Aliens: The World's Leading Scientists on the Search for Extraterrestrial Life by Jim Al-Khalili

Author:Jim Al-Khalili [Al-Khalili, Jim]
Language: eng
Format: azw3, epub
Publisher: Picador
Published: 2017-05-09T04:00:00+00:00

11

Electric Origins in Deep-Sea Vents: How Life Got Started on Earth

Nick Lane

‘I can’t define it, but I know it when I see it,’ said US Supreme Court Justice Potter Stewart, on the subject of hardcore pornography. He could have been speaking about life itself, which is, if anything, even more difficult to define. Could a wild fire, for example, be considered alive? Plainly not, although it satisfies some of the standard criteria, such as ‘feeding’, ‘growth’ and ‘reproduction’, as for that matter do growing crystals. We ‘know’ they are not alive, but we are hard put to come up with a strict definition that excludes them. The opposite applies to viruses. They look like tiny machines, as carefully designed to carry out their task as a lunar landing module. The way they take over the machinery of cells to turn out thousands of copies of themselves is hard not to describe as purposeful. Design, purpose: these are loaded words but they can hardly be ascribed to an inanimate force. Yet viruses lack their own metabolism – they are strictly inanimate – and so are excluded from many definitions of life.

Let’s put aside even more equivocal cases such as computer programs, and simply acknowledge that life is hard to define. Does that make studying the origin of life a problem? Yes, insofar as there is no agreement about what exactly we are trying to explain, and, equally, what might constitute life on other planets. No, insofar as the very many steps en route to the first living cells form a continuum: there is no single point at which we can unequivocally say that a complex molecular system is all-of-a-sudden alive. The earliest steps on this continuum were certainly not alive. So what exactly were they then? They must have formed some kind of environment that was conducive to the next steps, an environment containing the potential for life itself – a ‘seed’ of life. From life on Earth, can we say anything about what seeds life? And if so, what might that say about the nature of aliens?

To my mind, the problem with most definitions of life is that they exclude the environment, the seed of life. Take the NASA working definition: ‘a self-sustaining system capable of undergoing Darwinian evolution’. Self-sustaining? At the very least, this does not emphasise the fact that life is always sustained by its environment. Not only did the first steps towards life depend on a facilitating environment, but even today we cannot cut our umbilical cord to the environment that sustains us. Like all living organisms, from bacteria to plants and animals, we need to respire continuously, just to go on living. The deep fear of drowning or asphyxiation is the fear of being separated from our environment for more than a few seconds. While a handful of living things have succeeded in separating the two for a while, in forming metabolically inactive spores that are capable of returning to life when conditions are suitable, they

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