The Impact Crater, later known as Tallon IV's Scar, is the final location visited by Samus during the events of Metroid Prime. It was created when a Leviathan from Phaaze impacted Tallon IV. It is the only known location of Orange Phazon. This is where Samus faces the Metroid Prime in a final confrontation.
Because of the elevated concentrations of Phazon, the Impact Crater is inhospitable to nearly all life. However, Lumigeks and Fission Metroids, which cannot be found anywhere else on the planet, live here.
The Impact Crater was sealed by the Chozo, using the twelve Chozo Artifacts and the Artifact Temple. This served to slow the spread of Phazon over Tallon IV. This may be why the inside of this crater is so different from the ones in Metroid Prime 3: Corruption. The Phazon produced by the Metroid Prime had nowhere to go, causing extreme concentration.