We tend to think of ourselves as surface dwellers, roaming about on the surface of Earth, far beneath the inhospitable emptiness of space. There are blue skies above us and life-sustaining air all around. It seems so light, this atmosphere of ours, that we hardly give it any thought. Indeed, unless it threatens us with disastrous weather, we take it largely for granted. But air is not as light and insubstantial as it seems, nor is the dangerous radioactivity of space all that far away.  More than 99% of the air in our atmosphere is within only 100 Km of the surface. 

As Gabrielle Walker reminds us in her new book, An Ocean of Air: Why the Wind Blows and Other Mysteries of the Atmosphere, we live, thankfully, at the very bottom of this ocean of air. In this beautiful and eminently readable book, Walker tells us the story of air and how it transformed Earth long ago to make it hospitable to larger life forms, including ourselves, but also how it continues to protect us from the dangers of space and now must be protected by us.

Gabrielle Walker is a freelance writer, broadcaster, and speaker specializing in science and technology, with particular emphasis on energy and climate change. She has been an editor at Nature and Features Editor at New Scientist, for whom she now acts as consultant. She has a doctorate in chemistry, has written, broadcast, and lectured widely on science and policy issues, and has been a visiting professor at Princeton University. Her first book was Snowball Earth, the story of Paul Hoffman's quest to prove that the Cambrian Explosion, the moment in geological time when multifarious complex life forms first emerged, resulted from a cataclysmic explosion some 700 million years ago. An Ocean of Air is her second book.

An Ocean of Air opens with the story of Captain Joseph W. Kittinger, a test pilot for the U.S. Air Force, "the man who fell to Earth and lived." Walker throws her readers right into the story of air by taking us twenty miles up into the atmosphere, a place with air so thin we couldn't possibly survive without the protection of a pressure suit. Instruction begins immediately. We observe, with Kittinger, the thin blue line that "has transformed our planet from a barren lump of rock into a world full of life... the only shield that stands between vulnerable earthlings and the deadly environment of space." As he steps off the platform of the gondola hanging beneath a giant helium balloon, we plunge with him through the layers of air at close to the speed of sound. We learn, as he falls, about solar wind channeled away from Earth by its magnetic field, lethal x-rays intercepted and absorbed by the ionosphere, dangerous ultraviolet rays soaked up and diffused by ozone, and about the troposphere, that "thick, life-giving blanket of air, wind, and weather that turns our planet into home." Sounds like an action hero story.