DNA, first isolated (though not yet named and described) in 1869, is the complex, self-replicating, double helix, chemical compound which carries the coded instructions for the development, functioning, growth and reproduction of all known organisms (and many viruses).

In discussions about the origins of lifeplugin-autotooltip__plain plugin-autotooltip_bigPrimordial Soup

"In 1953 an iconic set of experiments showed that some of the chemical building blocks of life, such as amino acids, could form spontaneously in the atmospheric conditions thought to prevail on the primordial Earth. This gave rise to the idea that the early oceans were a "primordial soup" from which life somehow emerged. the question arises as to when (and how) it first appeared in the (estimated) 4 billion year history of life on Earth.

The RNA World Hypothesis suggests that DNA evolved from RNA (a single stranded coded compound that can also self-replicate) but the details of exactly how this could happen are currently unclear.

The properties of RNA make the idea of the RNA world hypothesis conceptually plausible, though its general acceptance as an explanation for the origin of life requires further evidence.
See : Wikipedia