Was it possible to feel nostalgic about something that had never happened to him, possible for nostalgia to be taken in by the body as a free pathogen to infect the consciousness with stray sentiments? Perhaps, in his dreams, he had traveled back in time, or even drifted into another dimension of space-time and inhabited the body, experiences, and nostalgia of another. To even envisage so allowed the trauma of those lost moments, though not his own, to draw from him a certain envy for the entity in whose memories he had basked vicariously. . .Perhaps, nostalgia was a microorganism. . .the bacterium that infected. . . Yes. . .maybe he was sick.

...the life of the planet began the long, slow process of modulating and regulating the physical conditions of the planet. The oxygen in today's atmosphere is almost entirely the result of photosynthetic living, which had its start with the appearance of blue-green algae among the microorganisms.