Virtually every soil "lives" in that all of its properties undergo changes with time - some insignificant, but others very important. Time-dependent chemical, geomicrobiological, and mechanical processes may result in compositional and structural changes that lead to softening, stiffening, strength loss, strength gain, or altered conductivity properties. The need to predict what the properties and behavior will be months to hundreds or thousands of years from now based on what we know today is a major challenge in geoengineering.