Donno about dusty rock as water has been here in liquid form for quite a long time and many theories of the origins of life here posit that it started in water. As to virus though, I think you may be mean parasite because we humans surely are symbiant creatures. The web of life is intricate, we are part of many food chains, we create new food chains and destroy entire species, we make new mountains, islands, deserts, and other land forms as well as new plants, bacterias, viruses, animals, vegetables, and minerals... I'm very lucky to have been in the presence of the creation of amino acids, (basic building blocks of life), by electro-chemical stimulation of inert molecules - now that's a trippy thing!