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Answer:
Last episode name of tenth season was 10x20 Unending.



Story plot: Asgard decide to share knowledge with humans because they are about to make a mass-suicide. A ori ship started to hunt the "Oddyssey". Samantha Carter used the Asgard time dilation technology to slow down time to plan an escape from their certain destruction. Sam found the solution but it was too late and they were in the ship until they became old. Daniel fell in love with Vala. Sam learned to play the violin. Mitchell had the first signs of Alzheimer. In the end Sam found a solution to go back in time. But someone had to stay old to tell the solution to other SG-1 members (That will forget everything). Teal'c accepted. He stepped in a force field that isolated him from the time dilatation. When he got back in time, Teal'c immediately told the solution to Carter and the team was saved.

First answer by Jardax. Last edit by Tracertong. Contributor trust: 10 [recommend contributor recommended]. Question popularity: 7 [recommend question].