition of sediment during periodic flooding events; present in valleysorriver deltas, especially those with high sediment load.
Orthents – shallow or "skeletal" soils; found at sites of recent erosion events, or very old landforms completely devoid of weatherable minerals.
Psamments – Entisols that are sandy (through all layers), and in which development is precluded by the impossibility of weathering the sand; formed from shifting or glacialsand dunes.
Wassents – Entisols that have a positive water potential at the soil surface for more than 21 hours of each day, in all years.
Most fossil soils, before the development of terrestrial vegetation in the Silurian, are entisols that show no distinct soil horizons. Entisols are common in the paleopedological record ever since the Silurian; however, unlike other soil orders (oxisol, ultisol, gelisol, etc) they do not have value as indicators of climate. Orthents may, in some cases, be indicative of an extremely ancient landscape with very little soil formation (i.e., Australia today).