Soils can also be considered to be energy transformers in that they are physical structures of material that are modified by naturally occurring processes. The sun constitutes the primary energy source for soils, and significantly outweighs any heat generated by radioactive decay flowing up from deep within the Earth's crust. The deposition of sediment, or the addition of groundwater or rain, can also be considered an energy gain because new minerals and water can alter preexisting materials within the soil. These processes, coupled with the amount of energy available to fuel them, are what create a soil profile.