The Icosahedronic Expanse

In the beginning of all, a single die was cast. It had 20 sides, 20 facets that comprise everything in the universe. As the die rolled across the endless expanse of void, it began constructing the multiverses, each roll an entirely separate universal entity. It is unknown how many times the die rolled before shattering into countless pieces...but from the shards came the Five Primal Facets...the original divine representations of everything we know. 
The Expanse
After the shattering of the die, the pieces expanded across the entirety of the multiverses, forming matter, planets, geography, moons, stars, and life. Everything in existence is made up of particles and elements from this original 20-sided dice. Where concentrated bits of this eldtrich matter coalesced, Ferrium was formed. In concentrated locations of void, conversely, Hell Iron was formed. This somewhat explains their inherent magical properties. Many scholars claim this expansion is still occurring, and more and more universes are being formed from that initial shattering. Others, however, claim the opposite, that the universe is contracting, and that we will all one day be reformed in the icosahedron primeval.

Historical Basis

Many scholars who have sought to prove this event actually occurred have hit many confusing and baffling pitfalls. Mathematical and arcane simulations always fall short, potentially because the event occurred in a space and time when the current rules of the universe did not apply. Nevertheless, this is widely the most accepted explanation of the birth of all things.

Spread

Only the most isolated communities have not heard of this explanation of the universe. Adventurer's who return from contact with these isolated communities relay tales that are much more simplistic.

Variations & Mutation

Some have argued that it was a six sided die that was rolled instead of a 20 sided die. Those who follow the 6-Side Apocrypha are called "old-school" and have formed very insular academic communities.

Date of First Recording

The Beginning of Time