Time particle

Time particles were the leftover effects of something being forcibly displaced in time by a time eddy. Anything that travelled through an eddy was coated in time particles and they could be destroyed to reverse the eddies' effects, even retroactively.

The Ninth Doctor detected time particles on a group of Roman Centurions who had been displaced to 1959 London and decided to follow the particles to reverse the events rather than deal with them himself. (AUDIO: Sphere of Freedom) He and Nova later followed a different group of of time particles to Tarlishia where they got the idea to repurpose a fleet of drones to retroactively destroy the time particles on the Sphere of Freedom and fix the time eddies in the past. (AUDIO: Cataclysm) However, doing so inadvertently broke the seal on the Ravagers that were being satiated by the time eddies' effects, leading to the destruction of the universe before the Doctor rewrote the timeline. (AUDIO: Food Fight)