RNA FIRST WORLD. ” The emergence of DNA in the RNA world: an in silico simulation study of genetic takeover. It is now popularly accepted that there was an “RNA world” in early evolution of life. This idea has a direct consequence that later on there should have been a takeover of genetic material – RNA by DNA.”
http://bmcevolbiol.biomedcentral.com/articles/10.1186/s12862-015-0548-1