Currently, there are many theories of the origin of life, but none of them is convincing.
The monkey argument
There is a "murderous" objection to the atheistic theory of the origin of life without the participation of the Demiurge (Creator): the spontaneous formation of a hereditary DNA molecule from carbon, nitrogen, hydrogen and oxygen atoms has a probability of 10 to minus 100 (or 1000, it does not matter) degree … In terms of time, such self-assembly took much longer than the lifetime of the universe.
A close probability, by the way, is the act of creating the text "War and Peace" by a blind monkey, randomly biting on the keyboard. This argument can be called the statistical impossibility of spontaneous generation of life.
However, the probabilistic approach to the mystery of the origin of life is not very reliable. For example, an old book by Perelman describes a dispute between a young proselyte from statistics and a professor of mathematics. The first, with glowing eyes, assured the second that the probability of seeing 50 randomly walking after each other without women or children appearing (both were looking out the window at the street) was an insignificant, vanishingly small value. The professor only smiled - and soon a regiment of soldiers marched down the street.
Self-assembly theory
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We do not yet know the mechanism of DNA self-assembly, but it may very well be that the likelihood of this process is increased by some unclear factors - for example, according to Academician Yushkin, the joint adsorption of necessary atoms on pieces of minerals, simplifying the compound reaction billions of times.
In addition, the experience of Stanley Miller, a graduate student at the University of Chicago, is known, who in 1953 filled a flask with vapors of ammonia, water, methane and hydrogen and passed electric discharges through this mixture, similar in composition to the atmosphere of the ancient Earth. Miller got a set of amino acids - the building blocks of proteins. But it is precisely the "way of existence of protein bodies" that the well-known Friedrich Engels called life. And there is no need for dissident irony - squirrels are really one of the foundations of life.
More recently, this experience was repeated by Nature itself in the Chita region: lightning struck a haystack and “produced” a resinous substance, including amino acids. In principle, they could combine into proteins and become the basis of life.
But there are other theories as well.
Creationism
"And he saw that it was good." Life was created by God, who is called differently in different religions. The weakness of this theory is in the absence of evidence and an answer to the question: who (what) created God?
References to the fundamental unknowability of the Supreme Being are somehow not satisfying.
The “intellectual” version of creationism is the statement that the Big Bang, which led to the creation of the Universe, is the act of creation - by the same God. However, this theory does not give an answer to the above question either.
By the way, the luxurious style - "and he saw", "and he said" - is only a mistake of translators from Hebrew. What was mistaken for "i" is just a gap between sentences. Although, you must agree, the more correct “he saw - it's good” sounds somehow not very divine.
An ingenious parody of creationism is Stanislav Lem's story of Professor Dond's meeting with Demiurge. It turns out that life on Earth arose from the fact that Demiurge's eggs were burnt.
Panspermia
A very strange theory that claims that life was brought to Earth from other planets from space. Surprisingly, the natural question is "where did it come from?" the authors of the theory are not at all confused and, it seems, are not even very interested. Although it is clear that there can be two answers to this question: one is creationist (God created), and the other is “atheistic” (appeared by itself).
The theory appeared at the end of the 19th century, and a hundred years later it was developed and actively promoted by the American physicist Carl Sagan, who even came up with a project to search for extraterrestrial civilizations. Sagan believed that life not only originated outside the Earth, but also reached the stage of a technogenic civilization there, which means that the "green men" should be able to receive and send radio signals. However, the little men did not respond, which confirmed the "Fermi paradox" - if there is an infinite number of inhabited worlds in the Universe, then why do we not see them?
However, confirmation of the existence of extraterrestrial intelligent beings can be considered just the fact that they stubbornly do not want to contact us.
Oparin's coacervates
Academician Oparin tried to overcome the “statistical” impossibility of spontaneous generation of life in his theory of coacervates. He suggested that initially proteins and other complex organic molecules could have arisen in the aquatic environment, in the primary ocean of the planet.
This is really possible at least under the influence of all the same lightning. Further, these complex molecules could combine into "coacervates", such large organic formations as dumplings, floating in the primordial broth-ocean. According to this theory, reactions could begin inside the coacervate drops, leading to the formation of even more complex substances, and some of them could leave the coacervate. That is, there are the main signs of life - growth, development, reproduction, metabolism. And since everything happens in a limited volume, the probabilities of reactions increase sharply, and the statistical impossibility is overcome.
The weakness of the theory is its complete speculation and the absence of at least any evidence. Although the main statement - we all came out of the water - most unbelieving scientists accept.
Spontaneous generation of rodents
At the beginning of the 17th century, Van Helmot came up with a funny theory. Moreover, he confirmed it experimentally! The scientist believed that life is formed by itself under suitable conditions. For example, mice appear in a laundry basket with a little millet added and placed in a dark place. The experiment was successful, Van Helmot's cat had a great dinner.
The funny thing is that the theory lasted until the end of the 19th century, until the great Pasteur proved that it does not work even at the level of microorganisms - no microbes appear by themselves in pasteurized (boiled) water.
What is life?
The question of the origin of life is so interesting that a much more important problem lurked in its shadow - what is life? Intuitively, we all somehow know the answer, but we cannot formulate it. At the moment, only a set of properties that a living thing should have has been invented - these are all the same development, metabolism, reproduction. But if we restrict ourselves to these properties, then it turns out that we ourselves have already “like gods” and created artificial life - the same computer viruses that develop and multiply, and generally live their own lives.
By the way, about viruses. These mysterious creatures-substances are both living and inanimate matter. Viruses are DNA molecules in a "bag" of protein - normal, ordinary "dead" molecules. The virus can be isolated from the nutrient broth, dried, rinsed, poured into a dark glass jar and placed on a shelf. And after a couple of years, when needed, mix half a spoonful of this powder with broth again and observe the violent growth of this perfectly living mixture of DNA and protein. The very existence of viruses is a strong argument against the statistical impossibility of spontaneous generation of life.
Terminator model
Soon, very soon biochemists and molecular geneticists will create artificial life. They learned how to make proteins (insulin was synthesized long ago), the DNA molecule was decoded and, therefore, they can reproduce. Then they will somehow stick together and get an artificial virus, then - an artificial cell, and there - artificial hippos, and scolopendra, and Adam and Eve. If by that time physicists learn to move in time, then this couple can be taken (as in the films about the "Terminator") in some XXI century BC. Then life will arise on planet Earth. Finally, the problem of its origin will be solved.