Time portal A time portal is a gateway to other times and dimension s . Encounters . In the 31st century , artificial time portals were utilized by temporal agent s in their attempts to protect the time stream from temporal incursion s . When transported Jonathan Archer from the year 2152 to the 31st century to protect him from the Suliban Cabal , he inadvertently affected a change in the timeline through Archer ' s removal , altering history in such a way as to destroy his own civilization . This left him with no way to correct the damage , as all of the time portals had also been destroyed . The timeline was eventually restored when Daniels used a device to turn the Humanoid Figure ' s temporal chamber into a temporary time portal that allowed Archer to return to his own time period . ( ) In 2267 , the crew of the first encountered the Guardian of Forever , a sentient time portal capable of communication . With help from the Guardian , Captain Kirk and Spock were able to correct a change to history inadvertently affected by Doctor McCoy . ( ) In 2269 , Kirk , Spock , and McCoy discovered a time portal in use on the planet Sarpeidon , which was being used by the planet ' s inhabitants to travel to various points in their planet ' s past to escape the impending supernova of their sun . Utilizing this method of time travel required processing through the atavachron , a device which altered one ' s cellular structure and brain patterns for survival in one ' s selected time period , but also prevented one ' s return through the portal . If not processed through the atavachron , one could only survive in their time period for a matter of hours . Kirk , Spock , and McCoy accidentally traveled through the portal , Spock and McCoy arriving 5 , 000 years in Sarpeidon ' s past . While there , Spock began to regress to the behavior of Vulcan s of that time period , displaying increased emotionalism and an inability to control his aggressive tendencies . Eventually , all three of them were able to return through the portal , as they had not been processed through the atavachron . ( ) Later that year , they observed the dawn of the Orion civilization by going back in time via the Guardian , only to find that Spock had died as a young boy and an Andorian , Thelin , held his position of the " Enterprise " ' s first officer . Spock subsequently traveled back through the portal and successfully altered history to ensure his survival . ( ) In 2374 , an ancient time portal constructed by a race which disappeared two thousand years previously was discovered on the Bajoran colony world of Golana . While vacationing on the planet with her family , eight year - old Molly O ' Brien fell into this portal and was transported three hundred years into the past . Modulating the portal ' s temporal field generator s and reactivating the portal , her father , Chief Miles O ' Brien , used a transporter beam to retrieve Molly , but did so from a point in time after Molly had already spent ten years living by herself . The O ' Briens initially attempted to help Molly reassimilate into society , but when it became clear that she would not be able to , they sent her back through the portal , recalibrating the temporal field generators to send her back to the same point in time from which they had originally retrieved her . Unknown to the O ' Briens , though , the recalibration didn ' t hold , and the portal actually sent Molly back in time to a point shortly after she first arrived . Encountering her eight year - old counterpart , Molly sent her back through the portal to be reunited with her parents . This had the effect of changing history , and erasing the eighteen year - old Molly from existence . ( )