Published: Fri, July 14, 2017
Science | By Hubert Green

Earth's last survivors of an apocalyptic event will be water bears

Earth's last survivors of an apocalyptic event will be water bears

The British and U.S. scientists looked at the likelihood of tardigrades meeting a premature end as a result of extreme cosmic cataclysms such as exploding stars, giant asteroid impacts or gamma ray bursts - incredibly powerful eruptions of energy linked to the formation of black holes.

The famously hardy and arguably quite cute animal, which grows to a maximum length of half a millimetre, can live for up to 30 years without food or water, endure temperatures of up to 150 degrees and is so at home in the frozen vacuum of space that it has been known to mate.

The study, which was conducted by a team from Oxford University, examined a series of apocalyptic catastrophes and evaluated whether or not this creature could survive them.

In order to boil the oceans an exploding star would need to be 0.14 light-years away.

However, the hardy tardigrade could potentially survive even this.

Three possible cataclysmic events - an asteroid impact, a supernova and a gamma ray burst - were considered by the study.

"There are many more resilient species' on earth".

Physicist Dr David Sloan, co-author of the paper, said that he and his colleagues set out to see "just how fragile this hardiest life is".

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In highlighting the resilience of life in general, the research broadens the scope of life beyond Earth, within and outside of this solar system.

"To our surprise, we found that although nearby supernovas or large asteroid impacts would be catastrophic for people, tardigrades could be unaffected", he added. These explosions occur when enormous stars collapse or neutron stars collide; they're even rarer than supernovae, and astronomers have only seen them in distant galaxies.

None of the events - which would wipe out many species on Earth, humans included - would be powerful enough to "boil off" the planet's oceans. But the fact that tardigrades are so resistant to other potential apocalypses in the interim implies that "life is tough, once it gets going", Shostak says. There are many more resilient species' on earth.

While research has looked at the various ways human life will go extinct, very little academic work has looked at what it would take to extinguish all life on earth, according to the study.

Co-author Dr Rafael Alves Batista, also from Oxford University, said the ability of tardigrades to survive should spur on the search for life on Mars. Even subtle changes to our environment can have a drastic effect on our health.

"There is a third scenario, where life continues around geothermal vents on a rogue planet until capture by a new host system, or the source of heat is extinguished... life could [endure] on a rogue planet long enough for it to be recaptured [into another solar system]."
Professor Abraham Loeb, co-author and chair of the Astronomy department at Harvard University, said: 'It is hard to eliminate all forms of life from a habitable planet. "The history of Mars indicates that it once had an atmosphere that could have supported life, albeit under extreme conditions".

Subsurface oceans believed to exist on Jupiter's moon Europa and Saturn's Enceladus, "would have conditions similar to the deep oceans of Earth where tardigrades are found", said the authors.

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