Time Portal

The Time Portal is a bubble-like doorway through time and space that Nigel Marven uses to save prehistoric creatures from extinction.

Properties
The Time Portal is transparent and expelled a bright light when open. It is concave-circular in shape and the core of the Portal ripples like water whenever anything passed through it. Occasionally, a blurry image of the other side was also visible. Humans, animals and objects could travel through the time portal simply by passing through one side to the other; however, gases and debris could not enter (PP: T-Rex Returns, PP: Dinobirds). While the 'home' side of the Time Portal was fixed to the observation pen complex in Prehistoric Park in the 21st Century, the exact location in time and space that the Portal leads to can be changed, with the least known amount of time being 10,000 years ago and the greatest amount of time being 300 million years (PP: A Mammoth Undertaking, PP: The Bug House). It was unknown if the Time Portal could be calibrated to open to the future.

Time Portal sticks
The Time Portal itself was activated by placing two silver sticks in the ground, approximately 4 metres apart, and priming both of them by twisting the shaft upwards and counter-clockwise. Once the sticks were primed, several blue lights at the tip of the stick would turn on and the Portal can then be opened by using a remote control (which presumably could change the destination time and location).

Altering history
Any adventure Nigel had into the past, and any creatures he removed from their time periods, did not have any apparent alterations/ramifications on the present. This would indicate that the Time Portal did not have any paradoxical effects on the timeline, meaning anything Nigel did or took from the past, had already happened. This form of time travel is referred to as a "causal loop."

Critical Response
As arguably the most important plot device in the series, the Time Portal has been scrutinized by critics and viewers. Common Sense Media stated that "the time-travel angle results in a slew of unanswered questions for those with a logical bent." The YouTuber HoopsAndDinoMan offered a dissenting view, stating that "the makers of the show know that time traveling is just a plot device and not the focus of the series, which I thought was a smart move."

Trivia

 * The time-travelling Anomalies in the si-fi drama TV show, Primeval, were similar in appearance and sound to the Time Portal.
 * Ironically, both Prehistoric Park and Primeval were produced by Framestore and Impossible Pictures.
 * The Time Portal was originally supposed to be hooked up to a large machine, but the idea was scrapped before production.