What is the scientific theory on the origin of life?
First scientific theory on origin of life came from Russian biochemist Alexander Oparin which stated that first life on earth appeared through chemical evolution .
Chemical evolution theory supports evolution of life through abiogenesis. Oparin's idea received immediate support from Haldane who also thought that life evolved through abiogenesis in primitive ocean which was described as hot prinordial soup by Haldane himself.
Scientific proof in favour of chemical evolution theory came much later through innovative simulation experiments , conceptualised and pioneered by Harold Urey and Stanley Miller in 1950s. Such experiments were conducted in flasks containing gaseous mixtures, closely mimicking primitive atmosphere of earth.
Such simulation experiments showed that biologically important organic molecules like amino acids could have been generated in a reducing primitive atmosphere. Those molecules also generated polymers like proteins. Aggregated protein molecules formed coacervates in the primitive sea; eventually lipid bilayer appeared around coacervates.
Chemical evolution gave rise to nucleotides and first nucleic acid was definitely RNA , which in the beginning of life on earth acted both as a genetic material and as an enzyme inside the first generation of cells.
There is no generally accepted theory of the origin of life.
Most scientists accept that a biogenesis occurred because a biogenesis is necessary for the naturalistic worldview. How and where a biogenesis occurred is under debate.
Darwin first proposed that life occurred that life happened by accident in a warm primortal pond. This idea was tested by the Miller Urey experiment. Using the theory that the early earth's atmosphere was highly reducing similar to the composition of the universe Miller and Urey were able to synthesis organic molecules that would be necessary for life.
However the assumptions of a reducing atmosphere have been proven wrong. The Miller Urey experiments though widely used in textbooks have been rejected as a valid means of explaining the origin of life by most scientists.
The warm pond theory was basically a protein first concept. The idea was that proteins were spontaneously formed in the solution and formed proto cells. These cells used the energy of the organic molecules in the solution to maintain themselves. the problems is that the proteins would have no means of replicating themselves.
The information necessary for the replication and maintenance of life would not be formed in proteins.
The DNA first theories have even more problems. DNA while having the information need for life would not have the protection from the environment needed for life to continue. Also DNA must use proteins to replicate the information in the DNA. the specialized proteins would not exist. y
The RNA first is the most likely candidate for the origin of life. RNA is an informational code that some virus use for reproduction. RNA also has limited enzyme like activity, That RNA can function like a protein and like DNA makes it the most likely candidate. However the proteins like enzymic activity of RNA is very limited, and insufficient to function in replicating the RNA. The transfer of RNA which can exist briefly in an oxidizing environment to DNA which can only exist in an non oxidizing environment is an unanswered problem.
In short there is no plausible explanation of how life could come from non life by totally naturalistic random events. The evidence that the highly reducing atmosphere required by the Miller Urey experiments never existed was a blow to the theories of a biogenesis.