Life under extreme conditions

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Syed Fattahul AlimbrHow sturdy is life The question naturally arises as the exobiologists are trying to know what kind of extremes life can stand as well as survive those. Answer to the question is important for knowing if life could evolve under the extreme conditions on the planets in the solar system or beyond that. How harsh is the condition elsewhere in the solar system or even outside it, say, on the planets of other stars or even in the interstellar spaces Such conditions may range from the extremely hot to the extremely cold to states where the pressure is very high to highly toxic and radioactive ones. The different planets and their moons in the solar system or in any of the planetary systems beyond the family of the sun in the stellar system may have such conditions on them. But man is still a long way from stepping outside for a longer interplanetary travel after moon landing some 39 years ago. The nearest planet, the conditions on which resemble earth in many respects, is the Mars. There is even a theory that life was brought to this earth on a rock that was catapulted from the red planet billions of years ago. This is another way of suggesting that life once existed on this now inhospitable planet. brBut when do the conditions become really intolerable for life Before man is finally prepared for the planetary voyage, he will have to get the answers to these basic questions. And to know the limits he may not have to travel really to other planets. These are certainly very extreme conditions that future space voyagers may come across in the distant parts of the solar system or even in the interstellar space. But life has been seen thriving in these harsh conditions, one cannot then just dismiss its possibility in other parts of the universe.brAnna Davidson of the New Scientist narrates below the forms of life that thrive under extreme conditions on this earth.brWhile scientists find ever more planets around other stars and contemplate missions to probe the far reaches of our own solar system, researchers are looking to the extremes of the Earth for clues about what kind of organisms could exist in the brutal conditions elsewhere.brThere's hardly a niche on Earth that hasn't been colonised. Life can be found in scalding, acidic hot pools, in the driest deserts, and in the dark, crushing depths of the ocean. It has even found a toehold in the frigid polar regions and in toxic dumps.brLife on Earth has radiated into every conceivable - and in some cases almost inconceivable - ecological niche, says Chris Impey of the University of Arizona in Tucson, US.brThe very existence of these hardy organisms hints that life might be able to eke out an existence in the cold, dry climate of Mars, the icy, acidic conditions of Jupiter's moon Europa, or in countless other spots beyond our solar system.brSo here are some of Earth's toughest organisms - although the record-setters are subject to debate.brSteaming hot pools and scalding undersea hydrothermal vents provide a cosy habitat for heat-loving extremists.brSuch 'thermophiles' produce enzymes that are stable at high temperatures. Some have been isolated and put to work in everything from laundry detergents to food production.brThe upper limit for life had been widely recognised as 113 °Celsius, thanks to a microbe called Pyrolobus fumari that was discovered in 1997 inside a single hydrothermal vent in the Atlantic Ocean, 3650 metres below the surface.brHowever, a microbe collected from a vent in what's known as the Faulty Towers neighbourhood, 2400 metres down in the Pacific Ocean, has upped the ante.brIt survived - and multiplied, scientists say - during a 10-hour blast in a 121 °C autoclave, an oven used to sterilise medical equipment. Researchers finally managed to kill the hardy microbe by cranking the temperature up to 130 °C. It's been given the preliminary name of Strain 121 and is in the same family as Pyrolobus fumari.brHydrothermal vents may have existed once on Mars and may still exist in an ocean under Europa's icy crust, some scientists say, making them prime targets in the search for extraterrestrial life.brThe most frigid polar regions and the darkest depths of the ocean are home for a few organisms that like a good chill.brMany are bacteria or similar single-celled organisms called Archaea, but some lichens called cryptoendoliths go to extremes by colonising pores in Antarctic rock. There's also an alga that creates reddish 'watermelon snow' - a phenomenon first described by Aristotle.brCold-loving organisms, called psychrophiles, have specialised cell membranes that don't stiffen in frigid temperatures, and many produce a kind of protein antifreeze.brIt's difficult to figure out the lowest temperature limit for life, says Chris McKay, a NASA scientist who studies life in cold, dry environments. That's because as the mercury drops, growth slows - to the point where it's almost imperceptible.brMicrobes are known to grow at -12 °C, and they survive at -20 °C. Some studies even hint that a bacterium called Colwellia psychrerythraea strain 34H can withstand -196 °C, the temperature of liquid nitrogen.brResearch on cold-loving Earth organisms is especially valuable, McKay says, because all the places in the solar system that may harbour life - like Mars and Europa - are cold and icy.brDespite its name, the Dead Sea does harbour life. It's the saltiest body of water on Earth, but a few microbes thrive there, in water eight times saltier than the ocean. Scientists studying one of them, Haloarcula marismortui, discovered that it has specialised proteins that protect it from the effects of salt.brScientists have theorised that any microbes living on Mars would have to be something like terrestrial halophiles in order to cope with the planet's high salinity.brHowever the results of recent explorations by the rover Opportunity, which found magnesium sulphate deposits that may have been left by salty water, have some scientists saying Mars may have been too salty to sustain any kind of life.brOther scientists say it's too soon to draw that conclusion, however, and McKay says there are probably regions on Mars that were not as harmful to life. It can't be too salty everywhere, he told New Scientist.brAcidic hot springs and geysers that would eat away at human flesh are no match for some organisms that also make themselves at home in the acid runoff from mines.brThe most extreme acidophiles known are microbes of the genus Picrophilus. They thrive at a pH of 0.7, and can grow down to a drain-clearing pH of 0. Both Mars, Europa and the clouds of Venus are thought to be acidic environments, so Earthly acidophiles intrigue scientists looking for life elsewhere.brEuropa's icy surface may be a potent mix of hydrogen peroxide and strong acids with a pH approaching 0, according to scientists who studied the spectral fingerprint of light reflected off the ice. If the acid on the surface is coming up from the ocean below, any life in the ocean would have to be tough.brThe most alkaline environments in the world are soda lakes, which can have a pH as high as 12, akin to ammonia. A number of microbes enjoy those caustic conditions, including Natronomonas pharaonis, which was first isolated from soda lakes in Egypt and Kenya in the 1980s.brAlkalis are substances that accept protons, while acids donate them. Because alkaline conditions damage cells, so-called alkaliphiles pump protons across their cell membranes to reduce the pH inside their cells.brThere are places on Mars, like Gusev Crater, which resemble soda lakes on Earth, according to an analysis of minerals by NASA's Spirit rover. The crater was formed by a meteorite impact billions of years ago, and if there were water on the planet back then, it would have accumulated in the crater, turning it into an evaporative lake.brRecently, living cells - many of which are Archaea from the Pyrococcus and Thermococcus genera - were found in a mud core taken from 1.6 km below the sea floor off the coast of Newfoundland. Though they represent the deepest life ever discovered beneath the sea floor, microbes of various kinds have been discovered at even greater depths under the continents. Communities of microorganisms have been found hunkered down in groundwater as far as 5 km below the surface of the land. Scientists think life exists even further down - to the point where the subsurface heat becomes unbearable for life.brEven the deepest part of the ocean, the Mariana Trench, which plunges 11 km below the surface of the Pacific Ocean near Guam, is inhabited. Globs of mud pulled from the trench have yielded an assortment of bacteria, fungi and primitive single-celled organisms called foraminifera. Video taken by an unmanned submersible that explored the area captured a sea cucumber, a scale worm and a shrimp in the trench, where the pressure would crush a human.brIn the most parched place on Earth, the Atacama Desert, which stretches nearly 1,000 km across South America, it rains only a few times a century. It's no coincidence that the desert has been used by filmmakers as a stand-in for Mars, and by NASA to test instruments bound for the cold, dry planet.brMicrobes like the bacterium Chroococcidiopsis have been found in the Atacama. But in its arid core, finally we think we've found an environment where it's too dry for life, McKay says.brWater is thought to be crucial for life because it provides a medium for nutrients to diffuse into cells and wastes to drift out, and a solvent for critical metabolic reactions.brEven though Mars appears to be dry as a bone, it may have boasted liquid water in the past. And some researchers say liquid water may periodically form just below the planet's surface - which may provide just enough of a toehold for life to survive there.