Man-made perils to the universe’s garden of life are evident from space.

In 1961, Yuri A. Gagarin, the first man to orbit the Earth, issued his initial impressions from an altitude of more than 100 miles. The sky was deep black, he said, and the Earth’s horizon crowned with “a beautiful blue halo.” Between bright white clouds, he enthused, he could make out “snow, forest, mountains.” It was an Edenic picture.

In the subsequent depths of the cold war, with nuclear weapons racing off the assembly lines of the Soviet Union and the United States, succeeding cosmonauts and astronauts contributed their own observations. Like Mr. Gagarin, they found their world mesmerizingly beautiful. They also reported a singularly intriguing fact: no borders or political boundaries could be seen from space.

In fact, few signs of humanity were visible, at least on the sunlit side. Sure, Los Angeles was visibly smoggy. And irrigated cropland could sometimes be discerned, like pointillism on Nile Delta sand. But these were exceptions. Under a startlingly thin layer of atmosphere, vast expanses of desert ceded to forests that gave way to the oceans that make up 70 percent of Earth’s surface. The planet seemed largely untouched. Only at night, when jewel-like cities rotated into view, did clear signs of civilization emerge.

There was something profoundly reassuring about this. Even as the ICBMs slept, it was heartening to know that despite our best efforts, we had not yet banged up the biosphere enough to make the effects easily visible from space.