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

Gwen Vasquez
July 14, 2017

The microscopic water-dwelling animal can live for 60 years and is about 0.5mm long.

Scientists have investigated what will kill the world's most indestructible species and concluded that nearly nothing can - except the death of the sun.

It can live for up to 30 years without food or water, endure temperatures as high as 150C, and even survive in the frozen vacuum of space.

Most previous studies of apocalyptic astronomical events - like asteroid impacts, neighboring stars going supernova or insanely energetic explosions called gamma-ray bursts - focused on their threat to humankind.

None of these events was thought to pose a lethal threat to the hardy tardigrade.

However, the hardy tardigrade could potentially survive even this.

"Although near supernovae or large asteroid impacts would be catastrophic for people, tardigrades could be unaffected", said co-author David Sloan.

So when that next mass extinction happens, it might be up to tardigrades to ensure life goes on.

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He observed: 'Tardigrades are as close to indestructible as it gets on Earth, but it is possible that there are other resilient species examples elsewhere in the universe.

"In this context there is a real case for looking for life on Mars and in other areas of the solar system in general", said Dr. Alves Batista said. "If tardigrades are Earth's most resilient species, who knows what else is out there?"

Objects such as dwarf planet Pluto are big enough to cause the oceans of the Earth to boil if they hit. So Loeb and colleagues calculated just how big an asteroid, how strong a supernova, or how powerful a gamma-ray burst would have to be to inject that much energy into Earth's oceans. Will there be any form of life left?

"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]."
The closest star to the Sun is four light years away and the probability of a massive star exploding close enough to Earth to kill all forms of life on it, within the Sun's lifetime, is negligible.

"(We) consider what cataclysmic event could lead to the annihilation of not just human life, but also extremophiles, through the boiling of all water in Earth's oceans", noted the study, which appeared in the journal Scientific Reports.

Establishing that the only possible way to eliminate all water bears would be to boil away all of the Earth's oceans, neither meteorites (too few), star supernovae or gamma-ray bursts (both too far away) would get the job done. If a tardigrade can survive these extreme conditions, then so may other creatures beyond the Earth's atmosphere. "Organisms with similar tolerances to radiation and temperature as tardigrades could survive long-term below the surface in these conditions". Not so for the tardigrade - a hardy, eight-legged creature that lives in in watery environments across Earth, from mountains to the deep sea.

Prof Abraham Loeb, co-author and chair of the Astronomy department at Harvard University, suggested Mars' history of once having a somewhat-habitable environment means we should be focusing there.

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