The Mana stream

The flow of Mana.

The mana stream is a large never ending flow of Raw Mana. The stream flows throughout the universe and spreads its mana into as many planets as it can. Once the stream passes through a planet, it will form a circular flow around, and into the planet.

Planet Connection and reliance

Once the stream forms a connection to the planet, it will start to feed mana into the air of the planet, for it to be used by plants, animals, or people. Depending on what the mana is absorbed by depends on how its used, plants or animals can use it to sustain themselves even in harsh environments, while people can use it to preform magic.
However, once the mana is absorbed, a genetic reliance on mana develops. If they lack a soul, or Pure Mana, they will degrade into something lesser, or die completely.

Source of the Mana Stream

Every branch of the mana stream could be led back to The Grand Arcane. The Grand Arcane is responsible for pumping the mana into the stream, constantly cycling more.

Souls

Souls are the direct source of Pure Mana, when a person dies, their soul is released into the air, to be absorbed into the Mana Stream, where it's excess Pure Mana is filtered into the Mana Stream itself, and the soul passes on into the Astral Realm.
Dark Souls cannot be put into the Mana Stream, or else their corrupted mana would tarnish the Pure Mana in the stream, and spread the darkness, so instead, the Mana Stream naturally rejects Dark Souls and sends them to the Void, to become Corruptives.