Fire

Fire was energy produced by oxidation.

The earliest splinter of Scaroth showed mankind how to make fire. (DW: City of Death)

By roughly 100,000 BC, fire had become a precious commodity, as relatively few humans knew how to recreate it once it was snuffed out; in some tribes this knowledge was held only by a select few. The Doctor and his companions Ian Chesterton, Barbara Wright and Susan Foreman encountered a tribe looking for this knowledge; Chesterton ultimately showed Za, a tribal leader whose predecessor was unable to give him the secret before dying, how to make fire. (DW: An Unearthly Child)

Incidents involving fire

 * The Doctor accidentally inspired Nero to start the Great Fire of Rome in 64. (DW: The Romans)
 * The Doctor also accidentally started the Great Fire of London in 1666. (DW: The Visitation)
 * The Doctor saw an alternate Earth consumed by fire. (DW: Inferno) This memory was used against him by the Keller Machine. (DW: The Mind of Evil)
 * Ky used fire to ward of Mutts. (DW: The Mutants)
 * During the Doctor's sacrifice by the Deons, fire was used to burn the ropes holding a rock above him. (DW: Meglos)