In a real sense on Earth, the beginning of all modern cellular life is LUCA, which diverged into bacteria and archaea. Viruses, in contrast, represent multiple ancient inventions of parasitic replication layered over billions of years. Not quite life, some viral lineages may be nearly as old as cells, while others are evolutionary latecomers. Viruses are not one lineage — they are recurring evolutionary solutions.

Pre-LUCA Genetic Jungle: RNA Replicators and Early Virus-Like Entities.
LUCA lived about 3.75 bya
Virus Evolution Fuzzily Starts 3.7 bya

Virus: Riboviria (Early RNA replicators)

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.

~3.7 Billion Years Ago (+/- 100 million)

Bacteriophage → Duplodnaviria

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

~3.2 Billion Years Ago (+/- 200 million)

The HK97-Fold (Steel Pouch)

Virus: Varidnaviria

~2.75 Billion years ago (+/- 200 million)

double jelly-roll capsid DNA viruses

Monodnaviria

~1.75 Billion years ago (+/- 200 million)

single-stranded DNA viruses

Retroviruses (within Riboviria)

~1.25 Billion years ago (+/- 200 million)

Stitch themselves permanently into the host’s genome

Giant viruses (within Varidnaviria)

About 15 million ordinary viruses could hide inside the period at the end of this sentence. A billion years ago, some viruses turned into genetic junkyard collectors and swelled to nearly a micrometer across. Only 150,000 of these giants would fit inside that same dot — about ten times wider, and nearly a thousand times more massive, than the common viruses of today.

~1 Billion years ago (+/- 200 million)

Extreme genetic theft