dirt

Dirt is a common term for soil or earth that is out of place or stained, rather than the natural soil in which plants grow. In scientific usage, soil is the natural body found in the upper layer of the Earth's crust, composed of mineral particles, organic matter, water, and air, capable of supporting plant life. Dirt is thus often considered soil that has been removed from its context or rendered dirty.

Soil is largely determined by its mineral fraction, which is described by particle size: sand, silt, and clay. The relative proportions create textures such as sandy, clay, loam, or silt loam, influencing properties like water retention, drainage, and nutrient holding capacity. Organic matter from decaying plants and animals adds nutrients, improves structure, and fosters biological activity. The space between particles forms pores that hold water and provide aeration, while color reflects mineral content and humus.

Soil forms through weathering of rocks, accumulation of organic material, climate, topography, organisms, and time. It supports plant growth, acts as a habitat for countless organisms, and serves as a filter and reservoir in hydrological cycles. In human use, dirt has applications in agriculture, construction (as fill or subsoil), and recreation, but erosion, contamination, or compaction can degrade soil quality and ecosystem services.

Exposure to airborne dirt or dust can pose health risks, especially for fine particulates such as silica dust. Cleaning and removal should minimize generation of dust, and protective equipment may be required in occupational settings.