Originally Posted by
Aucald
According to "Chronicle Vol. 1", prior to the Ordering (when the Pantheon came to Azeroth) the surface of Azeroth was essentially barren and had little to no organic life - the Elementals, enslaved by the Old Gods, just warred across its surface to entertain their Old God masters while the Old Gods themselves went about the business of corrupting Azeroth's World-Soul while also fighting amongst themselves to see which one of them would be dominant in the end. The presence of the Old Gods did give rise to some forms of organic life themselves: the K'thir, the N'ragi, the Aqir, and the C'Thraxxi - all of them abominations made of the Old Gods' flesh and ichor. Whatever original life Azeroth might've had at this point, such as life arising from the shards of Light in the primeval ages of its creation, were likely destroyed or corrupted by the Old Gods to give rise to their own creations above.
When the Titans came, they killed Y'Shaarj first (the greatest of the Old Gods at the time) from high orbit, an act that wounded Azeroth severely and created the Well of Eternity as pool of the World-Soul's own essences (Spirit and Arcane energies). As killing the Old Gods directly proved too costly to the nascent World-Soul, they opted instead to create armies of Titanforged to destroy the Old God's servants, contain the mass of their corrupted forms, and then imprisoned them in Titan installations across Azeroth - sealing their corruptions away within the planet itself, safeguarded from further spread by the prisons themselves.
Once the Old Gods were dispatched and the raging Elementals that couldn't be pacified imprisoned in the Elemental Planes, the Pantheon set about the work of Ordering Azeroth and seeding it with uncorrupted life. Eonar and Freya were responsible for the bulk of this, and Freya herself is credited as the creator of the Wild Gods. Using the energies of the Well of Eternity directly, Freya created vast enclaves and reserves of uncorrupted nature, which gave rise to animal life on Azeroth. The Wild Gods were the largest and most powerful of these beings, infused by the energies of the Well and gifted with sentience and power. So the phrase "emerged from the Well" isn't meant to be literal here - the Well helped give rise to them, but they were created by Freya and first appeared form the wilds that she and Eonar seeded across the world.
As life proliferates from these enclaves, the ambient energies of the Well change it further, giving rise to beings like Trolls, Yaungol, Furbolgs, Murlocs, and some of the other older races of Azeroth. In addition it seems the Wild Gods themselves had some influence on life, either creating or finding beings to serve them (which is where many of the Greater Loa arise from). Later on Yogg-Saron's Curse of Flesh causes the creation of organic life through converting the Titanforged - creating Vrykul, Dwarves, Troggs, Gnomes, and eventually Humans. Organic life once more proliferates across Azeroth, evolving and changing forms due to a variety of causes.