The carbon dioxide brought him up sharp.
If there had been life here once, there would have been plant life as well, and therefore oxygen. If the war had been so long ago that the free oxygen had since gone out of the atmosphere—good God, how old were the robots? Steffens looked at Ball, then at the silent robots, then out across the field to where the rest of them stood. The black wheat. Steffens felt a deep chill.
Were they immortal?
"Would you like to see a doctor?"
Steffens jumped at the familiar words, then realized to what the robot was referring.
"No, not yet," he said, "thank you." He swallowed hard as the robots continued waiting patiently.
"Could you tell me," he said at last, "how old you are? Individually?"
"By your reckoning," said his robot, and paused to make the calculation, "I am forty-four years, seven months, and eighteen days of age, with ten years and approximately nine months yet to be alive."
Steffens tried to understand that.