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Alien lifeforms might be living right under our noses, but how can we find them

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Science has operated on the assumption that life on earth arose only once, and all current lifeforms are evolved from a single common ancestor. Sarah Scoles writes in Aeon about a search for alien life here on earth.

In the late 1670s, the Dutch scientist Antonie van Leeuwenhoek looked through a microscope at a drop of water and found a whole world. It was tiny; it was squirmy; it was full of weird body types; and it lived, invisibly, all around us. Humans were supposed to be the centre and purpose of the world, and these microscale ‘animalcules’ seemed to have no effect – visible or otherwise – on our existence, so why were they here? Now, we know that those animalcules are microbes and they actually rule our world. They make us sick, keep us healthy, decompose our waste, feed the bottom of our food chain, and make our oxygen. Human ignorance of them had no bearing on their significance, just as gravity was important before an apple dropped on Isaac Newton’s head.

We could be poised on another such philosophical precipice, about to discover a second important world hiding amid our own: alien life on our own planet. Today, scientists seek extraterrestrial microbes in geysers of chilled water shooting from Enceladus and in the ocean sloshing beneath the ice crust of Europa. They search for clues that beings once skittered around the formerly wet rocks of Mars. Telescopes peer into the atmospheres of distant exoplanets, hunting for signs of life. But perhaps these efforts are too far afield. If multiple lines of life bubbled up on Earth and evolved separately from our ancient ancestors, we could discover alien biology without leaving this planet.

The modern-day descendants of these ‘aliens’ might still be here, squirming around with van Leeuwenhoek’s microbes. Scientists call these hypothetical hangers-on the ‘shadow biosphere’. If a shadow biosphere were ever found, it would provide evidence that life isn’t a once-in-a-universe statistical accident. If biology can happen twice on one planet, it must have happened countless times on countless other planets. But most of our scientific methods are ill-equipped to discover a shadow biosphere. And that’s a problem, says Carol Cleland, the originator of the term and its biggest proponent.

The idea came to Cleland, a philosopher at the University of Colorado at Boulder, when she spent a sabbatical year at the Centro de Astrobiología in Spain. She was studying the scientists, who were studying microorganisms.

‘If you have a sample of soil,’ she asked them, ‘how will you recognise what’s in it?’ The scientists rattled off the usual answers: slide it under a microscope, put it in a Petri dish, make millions of DNA copies, catalogue the genes. But that party line disturbed Cleland. ‘You couldn’t detect anything that wasn’t almost identical to familiar Earth life,’ she said. Their methods assumed that all microbes have genetic material that works like ours. Isn’t it possible, Cleland wondered, that life arose more than once here? If so, organisms from a second (or third) genesis would never turn up in our tests, because our tests are only meant to turn up familiar life. ‘But these organisms, if they exist, would leave traces in the environment,’ Cleland says.

In 2007 in the journal Studies in History and Philosophy of Biological and Biomedical Sciences, Cleland wrote about just such a trace: desert varnish. It’s a strange sheen, like a hardened waterfall, that covers desert rocks all over the planet. The streaks run down rocks from the desert of El Azizia in Libya to Antartica’s Dry Valley. Desert varnish – into which people have scraped petroglyphs for thousands of years – appears layer by layer, growing only the width of a human hair each millennium. The varnish is replete with arsenic, iron and manganese, although the rocks it coats are not. No known geochemical or biological process can account for its ingredients. And yet there it is. Since that discovery, Cleland has urged scientists not to discount – but to seek out – such anomalies as the varnish, things that don’t quite seem to fit. Because maybe they don’t fit.

Science’s modern-day explorers have unearthed increasingly anomalous organisms that are technically ‘familiar life’ – familiar in that they do adhere to the Central Dogma of molecular biology which explains the flow of genetic information in a biological system. Toxitolerants can live in nuclear waste; acidophiles can live in battery acid; obligate anaerobes die in the presence of oxygen; thermophiles thrive around hot vents deep in the ocean. Life, as they say in the movie Jurassic Park, finds a way.

But even the most familiar forms of life can be difficult to find. According to the latest estimates, we’ve discovered just 14 per cent of the dogma-following species on the planet. Of those, we can make only 1 per cent grow in the lab. A shadow biosphere might help us understand why. ‘Although we have good theoretical reasons for believing that life could be at least modestly different … we don’t know how different it could be,’ Cleland wrote in the seminal paper ‘The Possibility of Alternative Microbial Life on Earth’ (2005), co-authored with the astrobiologist Shelley Copley, also of the University of Colorado at Boulder. Just as a hammer and a sledgehammer can both pound a nail, other chemical combinations could lead to organisms that grow, adapt, respond to stimuli, and reproduce – that live, in other words. But which chemicals? And how? To understand that requires going back to the beginning. . .

Continue reading.

Written by Leisureguy

2 September 2017 at 11:21 am

Posted in Evolution, Science

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