The tiny tub­bies shall in­herit the Earth

The Guardian Weekly - - Discovery - Ni­cola Davis

Whether it is a su­per­nova or an as­ter­oid im­pact, should cos­mic calamity strike, it seems there will be at least one form of life left: a tubby, mi­cro­scopic an­i­mal that looks like a crum­pled vac­uum cleaner bag.

The crea­tures, known as tardi­grades, are stag­ger­ingly hardy an­i­mals, a mil­lime­tre or less in size, with species liv­ing in wet con­di­tions that range from moun­tain tops to chilly ocean wa­ters.

“They can sur­vive in­cred­i­ble con­di­tions – we are talk­ing close to ab­so­lute zero, the vac­uum of space, ex­po­sure to ra­di­a­tion that would kill us, and these things just walk away from it like noth­ing hap­pened,” said David Sloan, an as­tro­physi­cist from the Univer­sity of Ox­ford.

Now re­search by Sloan and col­leagues has shown that the crea­tures would sur­vive any cos­mic dis­as­ter that might con­ceiv­ably be thrown at Earth – a dis­cov­ery that could have im­pli­ca­tions else­where in the so­lar sys­tem, and be­yond.

“There are quite a lot of stars like our sun out there, and about 20% of these stars have an Earth­like planet around them,” said Sloan. “What you then want to ask is if life started on one of these plan­ets, what are the odds that it is still around?”

Writ­ing in the jour­nal Sci­en­tific Re­ports, the re­searchers de­scribe how they probed the co­nun­drum by ex­plor­ing the like­li­hood of a va­ri­ety of catas­tro­phes se­ri­ous enough to wipe out tardi­grades on an Earth-like planet, in­clud­ing a nearby su­per­nova, a burst of gamma rays, and an im­pact by a large as­ter­oid pow­er­ful enough to cause the oceans to boil. But the team found that the chances of such events were so re­mote as to be ex­tremely un­likely – there was lit­tle chance of a su­per­nova oc­cur­ring close enough to an Earth-like planet to kill off the crea­tures, and it would take an im­pact from an as­ter­oid or dwarf planet for the oceans to boil. “There are about 17 [as­ter­oids] this big in our so­lar sys­tem, but they are all on suf­fi­cient or­bits that they will never in­ter­sect with us,” said Sloan.

The up­shot, he said, was that it was very un­likely any cos­mic event would be so cat­a­strophic as to ster­ilise an Earth-like planet where life, of the sort we know, had got go­ing. “Be­cause [tardi­grades] are so hardy it means that events that we are wor­ried about as hu­man be­ings, and rightly so, cer­tainly

wouldn’t con­cern you if you just con­sid­ered all life,” said Sloan.

Matthew Cobb, pro­fes­sor of zo­ol­ogy at the Univer­sity of Manch­ester who was not in­volved in the study, said the find­ings were re­as­sur­ing for the fu­ture of life on Earth.

“It sug­gests that the com­plete erad­i­ca­tion of life on Earth is ex­tremely un­likely un­til we get to the point that the sun en­larges and all the oceans boil away,” he said.

But Cobb noted that even if the tardi­grades were the only sur­vivors, they would face a strug­gle: “For the tardi­grades to in­herit the Earth, what­ever catas­tro­phe swept over the planet would have to re­turn to nor­mal-ish con­di­tions within a mat­ter of decades at most, or it re­ally could be cur­tains.”

Mi­cro­scopic an­i­mals called tardi­grades would be able to with­stand al­most any cos­mic catas­tro­phe

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