Classicly

Downey's mind reeled. An explanation, amazing and yet barely possible, had flashed over him. What if the impact of the explosion had sealed both ends of the concrete tube where he and Judith had sought refuge? What if the tube had been buried beneath the earth, to remain there for centuries? What if the poison gas released by the bombs had entered their retreat, too diluted to kill them and yet strong enough to produce suspended animation?

He remembered reading of a new war gas which could cause precisely that effect; and he knew that such substances did exist in nature: as, for example, the paralyzing fluid which the hunting wasp injects into the spider, to keep it indefinitely alive though seemingly lifeless. If such a poison could operate for weeks or months, what was there to prevent it from being effective for a year? for ten years? even for three hundred years?