Against this attack the various camps of Minervaists concluded a hasty alliance and opened counterfire with calculations of their own, which invoked the greenhouse effect of atmospheric carbon dioxide to show that a substantially higher temperature could have been sustained. They demonstrated further that the percentage of carbon dioxide required to produce the mean temperature that they had already estimated by other means, was precisely the figure arrived at by Professor Schorn in his deduction of the composition of the Minervan atmosphere from an analysis of Charlie's cell metabolism and respiratory system. The land mine that finally demolished the Pure Earthist position was Schorn's later pronouncement that Charlie exhibited several physiological signs implying adaptation to an abnormally high level of carbon dioxide.

Their curiosity stimulated by all this sudden interest in the amount of carbon dioxide in the Minervan atmosphere, Hunt and Danchekker devised a separate experiment of their own. Combining Hunt's mathematical skill with Danchekker's knowledge of quantitive molecular biology, they developed a computer model of generalized Minervan microchemical behavior potentials, based on data derived from the native fish. It took them over three months to perfect. Then they applied to the model a series of mathematical operators that simulated the effects of different chemical agents in the environment. When he viewed the results on the screen in one of the console rooms Danchekker's conclusion was quite definite: "Any air-breathing life form that evolved from the same primitive ancestors as this fish and inherited the same fundamental system of microchemistry, would be extremely susceptible to a family of toxins that includes carbon dioxide—far more so than the majority of terrestrial species."

For once, everything added up. About twenty-five million years ago, the concentration of carbon dioxide in the atmosphere of Minerva apparently increased suddenly, possibly through some natural cause that had liberated the gas from chemical combination in rocks, or possibly as a result of something the Ganymeans had done. This could also explain why the Ganymeans had brought in all the animals. Perhaps their prime objective had been to redress the balance by covering the planet with carbon-dioxide-absorbing, oxygen-producing terrestrial green plants; the animals had been included simply to preserve a balanced ecology in which the plants could survive. The attempt failed. The native life succumbed, and the more highly resistant immigrants flourished and spread out over a whole new world denuded of alien competition. Nobody knew for sure that it had been so on Minerva. Possibly nobody ever would.