I think 6000 years mean that the world start to filled in by civilized human (Adam and Eve) and start growing.
That 0 of 6000 years ago means the first civilized human is created/born.
I do not know what happen before more than 6000 years ago. Could be a dinosaur times or bigbang etc you call it.
But that is what I believe about 6000 years of mankind walk on this earth. =)
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