An Ocean of Air by Gabrielle Walker

We humans tend to go about our daily lives more or less ignoring the fact that there are hundreds of kilometres of air above our heads which serve the dual purpose of being a life-giving force and a protective blanket against the worst deadly rays space can throw at us. In an effort to combat this narrow viewpoint, Gabrielle Walker has produced athoroughly readable and engaging natural history of the atmosphere, discussing every aspect of the sky above and the air around us in authoritative but never overbearing style.

Astunning prologue recounts the highest skydive ever made. In 1960, Joe Kittinger stepped from a balloon floating 32 kilometres above New Mexico and proceeded to plummet through the different layers of the atmosphere for several minutes before opening his parachute and landing intact - a feat never since repeated, presumably because it's a little bit insane.

Walker breathlessly ties in the scientific drama of what's happening in the air around Kittinger with the tumbling descent of the man himself. As an opening to a popular science book, it's exhilarating, and if the rest of An Ocean of Air perhaps fails to live up to that visceral ride, it's nevertheless an enjoyable journey in its own, more sedate, way.

The first half of the book deals primarily with the lower levels of the atmosphere, and the discoveries of its constituents and characteristics over the centuries. Much of these early sections are, by necessity, something like a lesson in the history of atmospheric science, chemistry in particular, but Walker is adept at organising her research into digestible nuggets of information. She also has a handy knack of bringing her historical characters to life on the page.

We start with Galileo devising experiments late in life to measure the weight of air, and over the next three chapters we leap around the centuries as "natural philosophers" gradually discovered the constituent parts of the air we breathe, as well as their properties. Oxygen is revealed as an elixir of life on the planet, while carbon dioxide provides invaluable food and warmth for that life.

Around the middle of An Ocean of Air, the author's normally clear and concise prose briefly lets her down. In attempting to explain the physics behind the easterly Trade winds and the prevailing Westerlies further from the equator, Walker gets bogged down in the science. There are occasional impenetrable passages, and you can't help feeling that a few more diagrams would have clarified matters. But that small quibble aside, Walker's pellucid style is a delight to read, especially in the later chapters, where she deals with the extraordinary outer layers of the atmosphere: the ozone layer, the ionosphere and the radioactive magnetic fields of the van Allen belt.

All three regions serve to protect life on earth, the ozone layer filtering out deadly ultra-violet rays, the ionosphere handling X-rays while the van Allen belt intercepts cosmic rays. Much of the science behind these outer layers is a long way from being completely understood, but Walker treads the line between layperson's knowledge and complex science with skill and balance.

As we sit with the frantic wireless operator onboard the doomed Titanic, or hunch against the cold in the frozen Norwegian wastelands with scientists measuring the aurora borealis for the first time, An Ocean of Air is more like an exhilarating adventure tale than a popular science book. It's unlikely you'll ever look up at the sky in quite the same way again.