Regolith (pronounced re-go-lith) is a layer of loose, heterogeneous material covering solid rock. Regolith is present on Earth, the Moon, some asteroids, and other planets. The causes of regolith on Earth are erosion, weathering, and biological processes. On Earth, regolith is mainly composed of sedimentary rock. On bodies without an atmosphere, regolith is caused by the gravitational reaggregation of debris resulting from impact with other objects.

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.

On the Moon, regolith has been formed by the action of micro-meteroids breaking down surface rocks into a powder. This powder is more reflective than the basalt that makes up the lunar maria, and therefore looks brighter when viewed from Earth. There were (apparently) concerns before the landing of Apollo 11 that the regolith would not be supportive enough to cope with the weight of the lunar module and that the module would begin to sink beneath the surface.

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