In C.S. Lewis’s fantasy novel The Magician’s Nephew, the world destroyed by Jadis before she reaches Earth is called Charn.
Charn is an ancient, lifeless world visited by Digory Kirke and Polly Plummer through magical travel between worlds. They find it abandoned except for Jadis, its last queen, who has preserved herself in a state of suspended animation.
Jadis explains that she destroyed Charn by using the Deplorable Word after a conflict with her sister. The act ended all life on the world, establishing her as a dangerous and morally destructive figure before the creation of Narnia.
Charn is not Narnia. Narnia is created later by Aslan’s singing, while Earth, called our world in the novel, is the place where Digory and Polly begin their adventure. Jadis eventually becomes the White Witch of Narnia.