Read part 2 of this article
While 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.
Advertisement
There鈥檚 hardly a niche on Earth that hasn鈥檛 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.
鈥淟ife on Earth has radiated into every conceivable 鈥� and in some cases almost inconceivable 鈥� ecological niche,鈥� says of the University of Arizona in Tucson, US.
The 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鈥檚 moon Europa, or in countless other spots beyond our solar system.
So here are some of Earth鈥檚 toughest organisms 鈥� although the record-setters are subject to debate.
Some like it hot
Steaming hot pools and scalding undersea hydrothermal vents provide a cosy habitat for heat-loving extremists.
Such 鈥榯hermophiles鈥� produce enzymes that are stable at high temperatures. Some have been isolated and put to work in everything from laundry detergents to food production.
The upper limit for life had been widely recognised as 113 掳Celsius, thanks to a microbe called Pyrolobus fumari that was in 1997 inside a single hydrothermal vent in the Atlantic Ocean, 3650 metres below the surface.
However, a microbe collected from a vent in what鈥檚 known as the Faulty Towers neighbourhood, 2400 metres down in the Pacific Ocean, has upped the ante.
It survived 鈥� and multiplied, scientists say 鈥� during a 10-hour blast in a 121 掳C autoclave, an oven used to sterilise medical equipment. Researchers finally managed to kill the hardy microbe by cranking the temperature up to 130 掳C. It鈥檚 been given the preliminary name of 鈥淪train 121鈥� and is in the same family as Pyrolobus fumari.
Hydrothermal vents may have existed once on Mars and may still exist in an ocean under Europa鈥檚 icy crust, some scientists say, making them prime targets in the search for extraterrestrial life.
Cold comfort
The most frigid polar regions and the darkest depths of the ocean are home for a few organisms that like a good chill.
Many are bacteria or similar single-celled organisms called Archaea, but some lichens called cryptoendoliths go to extremes by colonising pores in Antarctic rock. There鈥檚 also an alga that creates reddish 鈥榳atermelon snow鈥� 鈥� a phenomenon first described by Aristotle.
Cold-loving organisms, called psychrophiles, have specialised cell membranes that don鈥檛 stiffen in frigid temperatures, and many produce a kind of protein antifreeze.
It鈥檚 difficult to figure out the lowest temperature limit for life, says , a NASA scientist who studies life in cold, dry environments. That鈥檚 because as the mercury drops, growth slows 鈥� to the point where it鈥檚 almost imperceptible.
Microbes are known to grow at -12 掳C, and they survive at -20 掳C. Some studies even hint that a bacterium called Colwellia psychrerythraea strain 34H can withstand -196 掳C, the temperature of liquid nitrogen.
Research on cold-loving Earth organisms is especially valuable, McKay says, because 鈥渁ll the places in the solar system that may harbour life鈥� 鈥� like Mars and Europa 鈥� 鈥渁re cold and icy鈥�.
Salt of the Earth
Despite its name, the Dead Sea does harbour life. It鈥檚 the saltiest body of water on Earth, but a few microbes thrive there, in water eight times saltier than the ocean. 杏吧原创s studying one of them, Haloarcula marismortui, discovered that it has specialised proteins that protect it from the effects of salt.
杏吧原创s have theorised that any microbes living on Mars would have to be something like terrestrial halophiles in order to cope with the planet鈥檚 high salinity.
However 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.
Other scientists say it鈥檚 too soon to draw that conclusion, however, and McKay says there are probably regions on Mars that were not as harmful to life. 鈥淚t can鈥檛 be too salty everywhere,鈥� he told New 杏吧原创.
Click here to continue reading about extremophiles that can withstand high doses of radiation, acids and more.
