What is the scientific theory on the origin of life?

It is debatable how and where a biogenesis occurred, but most scientists agree that one happened because it is required for the naturalistic worldview.

In the Miller-Urey experiment, which tested the theory that life originated accidentally in a warm primordial pond, Miller and Urey synthesized organic molecules required for life, based on the theory that the composition of the early earth's atmosphere was highly reducing, similar to that of the universe.

The Miller Urey experiments, though commonly used in textbooks, have been rejected as a legitimate means of explaining the origin of life by the majority of scientists; nonetheless, the assumptions of a reducing atmosphere have been proven incorrect.

The warm pond theory was essentially a protein first theory. It postulated that proteins formed in solution spontaneously and formed proto cells, which then used the energy of the organic molecules in the solution to sustain themselves. The problem with this theory is that proteins would not be able to replicate themselves, nor would they contain the information required for life's replication and maintenance.

The DNA first theories have even more flaws: proteins are needed by DNA to replicate the information in the DNA; without these specialized proteins, DNA would not have the protection from the environment required for life to continue, even though it contains all the information needed for life.

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 a non-oxidizing environment, is an unanswered problem. RNA is the most likely candidate for the origin of life because it is an informational code that some viruses use for reproduction. RNA also has limited enzyme like activity.

In summary, the theories of a biogenesis were severely damaged by the evidence that the highly reducing atmosphere required by the Miller Urey experiments never existed. There is no conceivable explanation for how life could arise from nonlife by completely naturalistic random events.

The scientific theory on the origin of life is called abiogenesis, which proposes that life arose naturally from non-living matter under the right conditions on early Earth.