Soil is formed through the decomposition of organic matter and rocks, weathering and erosion, and is made up of minerals, organic matter, water, and air. It exists in layers called horizons or profiles and can be sandy, clay, or loam soil depending on particle size, each with different abilities to retain air and water that plants need. Loam soil, with a mix of particle sizes, provides the best environment for plant growth by allowing both air and water in the soil.