Financial Times, 16th November 2002
Jerome Burne is impressed by a highly ambitious piece of scientific polemic on the life-and-death powers of oxygen in Oxygen: The Molecule that Made the World by Nick Lane.
The dust jacket shows a sepia photograph of a fossilised dragonfly, which, we learn inside, is a mysterious and beautiful example of the intimate relationship between life, death and oxygen. The giant Bolsover dragonfly flew through the great forests of the Carboniferous period some 300 million years ago. It had a huge, 20-inch wingspan, and the mystery is how it ever managed to stay aloft.
Insects don’t breathe like we do. They absorb the oxygen they need through pores along their body. This limits their size because the volume of oxygen reaching their muscles depends on the proportion of the gas in the atmosphere. So some scientists have suggested that the atmosphere in those times was richer in oxygen than now.
Critics swiftly pointed out the flaw in this theory. Oxygen releases its energy easily, which is why it is vital for combustion, but a higher concentration would rapidly turn the earth into a fireball. A single lightning strike could ignite a rainforest, consuming giant dragonflies, 3-ft scorpions and all.
Nick Lane marshals an impressive array of evidence – from the mechanics of insect flight to the levels of carbon 13 in rocks – to suggest that the ancient atmosphere may indeed have been oxygen-rich after all. But an explanation for the giant forests and creatures of the Carboniferous age is only a single part of this ambitious narrative. Oxygen is a piece of radical scientific polemic, nothing less than a total rethink of how life evolved between about 3.5 billion and 543 million years ago, and how that relates to the diseases we suffer from today.
The whole picture is bound together by the Janus-faced, life-and-death powers of oxygen. For those not up to speed on their chemistry, oxygen is vital to the metabolism of plants and animals because plants use sunlight to split water, releasing energy to manufacture carbohydrates from carbon and expelling oxygen as waste. We reverse the process, using the energy from splitting oxygen to burn fats and carbohydrates, while giving off carbon dioxide and water.
But oxygen has a dark side too, and it is this that drives both Lane’s narrative and the evolution of life itself. The same chemical reactions are involved in going from water to oxygen and vice versa. What’s not widely appreciated is that atomic radiation also works by splitting water, using x-rays or gamma rays rather than sunlight. “In both nuclear power and oxygen driven photosynthesis,” writes Lane, “the safety margins are slim but the potential benefits of unlimited power are huge.”
Whichever direction the reaction is going – water to oxygen or back – the dangers are the same. This process, oxidization, produces free radicals – highly reactive molecules that strip electrons from any surrounding material. The most visible example is the rusting of iron, but when fats, like butter, go rancid the same thing is happening. So for living things to harness the power of oxygen, they have to be able to cage it and neutralise the free radicals with antioxidants. In mammals the best known of these are probably vitamins C and E.
But how did oxygen become incorporated into the process of life to begin with? Mastering the trick of splitting water gives you unlimited power, but it is also suicidal without a ready supply of protective antioxidants. However, the text books tell us that free oxygen didn’t appear in the earth’s atmosphere until about 2.5 billion years ago when the first “cyanobacteria” emerged, which had learnt how to split water to produce oxygen and hydrogen. So how did early life evolve a protection against something before it appeared in the environment?
Lane produces long but lucid chains of evidence, drawing on the latest research, to suggest that the earliest life form – known as Luca (Last Universal Common Ancestor) had actually developed a type of antioxidant. He goes on to trace how the complex and dynamic interactions between the emerging life forms and geology eventually produced a surge of oxygen in the atmosphere around 543 million years ago.
This was the Cambrian Explosion – when new and varied forms of life suddenly appeared in the fossil record. Exactly why has long been hotly debated. Lane again puts together an impressive case to suggest that the rise of available oxygen not only gave evolution a massive boost, but also allowed the first predators to emerge.
All this is fascinating, but perhaps the book’s most remarkable achievement is to demonstrate a direct connection between the Faustian pact that Luca made with oxygen 3.5 million years ago and the diseases of aging that we suffer from today. The link allows Lane to turn some more conventional wisdom on its head. For instance, he devotes a chapter to his grave doubts about the value of taking antioxidant supplements, and explains why contracting malaria may protect you against arthritis. This is science writing at its best.