The Advent of The Tower

In the early days of existence, the only living, thinking creatures were clumps of sentient mana woven into the natural elements of the primordial material plane. One might argue that not even the gods exist, as there were none who worshipped, although other similar planes cannot be so succinctly dated.
But the mana worked in communes, clumps operating together in simple organizations to make a functional, tactical form. This early basis of life was known as Mortal Forms, the building block of many of the creatures that now inhabit Edda.
Of course, life has gone a long way since then, and most people will find they have organs, blood, and flesh as opposed to clumps of mana and various materials.
There is one reason for this distinct difference, The Tower.
It is unknown exactly when this incident occurred, as there is only a handful of actual records about it, and even those are merely by chance, but on a random day estimated to be roughly 900,000 years before the current era, a strange Tower apparated in midair above the continent of Edda.
This Tower was a strange, smooth stone structure, that was impenetrable from all sides and slowly drove itself down into the land beneath it. Once it successfully landed, a large shockwave of alien energy pulsed throughout Edda.
This shockwave is what is responsible for the change of the Mortal Forms, as once it passed over them, the clumps of mana ceased to be a group of autonomous lifeforms and instead transmogrified into a single, flesh being, with organs and blood, with a singular mentality. 
The only reason we have records of this time is due to the directives the Mortal Forms left behind, forming the instincts to preserve legacies, survive, and discover more. For this reason, this change and the events that came afterward were kept in a sequence of cave murals.
Once The Tower landed, a strange individual calling itself The Navigator made itself known, offering Power, Riches, and 'Notoriety among the Cosmos' to the newly invoked Mortals. However, being a new species, with only minor primal directives on survival, these words meant nothing to them, and within 7 Days Time, The Tower disappeared from the land.
But its effects lasted forevermore and led to the creation, and then evolution, of the races of Edda to the present day.

Summary

When mortal life was still mana and materials, a mysterious alien Tower descended upon the land of Edda, sending a shockwave of magical energy throughout the world, transforming that mana and materials into flesh and blood of mortal species.
The Tower itself promised a treasure trove of rewards, but the newly created mortals had no concept of those things, and it left without further exploration, leaving a plethora of new creations with a drive to preserve, learn, and survive the eons.

Historical Basis

Talented Diviners, Mana-Readers, and Archaeologists have in unison found trace records of chaotic energy, past memory fragments, and cave paintings to prove at the very least the Tower was present at this time, and carbon dating placed it as far back as the tale attests. However, there is little to know about what truly occurred before, during, and in the intervening lost millennia afterward.

Spread

The Advent of The Tower is known to almost all educated folk throughout Edda, serving as the tale of creation for all living people in the modern-day.

Variations & Mutation

There are very few variations in the actual telling of The Advent itself, its few facts are recorded history, but there are a handful of differences in if the Tower was breached at all, or if no one claimed its riches. What comes after The Tower left as well is the spawn for many of the world's religions Origin Myth.

Cultural Reception

Many individuals are entirely neutral about The Tower, viewing it as a vague tale of origins that might not even be true, but many scholars of Avalon and The Cabal of The Night Sky view it as a premonition and are wary about The Towers possible return.

In Art

Towers and other spiraling buildings have long since been a symbol of intelligence and grasping the future, as The Tower offered wealth and prizes to those who conquered them.

Date of First Recording

900,000 BC

Date of Setting

Before 900,000 BC