Subsurface refers to the layer of soil, rock, or other materials located beneath the Earth's surface. This area is crucial for various natural processes, including water filtration, nutrient cycling, and the growth of plant roots. Understanding subsurface conditions is essential for fields like geology, agriculture, and environmental science. In construction and engineering, subsurface investigations help determine the stability and suitability of land for building projects. Techniques such as drilling and soil sampling are used to assess the subsurface composition. Knowledge of the subsurface is vital for managing resources like groundwater and for mitigating risks related to landslides or earthquakes.