Revealing mistake: When Benton jumps over the maggots to get into the cave the Professor and Jo are hiding in, the jump causes the floor to move, giving away the fact that the floor is wood covered by a small amount of gravel.
Revealing mistake: In the finale, when Stevens is beating on the computer console, it moves around quite a bit, even thought it is supposed to be a strong and stationary object.
Revealing mistake: At the end of episode five, when James collapses against the wall, it wobbles under his weight.
Revealing mistake: Matte halos appear very frequently in this episode, particularly when descending into the mine shaft.
Revealing mistake: When Jo and the Doctor are rowing through the maggot lake, several times parts of the actor's arms disappear.
Answer: It was never destroyed on-screen; it was intact at the end of the TV movie, and destroyed by the start of the 2005 series. It was destroyed in the novel "The Ancestor Cell," but in a completely different manner to what happened in the series.
DaveJB