≥3.5–3.7 Billion years old
||Weinbauer MG. Ecology of prokaryotic viruses. FEMS Microbiol Rev. 2004 May28(2):127-81. p.138 left column 2nd paragraphPubMed ID15109783
||Ackermann HW. Tailed bacteriophages: the order caudovirales. Adv Virus Res. 1998 51: 135-201. Review.PubMed ID9891587
||"The origin of tailed phages occurred before the
separation of life into the three domains Bacteria,
Archaea and Eukarya, and tailed phages are probably at
least 3.5–3.7 billion years old [primary source]."