Frontios' atmosphere was close to that of Earth - humans, Trions and Time Lords were able to breathe without special apparatus. The soil composition appeared to be mostly low-level scree and porous rocks. Beneath ground level, there was a vast network of tunnels excavated by the Tractators to create a gravity motor. Stone suitable for quarrying and building material was also available.
Frontos lay at the very periphery of the Time Lords' sphere of knowledge. It became home to a fledgling colony of human refugees in a ship captained by Captain Revere. They were among the last to leave Earth.
Frontios was not the original destination of the colony ship — it was pulled off-course by the Tractators (led by the Gravis) and crashed into the planet. The surviving crew and colonists were bombarded with meteors and randomly selected for enslavement in the Tractators' excavation machines.
After the removal of the Gravis, the Tractators became harmless, earth-burrowing creatures. No mention was made of their removal from the planet, so most likely they co-habited the planet with the human colonists. (TV: Frontios)