Life in the Extreme

Author: Jim Peaco, National Park Service. Source: nps.gov

Extromophiles

The conditions deemed necessary for life have been expanded & complicated in recent years, as we have found organisms living in extreme environments that we once thought were barren and even toxic. We are now looking for, and finding life in ever more ‘unlikely’ places. These extremophile organisms can thrive in a huge range of  different temperatures, pressures, acid or alkali. They can tolerate high concentrations of salt or sugar, high levels of radiation, survive in the absence of water and oxygen. Some live in 400 degree, sulphurous waters spewing from hydrothermal vents at the depths of the ocean or within rocks buried in our deepest mines & at the heart of glaciers. It is believed that all life needs certain basic elements such as hydrogen, oxygen, carbon, nitrogen, sulphur and phosphorus to function.  In 2010  a team of scientists led by Felisa Wolfe-Simon, a geo-microbiologist, claimed to have found aproteobacteria able use arsenic in place of phosphorus. This caused was much excitement and controversy  and the findings have since been refuted.

Life on Earth

So far there is only one place in the whole universe that we know supports life. Life here is all we know, all we have to go on. One of the most important implications for the extension of the conditions life needs to survive and thrive, is in our search for life beyond Earth. The more extreme environments we find supporting life, the wider we can cast our net to hunt down extraterrestrial lifeforms.

Some theories suggest that life may have arrived on Earth and even be exchanged between planets,  via meteorite impacts & ejections. Several species of bacteria have been found able to survive  and reproduce in hypergravity 400,000 times stronger than that of the Earth.  Deinococcus radiodurans is perhaps the toughest bacterium on or off the planet, able to withstand cold, dehydration, vacuum, acid and over 15,000 Gy (Gray unit of absorbed radiation) of ionized radiation. For comparison a dose of 5 Gy can kill a human.

To test the theory that life can survive for extended periods in interplanetary space, the Planetary Society devised the LIFE Experiment to send organisms representing each of the three domains of life: eukaryotea, bacteria and archaea into space. The plan was to send ten organisms on the 34 month round trip to Mars aboard the Russian Phobos-Grunt probe. Unfortunately the probe never left  orbit and crashed back to Earth on January 15, 2012, The whereabouts of the fragments that survived re-entry, possibly including the LIFE capsule is unknown. One of the organisms included in the ill fated mission were Tardigrades , a hardy microscopic animal, found all over our planet from the Himalayas to the deepest ocean and from the equator to the poles.

Life Beyond Earth

The range of conditions that we call extreme, may be normal conditions elsewhere in the universe. So while we hunt for ‘Earth’s Twin’ orbiting in the habitable zone surrounding a Sun-like star, the definition of the conditions needed to support life is being extended all the time as we find organisms in ever more bizarre locations at home. Though life on Earth is dependent on carbon and water, given enough time, evolution may be able to adapt life beyond even those limits. For now we can only confine our search to those places that we think offer the best chance of finding life.  There are current, or planned missions, searching in what we think may be likely places within our Solar Sytem: on Mars, Europa, Callisto, Enceladus, but what about the unlikely places? Is Earth special? You bet it is, but life may be more resilient than we know.

About Jenny Winder

ScienceWriter at Urban Times/URBNFUTR. Broadcaster on Under British Skies at Astronomy FM Radio. On Twitter as @astrojenny StarWatcher MusicLover Harpist Singer BookWorm BSLUser OUJunky WooBasher...

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