About 3.7 billion years ago, RNA virus ancestors may trace back to the RNA world, but we can’t prove whether they predate LUCA or arose just after. 

About 2.75 billion years ago, the Varidnaviria evolved a unique “Double Jelly-Roll” protein fold to build massive, diverse shells, allowing viruses to scale up from tiny parasites to “giant” viruses that mimic cells.

About 1.25 billion years ago, Retroviruses emerged by transforming “jumping genes” into infectious agents, mastering the ability to rewrite a host’s permanent genetic code.

Around the time of the first bacteria, about 3.2 billion years ago and after LUCA, the Duplodnaviria evolved a high-pressure, icosahedral protein armor that turned viruses into biological syringes capable of injecting DNA into any domain of life.

About 1.75 billion years ago, Monodnaviria evolved as “runaway” genetic loops (plasmids) that stole structural proteins from other viruses to become independent, single-stranded DNA parasites.

About 1 billion years ago, giant viruses evolved by “hoarding” cellular genes, expanding their genomes until they blurred the line between a simple virus and a living cell.