All elemental planes are places of continuous destruction and rebirth; their element is continually being destroyed in sinks and spat out again in other forms by sources all across the plane, although the forms these sinks and sources take are always different from plane to plane. Likewise, a sink or source seldom stays in the same place, and often disappears entirely or opens out of nowhere. Sources act to counteract sinks, removal of material from the plane, and destruction through effects like Disintegrate, and so every plane actually has more sources than sinks at any given time, at least if you consider amount of material produced or consumed. These Planes also all have traits to enhance appropriate magic and impede opposite magic, and are all quite sparesely populated.