Let’s break down the structure of The Green Rain to see how it works as a piece of science fiction and a piece of social commentary:
Inciting incident: a rocket containing a chemical called chlorophylogen, intended to terraform the moon, crashes back to earth, burning up in the earth’s atmosphere.
Results: a third of the world’s population is transformed into “green” men, REGARDLESS of their original color. Any women so transformed will give birth to infants similarly colored. In time, the whole world will become green.
Social efforts to deal with this transformation: attempts to identify “inferior” races to keep them from taking advantage of their newfound ability to conceal their former social caste, including birth-certificate registration, physical markings, etc. Some countries suggest destroying “greens” as Nazis liquidated unwanted races during WWII (viz., through death camps).
Attempts to bring “harmony” back to the world: scientific experiments to trigger color changes (going from white to green, from green to white, etc.), which ultimately lead to a second rocket being launched into the atmosphere, bringing a second green rain to earth.
Tipping-point saturation: 1930s science suggested that poisons could accumulate in a living organism, seemingly harmlessly for years, only to reach a critical point, or an event horizon, where they ceased to harmless. A man who has worked with lead paint for years suddenly develops wrist drop, etc. In this case, the earth reaches its own saturation point, where the cholorphylogen ceases to be an inert chemical and does what it was designed to do from the start–terraform.
Initial outcome: those who come out for the second green rain (practically the whole world, minus communist countries who contain their citizens in their homes by gunpoint). The color change goes off without a hitch.
Story twist: The genetic plan of earth plants is altered to encourage out-of-control growth. Nothing can contain the plants, short of complete darkness. Containment attempts include firing the plants (fails), capping the plants (eventually fails), and hiding in absolute darkness (ultimately fails). The plants begin to consume oxygen at an alarming rate, while leaving carbon dioxide in the air, making the atmosphere ultimately unbreathable for humans.
Final twist: astronauts on the moon watch as the entire earth turns into one green ball.
“The tape ran on silently until it came to the end of the spool. Pelargus (scientist) was leaning back, his eyes closed, his large, bony hands on his knees. And, with soft tapping, gentle scraping, with undulations and sinuous obeisances, the green tomb-builders and enshriners came to erect his mausoleum and make him part of their greenness.”by