Clone feed was similar to amniotic fluid, but for Sontaran clones. The Sontarans intended to use the ATMOS to fill the atmosphere of the planet Sol 3 with poisonous gas, which would become fuel for their new clones, and Earth would have become a clone world. However, the Tenth Doctor thwarted their plans by clearing the atmosphere. (TV: The Sontaran Stratagem/The Poison Sky)