Shilohin paused a moment, waiting for that much to sink in. Then she continued. “The average concentration of radioactive, heat-producing substances in Minervan rocks was somewhat higher than is found on Earth. The interior of Minerva was thus
hotter and molten to a greater degree, and the crust was thinner. The planet was therefore more active volcanically than Earth, a tendency that was further complicated by the strong tidal forces induced in the crust by Luna, which orbited closer to Minerva than it does to Earth today. This high level of volcanic activity released large quantities of carbon dioxide and water vapor into the atmosphere, resulting in a greenhouse effect that sustained a high enough surface temperature for the oceans to remain liquid and life to emerge. By terrestrial standards it was still sure-as-hell cold, but not nearly as cold as it would have been otherwise.
“This situation had always existed throughout the history of Minerva. By the time that our civilization was at its peak, however, a new epoch of tectonic activity was just beginning. The level of carbon dioxide in the atmosphere began showing a measurable increase. It soon became clear that it would only be a matter of time before the level grew beyond the point we could tolerate. After that our world would become, for us, uninhabitable. What could we do?” Shilohin let the question hang and cast her eyes around the room, apparently inviting the Earthmen to start a discussion.
After a few seconds a UNSA engineer at the back responded. “Well, we’ve seen some pretty remarkable examples of the kind of technology that you people had. I wouldn’t have thought you’d have found it much of a problem to figure out some way of simply winding the level back down again . . . some kinda planetwide climatic control, I guess. . . sump’n like that.”
“Commendably on the ball,” she said, with something that they took to be the equivalent of an approving nod. “We did in fact employ planetary climatic control to some degree, primarily to limit the extent of the Minervan ice caps. But when it came to tinkering with the chemical composition of the atmosphere, we were less certain of our ability to keep everything sufficiently under control; the balance was very delicate.” She looked directly at the questioner. “A scheme along the lines you suggest was in fact proposed, but mathematical models indicated that there was too high a risk of destroying the greenhouse effect completely, and so of guaranteeing the end of life on Minerva even more quickly. We are a cautious people and do not take risks readily. Our government threw the idea out.”
She remained silent and allowed them time to think of other
possibilities. Danchekker didn’t bother to raise the notion that they might have tried importing terrestrial plant life as an attempt at introducing a compensatory mechanism. He already knew full well that the Ganymeans knew nothing of such a venture. Presumably that solution had been tried after Garuth’s expedition had departed. Further analyses by his scientists and discussions with ZORAC had indicated if that had been the objective of the exercise, it would not have succeeded anyway-a point that would surely not have escaped the Ganymean scientists at the time. For the moment this event was still as much a mystery as ever.
Eventually Shilohin spread her arm wide as if appealing to a class of children who were being a little slow that day. “Logically it’s very simple,” she said. “If we left the carbon-dioxide level to rise, we would die. Therefore we could not allow it to rise. If we prevented the rise, as we could have done, there would have been too much of a risk of freezing the whole planet solid because the carbon dioxide kept Minerva warm through the greenhouse effect. We needed the results of the greenhouse effect to keep us warm because we were a long way from the Sun. Hence, we wouldn’t need it at all if we were nearer the Sun, or if the Sun were warmer.”
Some of the faces in front of her remained blank; some suddenly looked incredulous. “It’s easy then,” a voice called from near Hunt. “All you had to do was move Minerva in a bit or heat up the Sun.” He meant that as a joke but the Ganymean began nodding her head in imitation of the human mannerism.