Something happened to the Earth about 600 million years ago, something that produced an explosion of life and led to the variety of multi-celled forms that we see today. Before that, for nearly 4 billion years, life consisted of single-celled slime.
A minority of geophysicists believe the transformation occurred because the surface of the Earth first froze completely, with ice even at the tropics, and was then subjected to a runaway greenhouse effect that melted the ice. The associated stresses, it is argued, acted as a spur to evolution and set rolling the ball that would lead to us.
This is a story worth telling, even if the scientific evidence in favour is at best incomplete. The British science writer Gabrielle Walker is an ideal person to tell it, being an enthusiast for the idea, although at one point even she admits that she is describing "speculation heaped on speculation". The case is not helped by comparing the reception given to "Snowball Earth" with that given to Alfred Wegener's ideas about continental drift. Far better to have stuck to the theme that controversial ideas in science are always valuable if they provoke new research.
The style Walker has chosen matches her subject, being racy and pacey, with a focus on the people involved rather than the science (a good idea, since there isn't much science). We learn about life in the field in the deserts of Namibia and other exotic locations; we meet, among others, a geophysicist who could have been a world-class marathon runner but decided he wasn't quite good enough for Olympic gold; and we get plenty of scientific feuding (one chapter is entitled "Snowbrawls").
This is a style associated with a certain kind of American journalism, and not one that I usually enjoy, but it does work here. Even so, it is hard to suppress the gagging reflex when confronted with passages such as this: "She was 28 years old, plump, pretty, with neatly manicured fingernails, tiny silver hoops in her ears, soft brown hair cut and flicked into symmetrical waves that framed her face."
What about the science? When Walker chooses (too rarely, for my taste), she shows she can be equally lyrical about that: "At one abrupt moment roughly 600 million years ago, something shook the Earth out of its complacency. From this came the beginnings of eyes, teeth, legs, wings, feathers, hair and brains. Every insect, every ape and antelope, every fish, bird and worm. Whatever triggered this new beginning was ultimately responsible for the existence of you and everyone you've ever known."
Was that trigger global ice? The biggest flaw with the idea is that there is no accepted explanation for how and why the planet could have frozen in the first place. This is also, inevitably, the biggest flaw with the story Walker has to tell, and the problem is not one she confronts. She does, however, offer a very entertaining read, the scientific equivalent of those novels that involve a lot of sex and shopping. Ideal to read on a journey or on the beach, Snowball Earth will probably be a bestseller – at least in the US.
John Gribbin's latest book is 'Science: a history', published by Penguin