Rock to Regolith Conversion: Producing "User-Friendly" Material for Terrestrial Ecosystems

Weathering processes transform hard rock into friable weathered rock (paralithic material), which is the material that becomes soil and supports terrestrial life. The conversion of biologically inert hard rock to a “user-friendly” material for supporting organisms begins with the production of porosity. Porosity allows water to flow into and through the rock. It imparts a water-holding capacity to the rock so that water can be stored for prolonged use by organisms. Organisms themselves, in the form of microbes and plant roots, invade the rock as porosity forms. Porosity and mineralogical changes produced by weathering also make the rock vastly more chemically reactive by increasing its surface area and ion retention capabilities. In general, earth materials become progressively more user-friendly during the hard rock – paralithic material – soil transition; for example, water-holding capacity, hydraulic conductivity, penetrability, and cation exchange capacity all increase. However, some soils become less user-friendly at an advanced age; for example, when clay or other pedogenic materials plug pores and restrict water flow and root growth. Production of porosity is the fundamental process responsible for converting rock into a medium capable of supporting terrestrial ecosystems. Consequently, the rate of porosity formation during rock weathering is the ultimate measure of soil production and sustainability.