Primordial Soup Provided the Compounds From Which Life Arose
During the period after earth had cooled there were many new molecules forming (both organic and inorganic), which later provided the building blocks from which the life originated. Reactions of the gases in the earth's atmosphere, which included carbon dioxide, methane, ammonia, water and nitrogen, resulted on the formation of the molecules. The process of these reactions have been modeled many times in laboratories, as first shown in the Stanley Miller and Harold Urey. In the Miller-Urey experiments, the gases (carbon dioxide, methane, etc.) were combined with steam and then zapped by electricity, and this formed amino acids and other organic molecules. Based off these experiments, scientists believe proteins and other organic polymers were formed similarly with the energy from UV radiation, lightning, or heat from deep sea hydrothermal vents. This sea (or "soup") of organic molecules is often referred to as "primordial soup". By chance, molecules would have eventually been formed that would be able to self-replicate; the key element to the initiation of what we consider to be life. Replicators would first be able to replicate unstoppably, but eventually, as resources became scarce “natural selection” would promote those that were randomly the most efficient and well-suited (THINKQUEST).