Viruses are Earth’s most abundant biological entities

Viruses are considered Earth’s most abundant biological entities; a rough estimate of about 10³¹ viral particles is often cited. This is not a precise census: recent reviews stress substantial uncertainty and suggest the estimate may be revised downward toward 10³⁰. Calling viruses a “form of life” depends on the definition: they evolve and reproduce in host cells, but lack independent metabolism outside cells, so their status as living organisms remains debated.