There is a set of scientific theories about origin of life on Earth. However most of modern scientists consider that life arose in warm water as it is the most favorable environment for development of the simplest unicells.
Theory of "primary broth"
The Soviet biologist Alexander Ivanovich Oparin in 1924 created the theory about emergence of life on our planet by means of chemical evolution of carbon-bearing molecules. He entered the term "primary broth" for designation of water with high concentration of similar molecules.
Presumably "primary broth" existed in small reservoirs of Earth 4 billion years ago. It consisted of water, molecules of the nitrogenous bases, polypeptides, amino acids and nucleotides. "Primary broth" was formed under the influence of the space radiation, high temperature and electric discharges.
Organic matter arose from ammonia, hydrogen, methane and water. Energy for their education could be received from lightning electric discharges (lightnings) or from ultra-violet radiation. A.I. Oparin assumed that filamentary molecules of the received proteins could be turned and "stick together" with each other.
In vitro scientists managed to create similarity of "primary broth" in which congestions of proteins were successfully formed. However the issue of reproduction and further development of koatservatny drops was not resolved.
Proteinaceous "balls" attracted to themselves molecules of fats and water. Fats were located on the surface of proteinaceous formations, covering them with a layer which on structure bore a faint resemblance to a cellular membrane. Oparin called this process coacervation, and the formed congestions of proteins – koatservatny drops. Over time koatservatny drops absorbed all new portions of substance from the environment, gradually complicating the structure, did not turn into primitive living cells yet.
Origin of life in hot springs
Mineral water and hot geysers which are especially saturated with salts can successfully keep primitive life forms. The academician Yu.V. Natochin in 2005 assumed that not the Ancient ocean, but a warm reservoir with prevalence of ions of K+ was the environment of formation of live protocages. In sea water Na+ ions dominate.
The theory of the academician Natochin is confirmed by the analysis of maintenance of elements in modern living cells. In them as well as in geysers, K+ ions prevail.
In 2011 the Japanese scientist Tadashi Sugavara managed to create living cell in the hot mineralized water. Primitive bacteriological formations are stromatolita and are now formed under natural conditions in geysers of Greenland and Iceland.