Origin of life on Earth is not accident. Its emergence was inevitable as soon as there were favorable conditions for the environment. All this is the investigation of fundamental laws of science.
The first steps of life on Earth
In spite of the fact that Earth during the early period of the existence often was exposed to asteroid bombings, had strong volcanic activity, was hotter and deprived of oxygen, life on it after all arose and evolved.
In general it is possible to tell that in stable conditions and at the correct temperature as a result of chemical reactions there can be molecules which are capable to reproduce themselves, causing further transformations. For our planet the atmosphere saturated with hydrogen, ammonia and methane and also huge oceans of water became such conditions. Molecules could "eat" energy from hydrothermal sources, and subsequently became construction blocks for proteins and nucleinic acids.
As soon as the first molecule was created as a result of these accidental chemical reactions, the subsequent succession of events was not based on accident any more. Instead evolution and natural selection came into force. Molecules which could replicate began to breed quickly. Then all types began to fight for available food. Less effective types died out.
Carbon – a basis of all
Carbon is atom which deserves specific mention as it has the properties allowing it to be grouped in the sequence: "chains" and "branches". It allows other molecules "cling" for these obrazoavaniye that, in turn, creates complex molecular structures. As some molecules constantly increase, after all, reach the determined "critical size". The communications holding atoms together weaken and the molecule breaks up. In certain cases two almost identical molecules turn out. Each of these molecules seeks to attract similar molecules from surrounding space. Some do it successfully. Such molecules grow again and reach "the critical size", and then break up to two parts. It is infinite process. Life could begin thus. The cycle based on natural chemical reactions which repeated again and again. Then there were other elements which helped to support and complicate a cycle. The attempt to define a chain of events which led to emergence of life on Earth is a difficult task. Significant progress was made in theorizing and reconstruction of the process which led to emergence of the simplest life forms. But, at the same time, scientists have no exhaustive data on each stage of development. Gaps in knowledge can be filled only with guesses now.