Soil

The First Doctor observed that the soil on Skaro following the Neutronic war was barren, having been turned to sand and ashes. However, shrubs and trees remained as part of the petrified jungle. Temmosus of the Thals wished to make the soil live again with the Daleks' help. After the Daleks were destroyed, the Doctor made tests on the soil, leading him to indicate to the Thals that it was not quite so barren as they thought. (TV: The Daleks)