Temporal contamination occurred on January 9th, 1961 when a field agent, Commander Alex Tomlinson, was participating in a long term investigation of anomalies in the mid 20th century (1957-1963). Sensor sweeps detected a number of markers indicating temporal activity in that time period, specifically in the United States on Earth but were unable to pinpoint a source. That period of time has a good number of high level inflection points which made temporal calculations difficult.
Cause
Alex Tomlinson was assigned to investigate the potential for temporal activity in and around the movie industry at the time. The investigation was going well but eventually the cover became quite stressful for Commander Tomlinson. His cover identity of Gene Roddenberry was involved with 2 different women with orders from the operations commander to get closer to both. Tomlinson began to show signs of stress related psychological issues and revealed to his commanding officer that he should be pulled out as soon as possible, saying that he was loosing touch with what side he was one. His commanding officer chose to schedule him for extraction but the extraction point was pushed back several times.
Asset Goes Missing
Commander Tomlinson began to have only erratic contact with his superiors in early 1964. His commanding officer still declined to remove him, against the recommendations of the executive officer of the operation. Tomlinson severed contact late in 1964 forcing the command crew to locate him using the emergency transponder. Upon finding the transponder they found that Tomlinson was starting to go native and had already begun to think of his real background and real life as a fantasy translating those memories into the basis for a fantasy world to write about.
Result
The result of the incident is that Tomlinson, then fully believing himself to be Gene Roddenberry, had completely pushed away his real self and adopted the carefully crafted identify provided for him by Solas Tempus. Since the identity had a full suite recursive background provided to him including military service records, photos, and even people who could personally vouch for his background created for him the identity was a believable one. By the time Solas Tempus had a handle on the contamination done, the information was becoming integrated into the timeline and pulling Tomlinson out could have proven more dangerous than leaving him in.
Historical Changes
Originally TV shows of the time period showed a leaning toward the kind of idealized environment that Tomlinson's alter ego, Roddenberry, created. While the show Star Trek and associated material is not in the historical account there was a need in society for something in media portraying what the world could look like and a desire for entertainment to begin to tackle challenges of the day in a new way.
The entertainment programs created by Tomlinson's alter ego followed extremely closely to those of the history of Starfleet Command and the United Federation of Planets closely but were determined to have little impact on the timeline. It is theorized that this could be an example of a Predestination Paradox causal loop as the impact to the timeline should have been disastrous.