What exactly was here before the beginning of the universe

Well by definition the word God means something that has always been there. And your assuming that the entity that has always been there was not there at some point. So your question does not hold much wait.

The only viable answer is the same for both sides.

"We don't know."

I believe it's a mix of both God and science. God might have made it seem "natural" the way the universe was created for many reasons like testing people's faith in him. I've also had the same questions too something can't just come out of no where, it's impossible. Even if you find out what created the primeval atom or God, what created the thing that created God or the primeval atom. It ends up being an endless cycle. The only way to find out is if we die and God does exist he can give us answers.

I believe in Science and God; I believe in the Big Bang Theory and (parts of) the Bible. The original translation of the bible said God "set the world into motion." So, I believe God created the universe. I have no idea what created God; maybe another god who was created by another God and it goes on and on. But really, we have better things to do with our time then wonder how we got here; for example, I like shoe shopping and RHPS and lazer tag.

According to the Big Bang model, the universe was originally in an extremely hot and dense state that expanded rapidly.
So technically before it expanded, the only thing that was around is dense hot substance (material).
A little hard to imagine, isn't it?

Particles did not appear until after the start of the big bang, and when they did appear they didn't have infinite mass. There was no chain reaction, and there was no explosion because initially there was no space for anything to explode into. The big bang created space. So you're starting off with misconceptions about big bang theory.