Topsoil is the uppermost layer of soil, typically ranging from about 2 to 12 inches (5 to 30 cm) deep, depending on the environment. It contains the highest concentration of organic matter, microorganisms, nutrients, and biological activity essential for plant growth

. This layer is composed of mineral particles (such as sand, silt, and clay) mixed with decomposed organic material (humus), which provides nutrients like potassium, phosphorus, and iron, and supports a rich microbiome including bacteria, fungi, insects, and worms. These organisms help break down organic matter, recycle nutrients, aerate the soil, and maintain soil health

. Topsoil is critical for plant life because it holds water and air, supplies nutrients, and supports root growth. It forms very slowly over centuries through weathering of rocks and accumulation of organic material, making it a finite and increasingly endangered resource

. In summary, topsoil is the vital nutrient-rich surface layer of soil that sustains most terrestrial plant life by providing water, nutrients, and a habitat for beneficial organisms