It happens that I am not persuaded, even though I share Davies’s doubts about the primordial soup. This is because I find the evidence for a cosmic origin of life, in the clouds of material between the stars, even more compelling (largely because of the immense amount of time offered by this scenario for life to emerge).The cosmic connection has been promoted by another eminent astronomer, Sir Fred Hoyle, who has unfortunately tended to antagonise his critics by seeming to stray across the fine line separating respectable speculation from cranky theorising. But science usually makes rapid progress when two (or more) rival hypotheses purport to explain the same phenomenon, and we now have the delicious prospect of a rivalry between the Deep Earthers and the Cosmic Connectors which will stimulate the debate about how and where life first appeared.I don’t by any means agree with all conclusions Davies reaches in this delightful book. To his credit, Davies also discusses these ideas, explaining why he is dissatisfied with them on scientific grounds.

J B S Haldane elaborated this idea to encompass the entire primordial ocean, in a condition he memorably described as having “the consistency of hot dilute soup”. Davies clearly spells out the problems with the primordial soup hypothesis, before offering his alternative.The argument is beautifully constructed, and quite persuasive. He prepares the ground so that his dramatic suggestion that life began “hot and deep” – far below the surface of the young Earth, where it was protected from the battering that took place at the planet’s surface as debris from the formation of the solar system rained down – seems both natural and compelling.The key step in this preparation involves a thorough discussion of the difficulties of the conventional view: that life on Earth originated in what Charles Darwin called a “warm little pond” at the surface of the planet. Rather, after introducing the idea of the relationship between life and thermodynamics, Davies sidles round the back of his main theme, introducing us to the genetic code and to traditional ideas about the origin of life. They feed off the entropy flow associated with underwater volcanic vents, and off other superbugs that seem to exist deep within the “solid” Earth (actually, honeycombed with microscopic pores).

Their existence is revealed by, among other things, the deep-drilling programmes of the oil explorers.But perhaps “pounces” is the wrong word. Life on Earth today exists because the Sun is hot and the surface of the Earth is cool. The shift of energy from the Sun to the Earth implies that the thermodynamic quantity known as entropy, which is inversely related to the existence of complexity and information, can decrease on the surface of the Earth even though it always increases in the universe at large. Interesting things can happen on the surface of the Earth because elsewhere things are getting more and more boring as the stars die. Eventually, the Sun will be a burnt-out cinder at the same temperature as its surroundings.Using this kind of physical insight, Davies pounces on the recent discovery of bacteria that live in the depths of the ocean. He also uses his writing skills to bring a fascinating but largely unsung idea into the limelight.
The theme of The Fifth Miracle is not so much how life came into being, or even what life is (although Davies offers as neat a summary of its meaning as you could hope to see), but rather where life can exist – in particular, where life can originate.The key to life, at this level, is a flow of energy from a hotter system to a cooler one. But Davies succeeds not only in being provocative and controversial, but in maintaining the rigorous scientific approach of the physicist.