"Those," said he, "are speculations too high, problems really insoluble. Do not let us enter into them. Let us only admit the insufficiency of primordial attraction, and then by the inequality of rotation and revolution days and nights could succeed each other upon the moon as they do upon the earth. Besides, even under those conditions life was possible."
"Then," asked Michel Ardan, "humanity has quite disappeared from the moon?"
"Yes," answered Barbicane, "after having, doubtless, existed for thousands of centuries. Then gradually the atmosphere becoming rarefied, the disc will again be uninhabitable like the terrestrial globe will one day become by cooling."
"By cooling?"
"Certainly," answered Barbicane. "As the interior fires became extinguished the incandescent matter was concentrated and the lunar disc became cool. By degrees the consequences of this phenomenon came about—the disappearance of organic beings and the disappearance of vegetation. Soon the atmosphere became rarefied, and was probably drawn away by terrestrial attraction; the breathable air disappeared, and so did water by evaporation. At that epoch the moon became uninhabitable, and was no longer inhabited. It was a dead world like it is to-day."
"And you say that the like fate is reserved for the earth?"
"Very probably."
"But when?"
"When the cooling of its crust will have made it uninhabitable."
"Has the time it will take our unfortunate globe to melt been calculated?"