They tell him to watch the pillar of light. At first there is no change, but in a moment the light itself begins to roil and thicken—like quicksilver mixing with smoke—and then a scene takes form in the light. It is a view of dense primordial jungle, blazing under a young sun. Then there is a crashing through the jungle, and the Earthmen reel back in astonishment as the behemoth bulk of a giant wooly mammoth bursts out of the foliage.

They show him the time of the Mastodons; the time of the Clipper Ships; the time of the Depression, 1930. And the men of Earth marvel.

As we HOLD PAST BECKWITH in F.G. to the Earthmen watching the pillar of light, we HEAR Kirk ask if it is possible to go back in time, back to, say, Old Earth. The Guardians indicate it is possible.

But it is not wise. Man and non-Man must live in their present or their future. But never in their past, save to learn lessons from it. Time can be dangerous. If passage back is effected, the voyager may add a new factor to the past, and thus alter everything from that point to the present, all through the universe. Time is elastic. It has a tendency to revert to its original shape when the changes are minor. But when the change is life or death…when the sum of intelligence has been altered then the change can be permanent…and cataclysmic. So we do not go back. For one hundred thousand years no one has gone back.

The time vortex has been left set at the year 1930, Old Earth. As Kirk and Spock talk with the Guardians, the ancient men tell them that time moves at its normal pace all through the universe, but not here, not within the sphere of influence of the machine, for it is akin to standing on the king’s cross, a zone of no-time. And that explains why there is atmosphere and warmth on this dead world. If they can control time, how much simpler it is to control their environment. It also explains the radiations received by the Enterprise, the radiations that caused their chronometers to go berserk. Spock then says to Kirk, “You see how old they are, centuries older than any human or alien we have ever encountered? Yet they say that time moves barely at all here. Can you imagine how old they must be to have aged so much.”