Soil

Dirt is a colloquial term, often used synonymously with ground, earth, and soil.

It is the stuff that makes up a large proportion of the natural solid surface on earth, both emersed (above the water surface) and immersed (below the water surface); thought the term "dirt" is usually reserved for the former as once the water quantity within dirt is sufficient to allow it to take on a sticky to runny texture, it's referred to as "mud".

Dirt is a mix of inorganic particles derived from bedrock (mother material) which are categorized into three groups according to their size (from largest to smallest): sand, silt, and clay. The open spaces between particles are known as pores. These pores can - depending on environmental conditions - be filled with water, air (gases) or organic material (either dead of living) which can be micro- or macroscopic. A combination of these four elements (inorganic particles, organic material, air and water) is usually referred to as "soil". Soil is thus a living ecosystem in and of itself and an important factor in the health and sustainability of Earth's biome.

It comes in various colors, tints and tones like brown, yellow, orange, red, beige, grey and black.

The soil texture triangle, as used by the USDA.

Colors and Discerning Dirt

In some cultures, black dirt is seen as the most fertile. This is due to the high, microscopic organic content of the soil which oxidizes (known as humus), giving it a blackish colour.

Red dirt often has a high clay content and comes mainly from the oxydization of ferrous particles, while beige or yellow dirt often includes higher levels of sand.

Grey dirt with a very high clay content usually indicates poorly aerated, waterlogged soils and in that case is often accompanied by a foul smell akin to rotten eggs due to sulphur reducing bacteria thriving in anoxic conditions.

Growing in Dirt

When talking about dirt, most are referring to topsoil, which is a mix of earth, tiny organisms, and necessary nutrients and elements for growing plants. Dirt needs to include water, anchorage, oxygen, and nutrients, like phosphorus, nitrogen, and other substances.