To be technical I'm an agnostic atheist; which just means I don't believe there is a God, but I don't discount the idea that there could be.
I haven't always been agnostic, I was raised as a casual Christian (basic christian beliefs but without the exposure to church) A have a few great uncles who were pastors and one who was actually a Dean at a theological college.
When I was young the bible made perfect sense, then as I got older and I began questioning things, I noticed a lot of hypocrasy and error in the teachings.
One example is Noah's ark, which from a Fundamentalist standpoint could never fit ALL species and variations of species on a boat of it's given dimensions. Not to mention the food needed to sustain them for over a year. Along with many oversights that would have been permissable to an ancient culture but is now known to be false.
If taken from a more flexible standpoint that they are stories to be interpreted; than that obviously shows the books are not the word of God, just man-made stories. In which case, why believe any of it?
Then there is also the matter of scientific discovery 'debunking' biblical ideas. Unlike 2000 years ago, we know where lightning comes from, rain, how to cross breed animals and plants, the rotation of the planets, the chemical make-up of our atmosphere. Even the stages of pregnancy and conception.
Whereas nothing has ever been re-attributed to God.
Scientific Hypotheses (assumptions) and Theories (Proven assumptions) are under -constant- testing and re-evaluation to come to the most right answer we can discover. While a religion can only thrive with a lack of honest testing and skepticism.
When it comes right down to it I would rather live a life experiencing the world and trying my best to better it than to cling to a set of pre-medieval rituals and beliefs designed to keep oneself subserviant.
Just to make it clear. I would prefer if there was a God who was personally interested in my welfare and could offer me an afterlife instead of blank oblivion. I just don't see the evidence to support such a deity.
1) Where the Big Bang came from and what caused it, there are a few hypotheses... no one knows for a certainty. We might find out eventually, we might not. In my personal life if has no bearing lol. The fact that it's impossible to know right now is the only reason I continue to classify myself as an Agnostic
2) As for RNA 'poofing' into existence. It's believed that the combination of electrical storms, volcanic activity and abundance of water created Amino acids and other products of very basic life.
That hypothesis is supported by the 'Miller-Urey' experiment conducted in the 1950's
It has since been re-tested over the years and the conclusions have been the same.
Source:
http://en.wikipedia.org/wiki/Miller%E2%80%93Urey_experiment