By the time of Morbius's attempted re-birth, Karn had become a burned-out and exhausted planet, a barren and rocky wasteland with many ruins and abandoned industrial plantations. It was littered with the wreckage of crashed spaceships brought down by the Sisterhood out of fear of theft of the Elixir of Life.
Karn was originally a colony of the old Gallifreyan Empire in the days before Rassilon. The Sisterhood of Karn were a remnant of the Pythias who once ruled Gallifrey before being expelled by the triumvirate of Rassilon, Omega, and the Other.
In the Rassilon Era, the Sisterhood guarded the Sacred Flame, which was used to distill the Elixir of Life, which could aid a Time Lord who experienced difficulty with regeneration. In the far future, Morbius, a renegade Time Lord, in his bid for galactic conquest, came to Karn with a mercenary army promised the Elixir of Life. The Time Lords cornered him there, defeating, trying and executing him.
Before his death, Mehendri Solon, a member of the Cult of Morbius, removed his brain and preserved it, vowing to resurrect him. Solon settled on the planet in a disused hydrogen plant and sought a way to make Morbius live again, using body parts from dead crew members of crashed ships to create a new body for him. Cristophe Zarodnix purchased Karn from the Sisterhood, which was something of a bad deal, as they knew the planet would be ravaged in the Last Great Time War.
Eventually the Sisterhood reclaimed the planet after the Time War, and rehabilitated its ecosystem. While still harsh, it is now verdant and majestic as well.