The Start of the Chain of Events

Determinism is a proposition that every event, including human cognition, decision and action are determined by an unbroken chain of prior occurrences. 1) What is the initial event that set out the chain? If it is too simple, then it's no longer qualify a determining event, but eligible to be derived varies of following ups; if it's not simple enough, then it requests another prior occurrence. 2) What are the differences between determinism and fatalism?