What if we adopted a dating method around the accepted innovation of writing?

What comes before the advent of the written word is generally considered as 'prehistory', and what comes after is 'history'.

So, if you can find an accepted time frame for when that occurs, you can then build a basic dating stem around it.

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Angel of the Abyss
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"I am Ripper...Tearer...Slasher...Gouger. I am the Teeth in the Darkness, the Talons in the Night. Mine is Strength...and Lust...and Power! I AM BEOWULF!"