According to their measurements, the result was a nearly perfect reproduction of Old Earth’s atmosphere. No one who breathed it after a lifetime spent in habitats needed scientific data to back that up. Its smell penetrated to some ancient part of the brain, triggering instincts that must go all the way back to hominid ancestors living on the shores of Africa millions of years ago. As she knew from having traveled to Earth many times, it was a kind of intoxicant. It was the best drug in the universe. It made people want to be on Earth more than anything. It was the reason that Cradle—which was bathed in that air, being dragged through it all the time on the end of its thirty-six-thousand-kilometer string—was the most exclusive community in existence. And it was the reason that Red and Blue had twice gone to war over the right to live on the surface.