"At the beginning of our universe, the Big Bang, matter started as fundamental particles, very simple. As time went forward, more complex atoms formed, hydrogen, one proton being circled by one electron. Eventually the force of gravity caused hydrogen to form stars and these stars became giant fusion reactors. The hydrogen fused into helium. Helium into lithium. Eventually these stars formed more complex elements and formed iron. The iron caused the stars to condense into such a tight ball that energy pushing out caused the star to explode, and during this explosion all the heavy elements were formed and were spread throughout space. More stars formed using this materials and planets began to form too. On one of these planets, carbon began forming complex molecules and life started. Life started simple and got more complex starting from bacteria, to worm, to fish, to reptile, to mammal to human."
This is true, but there's something you haven't thought of yet. The very same reasoning which leads you to atheism (and myself as well until a few years ago) leads to a very different, surprising conclusion if thought through a little bit further.