The origin of life is the biggest unanswered question in biology. Evolution explains the origin of all species once life has started, but there really is no good theory that explains exactly the steps that created life on earth. There is the RNA world hypothesis which supposes that before life was based on DNA and proteins, the world only had RNA which acted as both a replicator and an enzyme. But there really is not good theory that explains how you go from a soup of amino acids and nucleotides to a cell wall enclosed RNA world living organism. The transition from RNA to DNA is also not clear.
PS: I am NOT claiming that we need a "creator" or god to explain the origin of life. I am sure there is a natural non-theistic solution to the problem but we just don't really understand the mechanism behind the origin of life at this point in time.