Technically, soil forms the pedosphere:
the interface between the lithosphere (rocky
part of the planet) and the biosphere, atmosphere, and hydrosphere. More
generally, soil is a three phase system comprised of various combinations of
naturally- derived solids including fine to coarse-grained rocks and minerals,
organic matter, ice, weathered rock and precipitates, liquids primarily water
solutions, and gases. The liquid phase is typically primarily water, and is also
known as the 'soil solution'; plants take their nutrients from this phase. The gaseous
phase is important for supplying oxygen to plant roots for respiration. Soil
formation, or pedogenesis, is the combined effect of physical, chemical, biological,
and anthropogenic processes on soil parent material resulting in the formation of
soil horizons. Dependence on and curiosity about soil, exploring the diversity and
dynamic of this resource continues to yield fresh discoveries and insights. New
avenues of soil research are compelled by our need to understand soil in the
context of climate change, greenhouse gases, and carbon sequestration. Our
interest in maintaining the planet's biodiversity and in exploring past cultures has
also stimulated renewed interest in achieving a more refined understanding of soil.
