He meant to pull his arms through at once, after resting for just a moment, but as he rested, panting from the exertion, he realized that his need to breathe only increased, and was growing desperate. He was suffocating somehow, even as he drew great draughts of strange-smelling air into his lungs.
Strange-smelling air, dry and cool, and he wasn't getting any oxygen. Even as the panic of suffocation rose within him, his rational mind realized what he should have known all along: The reason that nothing lived behind the barrier was that there was no oxygen in here. It was a place designed to eliminate all decay - and most decay, the rapidest of it, was linked to the presence of oxygen, or oxygen and hydrogen joined to form water. There could be no life, and therefore not even microbes to eat away at surfaces; no water to condense or freeze or flow; no oxidation of metals. And if the atmosphere also failed to support anaerobic life-forms, there'd be little within the barrier to cause decay except sunlight, cosmic radiation, and atomic decay. The barrier had been set up to preserve everything within it, so it could last for forty million years.
This sudden comprehension of the purpose of the barrier was no comfort. For his rational mind was not particularly in control right now. No sooner had he realized that he could not breathe than his hands, still sticking through the barrier, began clutching for air, trying to pull him back through the barrier. But he was in exactly the same situation he had been in before, on the outside, when only an arm was through the wall. He could push his arms deeper into the barrier, but when his face and chest reached the wall, he could go no farther. His hands could touch the breathable air on the other side, but that was all.
Made savage by fear, he beat his head against the barrier, but there simply wasn't leverage - even with panic driving his muscles - to get force enough to push his face through to the breathable air. He really was going to die. Yet he still struck his head against the barrier, again, again, harder.
Perhaps with the last blow he stunned himself; perhaps he was simply weakening from lack of oxygen, or merely losing his balance. Whatever happened, he fell backward, the resistance of the barrier slowing his fall as his arms slipped inside through the invisible wall.
This is fine, thought Nafai. If I can just get to where the slope goes the other way, I can run down toward the barrier and get through again, only this time face first. Even as he thought of this cheerful plan, he knew it wouldn't work. He had spent too long already trying to get through the barrier right here - he had used up too much oxygen inside his own body, and there was no way he had enough left to climb another hill and make another downward run before he blacked out.
His hands came free and he fell backward onto the stony ground.
He must have struck very hard, for to him it sounded like the loudest, longest thunderclap he had ever heard. And then wind tore across his body, picking him up, rolling him, twisting him.
As he gasped in the wind, he could feel that somehow, miraculously, his breathing was working again. He was getting oxygen. He was also getting bruised as the wind tossed him here and there. On the stones. On the grass.
On the grass.
The wind had died down to a gusty breeze - he opened his eyes. He had been flung every which way, perhaps fifty yards. It took him a while to orient himself. But, lying on grass, he knew he was outside the barrier. Was the wind another defense mechanism, then, hurling intruders through the wall? Certainly his body was scraped and bruised enough to bear that interpretation. He could still see a few dust devils whirling in the distance, far within the dead land.
He got up and walked to the barrier. He reached out for it, but it wasn't there. The barrier was gone.
That was the cause of the wind. Atmospheres that had not mixed in forty million years had suddenly combined again, and the pressure must not have been equal on both sides of the barrier. It was like a balloon popping, and he had been tossed about like a scrap of the balloon's skin.