The Time Portal was unexpectedly discovered by the scientists of the FERMI Particle Accelerator. They found a fracture in time that made it possible to construct a portal into primeval history. Scientists decided to send a probe into the portal, to see the conditions on the other side. They could not locate the probe, so they concluded that it had arrived in a separate timestream, meaning that they could travel through it and not alter the future. With this information, they sent several Pilgrimages through the portal so that they could live in the colony of Terra Nova in a chance to reconstruct humanity.
For most of the first season, it was the common understanding of the people of Terra Nova that communication with the 22nd century was only possible when the portal is open, so that if people in Terra Nova needed to request certain supplies or recommend certain people in the 22nd century for recruitment, they would have to send the request during one Pilgrimage and wait for the one after that for the supplies/people to be sent. However, as shown in "Proof", Mira had a method of communicating with the future that did not require the portal to be open, and as shown in "Vs.", Lucas Taylor was working on a way to make the portal two-way, so that matter and people as well as signals could be sent from Terra Nova back to the 22nd century. Lucas finally succeeded in doing so in "Within", where he returned through the portal back to 2149.
The device used to access the portal in the 22nd century was located at Hope Plaza. Hope Plaza and the device used to access the portal at the 22nd century side were destroyed when Jim Shannon set off a Pyrosonic bomb to prevent the Phoenix Group and its associates from invading Terra Nova and taking its natural resources. ("Occupation-Resistance")
There is a much smaller connecting portal device known as the Portal Terminus on the Terra Nova side that was sent from Hope Plaza in pieces after the Fourth Pilgrimage. Lucas Taylor takes control of it, and during the confrontation with him and his father and Jim Shannon, he uses it to transport himself to 2149. When the Eleventh Pilgrimage comes through, the bomb strapped to a man destroys the Portal Terminus. Lucas and the Phoenix Group bring a new one that can go both ways but is damaged by a Carnotaurus. Malcolm is forced to repair it and the Portal Terminus is then used to ship three cargo containers of meteoric ore and another container with a hidden Jim and a Carnotaurus in it. Malcolm then destroys the disables the new Portal Terminus, and the portal becomes untethered.
- Nathaniel Taylor was the first person to enter the time portal. According to executive producer René Echevarria in this Q&A, the failure to find the probe told them that the portal led to a different time-stream, but "The first people who went through didn’t know where they were going to arrive".
- This tweet from InsideTerraNova (which seems to be a legitimate account of the show's creators, since it is followed by the show's official twitter account TerraNovaonFOX) says "The rift opens at regular intervals that we can't control -- only predict and anticipate."
- In this interview with executive producer Brannon Braga, the interviewer asks "On Terra Nova, are there limits to what supplies they can bring from the future?" and Braga answers, "Yeah. The portal, when they dilate the time fracture, it can only stay open for 18 minutes. So as much as you can get through and that will fit. A lot of the stuff they build they have to build there."
- On the show, the history of the portal is briefly summarized by an announcer on a giant screen in Hope Plaza, who says "Twenty-two years have passed since scientists first realized that subatomic experiments uncovered an unexpected phenomenon. Physicists characterize this anomaly as a fracture in the fabric of time and space." The fact that the experiment was at the FERMI particle accelerator is mentioned in FOX's press release for the show. Particle accelerators are generally giant circles, so the two giant circular structures on either side of the Hope Plaza complex where the time portal is housed presumably represent the FERMI particle accelerator.
- Some dialogue in the control room refers to the portal having an event horizon (as does a display shown in closeup later), and also mentions that the portal is only a few microns in size before being dilated to a size people can travel through: "Event horizon is at 0.6 microns. 0.7, holding at 0.7." "Standing by to initiate portal dilation." "Terminus is steady." "Initiate portal dilation."