The first life on Earth was prokaryotic. There're different theories about the origin of these kinds of cells, among them we can find how it's hypothesized that these basic forms of life came up from other planets in meteorites, what it's known as the panspermia theory of life. On the other, there's said that the primitive conditions after the formation of our planet gave place to cyclic inorganic molecules that replicate themselves in a physicochemical equilibrium, as happens today with the nutrients cycle, for example, and in a primordial soup, these replicated molecules began to conform more complex structures like nucleic acids that lead to the formation of live organisms. Maybe they resulted after those basic molecules were progressively being part of other molecules, and involved other molecules in their basal structures, such as states the endosymbiotic theory. Or maybe the origin of those basic forms of life is the result of these and other theories in conjunction .