The world that was and death before sin

Hi fellows,
I’m searching and they tell, that the world that was (2 peter 3:5-7) is not biblical because it crashes against That due to sin death is generated. I’ve read the studies of Bran.
I’m reading Genesis 3 and I don’t find where it says that death is because of sin.
I firmly believe in the world that was.
Due to the fall of satan we’re here. Ok. Then God flooded the world that was and everything perished. Here we have it. But first was the sin of satan and his rebellion.
Other thing were the dinosaurs, they were living and the meat eaters were killing the others. The flood (of 2 Peter 3) came and all dead.
On the other hand, Job 38 what does it mean? When were they in that moment? It must have been in the world that was and the first earth age.
Excuse me I’m a bit lost