For something like two hundred million R-years this state of affairs continued. Just as the previous, pre-irradiation characteristics seemed to be stable, if not permanent, so, now, did it seem that this pestilential place full of gigantic and savage animals would remain as it was. There then occurred, unexpectedly, the second burst of radiation.

The effects were again dramatic.

There was every kind of cataclysm and upheaval. Land sank beneath the water and became ocean bed; new land appeared from the seas, and for the first time there was high terrain and mountains. Volcanic activity had never been absent, since the crust covering the still molten core was so thin, but now land and water were continuously convulsed. The mantle of cloud that had Sometimes kept the whole planet in warm gloom for weeks at a time was rent tumultuously with storms and winds.

All the large species were destroyed. The great lizards were no more to be seen, and the forests of giant ferns were laid flat by the violent winds and rain.

There was a sudden cooling. When the convulsions lessened, and ceased, the planet was left transformed. In a very short time, much of the water was massed around the poles in the form of ice and snow. Some swampy areas remained but now earth and oceans were separated, and there were areas of dry land. That was of course long before the planet’s axis had been knocked out of the vertical: before the “seasons” that contributed so much to its instability. The poles were cold. The area around the middle was hot. In between were zones of predictable and steadily temperate climate.

This was period (3), from which both Canopus and ourselves hoped so much, when conditions were as perfect as can be expected on any planet—and which was to last rather less than twenty thousand R-years.