Gaia IV

Gaia IV is a Class M planet and the fourth in the Gamma Quadrant's Gaia system. The planet is surrounded by an unusual energy barrier which includes a temporal anomaly.

In 2373, the crew of the USS Defiant (NX-74205) (I) visited the planet and discovered that it was home to eight thousand inhabitants. The inhabitants were in actuality the descendants of the Defiant crew, in a timeline in which the starship was sent back in time to the 22nd century when it encountered the temporal anomaly upon attempting to leave the energy barrier. The inhabitants were erased from existence when the Odo who lived on the planet changed the course of the Defiant to avoid the temporal anomaly. The crew of the Defiant retained their memory of the inhabitants of Gaia IV. 

Starfleet later ordered a quarantine of the planet due to the energy barrier and the temporal anomaly. 

Gariff Lucsly of the Federation Department of Temporal Investigations thought the causal loop experience by the crew of the Defiant at Gaia IV was one example of how conscientious the Deep Space 9 crew were towards the timestream.