In the end, there will be tardigrades.

If a cataclysm wipes out most of life on the planet — including humans — it’s likely that tardigrades will survive. These oddly cute microscopic animals are among the toughest creatures on Earth.

Some can withstand the shock of boiling water and temperatures that near absolute zero. Others have survived in the crushing pressures of the deep ocean or go without water for decades. Tardigrades have survived in the vacuum of space. In 2014, Japanese researchers thawed a group of tardigrades that had been frozen for 30 years. What did they do after they woke up? They reproduced.

But what would it take to ... kill them all? (Laughs maniacally.)

What would it take to end all life on Earth?

That’s roughly the question a group of physicists asked in a new paper in Nature’s Scientific Reports journal.

The point of the paper isn’t to pick on tardigrades. Rather, it’s a thought experiment.

“Much attention has been given in the literature to the effects of astrophysical events on human and land-based life,” the authors, physicists from Oxford and Harvard, write. “However, little has been discussed on the resilience of life itself.”

This question is important because if a mass extinction event were to occur, it would be nice to know if life could again grow, evolve, and prosper. The asteroid impact that killed the dinosaurs 66 million years ago also took out 80 percent of the other species on the planet. But some small mammals survived. And that’s why we’re here today.

Tardigrades are good benchmark on this question. If the extremely tough tardigrades go, then, the Earth, in the word of the researchers, would be “sterilized” of all life.

Why tardigrades are so damn tough

It’s important to note: Tardigrades are basically indestructible only when they enter a special state called cryptobiosis.

In harsh environments, the animals tuck in their legs and expel all moisture from their bodies. In this state, they're called tuns.

As tuns, the tardigrades produce glycerol (antifreeze), and secrete trehalose, a simple sugar with remarkable preservation properties. "Trehalose is viewed as a cocoon that traps the biomolecule inside a glassy matrix, like amber-encasing insects," explains a 2009 paper in Protein Science. When the trehalose crystallizes, the tardigrade becomes mummified in a glass suit of armor. As a tun, the tardigrade reduces its metabolism by 99.99 percent as it waits for a more suitable environment.

Different species of tardigrades have different adaptations for a wide variety of environmental threats. In hot conditions, they release heat-shock proteins, which prevent other proteins from warping. Some tardigrades can form bubbly cysts around their bodies. Like puffer jackets, the cysts allow them to survive in harsh climates.

(When tardigrades are not in tun form, "it's very easy to kill them," a biologist once assured me.)

Three scenarios that could wipe out tardigrades

So what would it take? The researchers made some assumptions about tardigrades’ upper limit for heat and radiation exposure, and examined three scenarios.

A nearby star goes supernova and sends deadly radiation pummeling toward Earth A gamma ray burst from an unknown origin fries Earth Asteroid impact

Let’s start from the top.

In the case of 1 and 2, hell would be unleashed on Earth. The radiation would destroy the ozone layer, fry all life on land, and destroying our oxygen-rich atmosphere. However, in these scenarios, the tardigrades could still survive. “Even the complete loss of the atmosphere would not have an effect on species living at the ocean’s floor,” the study authors note.

To really kill all the tardigrades — and all life on the planet — you’d need to vaporize the oceans. Which would take an incredible amount of energy.

How much?

560,000,000,000,000,000,000,000,000 joules of energy, the study’s authors compute. A joule is a measure of energy equal to the effort it takes to create one watt of power for one second. 560 septillion of them is “around a million years of total human energy production at current rates,” the authors note in the Conversation.

Luckily, there’s no star within striking distance that could produce such energy.

Gamma ray bursts are a lot more mysterious.

We’ve only seen them in other galaxies, and they’re some of the most energetic events ever observed in the universe. Scientists are not sure how or why they form. But they could absolutely destroy all life on the Earth.

Luckily, this scenario is unlikely. The source of a gamma ray burst would have to be “within about 42 light-years,” the authors write. The chances of that are astronomically small. Again, we’ve never seen a gamma ray burst in our own galaxy. So it’s unlikely one will pop up in our neighborhood.

Actually, few planets in the galaxy “would ever be sterilized by a gamma-ray burst.”

Phew!

That leaves asteroids. Could a big enough asteroid produce the energy needed to end all life on the planet?

Yes!

The physicists estimate it would take an asteroid with a mass of 1.7 quintillion kilograms or greater to incinerate the oceans. There are only 19 of these in the solar system. None are on a collision course with Earth. The authors also suggest that if the dwarf planet Pluto slammed into the Earth, it would do the trick. And then finally we’d be rid of the little stubby-legged buggers (and absolutely everything else.)

A few caveats

As the Washington Post points out, there are some important caveats to this paper.

The big one is researchers are lumping all tardigrades together in their analysis. There are thousands of species of tardigrade — and they all have slightly different adaptations that help them survive. But no one species contains all the defenses of the others.

The ones that live in the deep, deep ocean may not be able to withstand as much heat, radiation, or other traumas as their counterparts on land. So it’s a bit of a rough sketch. Tardigrades might be a bit easier to kill than what’s implied here.

But for all the talk of death and destruction, the study authors have an optimistic conclusion: "We do not fully understand the mechanisms by which life started, but once it exists on an Earth-like planet, the complete removal of all life (other than through evolution of the host star) is a very unlikely event.”</s>The new study published in Scientific Reports, has shown that the tiny creatures, will survive the risk of extinction from all astrophysical catastrophes, and be around for at least 10 billion years - far longer than the human race.

Although much attention has been given to the cataclysmic impact that an astrophysical event would have on human life, very little has been published around what it would take to kill the tardigrade, and wipe out life on this planet.

The research implies that life on Earth in general, will extend as long as the Sun keeps shining. It also reveals that once life emerges, it is surprisingly resilient and difficult to destroy, opening the possibility of life on other planets.

Tardigrades are the toughest, most resilient form of life on earth, able to survive for up to 30 years without food or water, and endure temperature extremes of up to 150 degrees Celsius, the deep sea and even the frozen vacuum of space. The water-dwelling micro animal can live for up to 60 years, and grow to a maximum size of 0.5mm, best seen under a microscope. Researchers from the Universities of Oxford and Harvard, have found that these life forms will likely survive all astrophysical calamities, such as an asteroid, since they will never be strong enough to boil off the world's oceans.

Three potential events were considered as part of their research, including; large asteroid impact, and exploding stars in the form of supernovae or gamma ray bursts.

There are only a dozen known asteroids and dwarf planets with enough mass to boil the oceans (2x1018 kg), these include (Vesta 2x1020 kg) and Pluto (1022 kg), however none of these objects will intersect the Earth's orbit and pose a threat to tardigrades.

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

Gamma-ray bursts are brighter and rarer than supernovae. Much like supernovas, gamma-ray bursts are too far away from earth to be considered a viable threat. To be able to boil the world's oceans the burst would need to be no more than 40 light-years away, and the likelihood of a burst occurring so close is again, minor.

Dr Rafael Alves Batista, Co-author and Post-Doctoral Research Associate in the Department of Physics at Oxford University, said: "Without our technology protecting us, humans are a very sensitive species. Subtle changes in our environment impact us dramatically. There are many more resilient species' on earth. Life on this planet can continue long after humans are gone.

"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. If Tardigrades are earth's most resilient species, who knows what else is out there."

Dr David Sloan, Co-author and Post-Doctoral Research Associate in the Department of Physics at Oxford University, said: "A lot of previous work has focused on 'doomsday' scenarios on Earth - astrophysical events like supernovae that could wipe out the human race. Our study instead considered the hardiest species - the tardigrade. As we are now entering a stage of astronomy where we have seen exoplanets and are hoping to soon perform spectroscopy, looking for signatures of life, we should try to see just how fragile this hardiest life is. To our surprise we found that although nearby supernovae or large asteroid impacts would be catastrophic for people, tardigrades could be unaffected. Therefore it seems that life, once it gets going, is hard to wipe out entirely. Huge numbers of species, or even entire genera may become extinct, but life as a whole will go on."

In highlighting the resilience of life in general, the research broadens the scope of life beyond Earth, within and outside of this solar system. Professor Abraham Loeb, co-author and chair of the Astronomy department at Harvard University, said: "It is difficult 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. Organisms with similar tolerances to radiation and temperature as tardigrades could survive long-term below the surface in these conditions. The subsurface oceans that are believed to exist on Europa and Enceladus, would have conditions similar to the deep oceans of Earth where tardigrades are found, volcanic vents providing heat in an environment devoid of light. The discovery of extremophiles in such locations would be a significant step forward in bracketing the range of conditions for life to exist on planets around other stars."

Explore further: More to life than the habitable zone

More information: 'The Resilience of Life to Astrophysical Events' David Sloan, Rafael Alves Batista, and Abraham Loeb, Scientific Reports (2017). www.nature.com/articles/s41598-017-05796-x</s>The world’s most indestructible species, say scientists, is the tardigrade, an eight-legged micro-animal, also known as the water bear. The tiny creature will survive the risk of extinction from all astrophysical catastrophes, and be around for at least 10 billion years – far longer than the human race. That’s according to a study published today (July 14, 2017) in the journal Scientific Reports.

The research implies that life on Earth in general, will extend as long as the sun keeps shining. It also suggests that once life emerges, it is surprisingly resilient and difficult to destroy, opening the possibility of life on other planets.

Tardigrades are have a reputation as the toughest, most resilient form of life on earth. They can live for up to 60 years, are able to survive for up to 30 years without food or water, and endure temperature extremes of up to 150 degrees Celsius (300 degrees F), the deep sea and even the frozen vacuum of space. The tiny, water-dwelling animal – maximum size is 0.5mm (.2 inches) – is best seen under a microscope. The researchers – from the Universities of Oxford and Harvard – say that tardigrades will likely survive all astrophysical calamities, including an asteroid, since they will never be strong enough to boil off the world’s oceans.

Rafael Alves Batista of the Department of Physics at Oxford University, is a study co-author. Batista said in a statement:

Without our technology protecting us, humans are a very sensitive species. Subtle changes in our environment impact us dramatically. There are many more resilient species’ on earth. Life on this planet can continue long after humans are gone. 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. If tardigrades are earth’s most resilient species, who knows what else is out there.

According to an Oxford statement, three potential events were considered as part of their research, including; large asteroid impact, and exploding stars in the form of supernovae or gamma ray bursts.

Asteroids: There are only a dozen known asteroids and dwarf planets with enough mass to boil the oceans (2×10^18 kg), these include (Vesta 2×10^20 kg) and Pluto (10^22 kg), however none of these objects will intersect the Earth’s orbit and pose a threat to tardigrades. Supernova: In order to boil the oceans an exploding star would need to be 0.14 light-years away. 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. Gamma-Ray bursts: Gamma-ray bursts are brighter and rarer than supernovae. Much like supernovas, gamma-ray bursts are too far away from earth to be considered a viable threat. To be able to boil the world’s oceans the burst would need to be no more than 40 light-years away, and the likelihood of a burst occurring so close is again, minor.

It is difficult, the researchers say, to eliminate all forms of life from a habitable planet. In highlighting the resilience of life in general, the research broadens the scope of life beyond Earth, within and outside of this solar system.

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Bottom line: Tiny, eight-legged marine creatures called tardigrades are likely to survive on Earth until the sun dies, long after humans have disappeared, says a new study.

Read more from University of Oxford</s>Tardigrades will be the last surviving species on Earth and could live through any doomsday event, scientists have claimed.

Also known as water bears, tardigrades can survive for up to 30 years without food or water and are the toughest creatures on Earth.

Now a new study by Oxford University has found the hardy micro-animals will exist for at least 10 billion years and could live through an asteroid strike or the impact of a close-by exploding star.

The research was designed to determine the extreme conditions under which life might die on Earth - and it could have implications for finding life elsewhere in the solar system.

WHAT DOOMSDAY EVENTS COULD THE TARDIGRADE LIVE THROUGH? Three potential events were considered as part of their research, including asteroid strikes, exploding stars in the form of supernovae and gamma-ray bursts. Because of the tardigrade's unique characteristics, they could only die off if all the world's oceans were boiled during a doomsday event, the researchers said. They reasoned that there are only a dozen known asteroids and dwarf planets with enough mass to boil the oceans, these include Vesta and Pluto. However none of these objects will intersect the Earth's orbit and pose a threat to tardigrades, the researchers found. In order for an exploding star to to boil the oceans, it would need to be around 0.14 light-years away from Earth, the researchers found. But 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 is negligible, they found. Gamma-ray bursts are brighter and rarer than supernovae. Much like supernovas, gamma-ray bursts are too far away from earth to be considered a viable threat.

The eight-legged animals, which grow to about half a centimetre long (0.02 inches), can also withstand temperature extremes of up to 150°C (302°F).

They are also resistant to radiation levels of 5000 to 6200 Gy, which is around the dose used in some forms of chemotherapy.

Researchers from Oxford University have studied the animal's risk of extinction for a range of astrophysical disasters.

Dr Rafael Alves Batista, a researcher at the department of physics at Oxford University, told MailOnline: 'The goal is to study what is necessary to kill all life, not just humans.

'To this end, we have chosen the most resilient form of life we know: tardigrades.

'The question we want to answer is: what would it take to kill all life on a planet? In order to achieve that, we need something that can kill tardigrades.'

The research found that the tiny creatures could survive an asteroid strike, supernova or a gamma-ray burst, a kind of extreme energetic explosion.

Though all these events would be deadly to humans, none could see off the tardigrades, the researchers found.

Dr Alves Batista said: 'Without our technology protecting us, humans are a very sensitive species.

'Subtle changes in our environment impact us dramatically. There are many more resilient species' on earth.

'Life on this planet can continue long after humans are gone.'

They concluded that the animals will live on Earth for at least ten billion years, and will only be wiped out when the sun burns out.

Dr David Sloan, a researcher from the department of physics at Oxford University, said: 'A lot of previous work has focused on 'doomsday' scenarios on Earth - astrophysical events like supernovae that could wipe out the human race.

'Our study instead considered the hardiest species - the tardigrade.

'As we are now entering a stage of astronomy where we have seen exoplanets and are hoping to soon perform spectroscopy, looking for signatures of life, we should try to see just how fragile this hardiest life is.

To our surprise we found that although nearby supernovae or large asteroid impacts would be catastrophic for people, tardigrades could be unaffected.'

Three potential events were considered as part of their research, including asteroid strikes, exploding stars in the form of supernovae and gamma-ray bursts.

Researchers chose to focus on these events as they are the only known astrophysical phenomena that could end life on Earth.

Because of the tardigrade's unique biological characteristics, they could only die off if all the world's oceans were boiled during a doomsday event, the researchers said.

They reasoned that there are only a dozen known asteroids and dwarf planets with enough mass to boil the oceans, these include Vesta and Pluto.

However none of these objects will intersect the Earth's orbit and pose a threat to tardigrades, the researchers found.

And in order for an exploding star to to boil the oceans, it would need to be around 0.14 light-years away from Earth, the researchers found.

But 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 is negligible, they found.

Gamma-ray bursts are brighter and rarer than supernovae.

Much like supernovae, gamma-ray bursts are too far away from earth to be considered a viable threat.

To be able to boil the world's oceans the burst would need to be no more than 40 light-years away, and the likelihood of a burst occurring so close is minor.

The findings indicates that, despite species loss, life itself can survive almost any form of adversity.

'It seems that life, once it gets going, is hard to wipe out entirely,' Dr Sloan said.

'Huge numbers of species, or even entire genera may become extinct, but life as a whole will go on.'

The results suggest that life itself is resilient enough to persist in the most inhospitable corners of the universe, according to the researchers.

'Planets (and satellites) that could once have hosted life and seem inhospitable today could still harbour some resilient die-hard creatures,' said Dr Alves Batista.

'Mars, for instance, lost its atmosphere, but could have hosted life in the past.

'Our work suggests that the search for life in such places is justified even if the planet doesn't seem hospitable.'

The researchers added that other lifeforms possessing the remarkable qualities of the tardigrade may exist in other parts of the universe.

'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', said Dr Alves Batista.

'If Tardigrades are Earth's most resilient species, who knows what else is out there.

'There might exist other creatures similar to tardigrade in other places. We have to keep searching.'

The research was published in Scientific Reports.</s>The odds of finding life on another planet hinge on the answers to two big questions. First, how often does life arise? Second, once it does arise, how likely is it to persist without being completely wiped out? The first question is extremely difficult, especially since we have exactly one example of a life-spawning planet. But the second question is easier to answer—at least for Earth—and a trio of astrophysicists have given it a shot. In a paper delightfully titled “The Resilience of Life to Astrophysical Events,” David Sloan and Rafael Alves Batista, both from the University of Oxford, and Avi Loeb, from Harvard University, estimated the odds that a space-borne catastrophe like an incoming asteroid would completely sterilize the Earth. Reassuringly, they think those odds are astronomically low—about one in 10 million for every billion years. “The conclusion we come to is that life, once it starts anywhere, is hard to eradicate,” Sloan says. In other words: Life finds a way (even if you bludgeon it with a giant space rock or an exploding star).

To be clear, the three researchers aren’t concerned with the fate of humans—a fragile, fleshy species that, in Loeb’s words, can be “killed by climate change or affected by bad politics.” Instead, the trio wanted to know what it would take to wipe out all life on the planet. And to do that, they focused on the world’s hardiest animals—the tardigrades. Tardigrades, also known as water bears, are microscopic, eight-legged, water-living animals. They’re oddly endearing with their shuffling gaits, rotund bodies, and puckered mouths. They’re also the epitome of resilience. In stressful environments, they can expel all the water in their bodies and enter a shriveled, dormant state. In this form, as I’ve written before, they don’t need food or water. They can endure temperatures close to absolute zero for a few minutes, and as high as 151 degrees Celsius for a few decades. They can withstand the intense pressures of the deepest ocean, doses of radiation that would kill other animals, and baths of toxic solvents. They are, to date, the only animals that have been exposed to the naked vacuum of space and lived. If you want to know what it would take to sterilize the world, you need to know what it would take to kill tardigrades.

Sloan, Batista, and Loeb consider three possible killers: a colliding asteroid, like the one that killed most of the dinosaurs; a nearby star going supernova; and gamma-ray bursts—high-energy explosions unleashed by some distant stellar calamity. “Within the lifetime of the sun, tardigrades will likely survive.” In the case of the asteroid, anything that was directly punched by the rock would obviously be in bad shape, but the collision would also throw up so much dust that it could block out the sun and instigate a global freeze. The supernova and the gamma-ray bursts would both kill in similar ways. They’d pummel the planet with intense radiation. They’d destroy the ozone layer, allowing yet more radiation to reach the surface. They’d convert nitrogen and oxygen in the atmosphere into nitrous oxide, which would create acid rain and a sun-blocking smog. All of these scenarios would be very bad news for humans and for anything else on land. But species that live underground or in the deep oceans—including many tardigrades—would be largely shielded by soil or water. They already survive in the absence of sunlight. You couldn’t acidify the oceans enough to kill them. You could irradiate them, but these animals are exceptionally resistant to radiation, which would also get weakened by any overlying water. Sloan, Batista, and Loeb calculated that the amount of radiation it would take to kill a tardigrade on the ocean floor would also cause the oceans to boil—a far more pressing issue. The extended heat would kill them before the radiation did.

So sterilizing the world, er, boils down to heat. Could an astronomical cataclysm impart enough energy onto our blue marble to raise the temperature of its water beyond 100 degrees Celsius? An asteroid could do it if it weighed more than 1.7 quadrillion metric tons, making it somewhere between 10 and 1,000 times heavier than the rock that smote the dinosaurs. In our solar system, there are only 19 known asteroids that are big enough (along with a few dwarf planets like Pluto), and none of their orbits coincide with Earth’s. Beyond our solar system, the three researchers calculate that the odds of being struck with one of these life-ending monsters within a billion-year timespan is just one in 100,000. Supernovas and gamma-ray bursts both release ocean-boiling amounts of energy, but that energy dissipates with distance. To annihilate all tardigrades, a supernova would need to happen at most 0.13 light-years away. Our closest star, Proxima Centauri, is already 4.25 light-years away and is too small to go supernova; even if it did, it would raise the ocean’s temperatures by a paltry 0.1 degrees Celsius. “If life did get started elsewhere in the galaxy, we should expect it to still be there.” All of these calculations are based on the Earth, but we’re not alone in our safe distance. Batista created a simulation that accounts for the density of stars throughout our galaxy, and the fact that those in the center are more closely packed. But even there, only 1 percent of planets would eventually be sterilized by an exploding star. Gamma-ray bursts are also unlikely annihilators. Based on how often they happen, the odds that they would occur within the sterilization radius of a planet are just one in 10 billion for every billion years. (Again, we’re talking about what it would take to kill tardigrades. “The death sphere gets much bigger when you consider an animal like us,” says Sloan. “God, I just invented the phrase ‘death sphere’. That’s scary.”)

Eventually, the sun will expand and potentially engulf the Earth in fire, before collapsing and triggering a permanent freeze. “The end of the sun would terminate life on Earth, but before then, it’s unlikely that astrophysical phenomena would do it,” says Loeb. “Within the lifetime of the sun, tardigrades will likely survive.” And tardigrades are only the hardiest animals around. If they can survive, microbes probably will, too. The Earth has experienced at least five major mass extinctions in its history, where the majority of living species disappeared forever, but something always survived these brushes with oblivion. And even in the face of far greater calamities, Sloan, Batista, and Loeb think that life would still persist in some form. Clark Chapman, from the Southwest Research Institute, endorses their conclusion. “While human civilization, as it exists today, is at some very small risk,” he says, “it is virtually certain that Earth cannot be sterilized for billions of years.” Still, he notes that things may have been different in the solar system’s past, “when bodies vastly larger than today’s asteroids and comets collided with planets that might have already had life and sterilized them.” The Earth, for example, was possibly hit by a Mars-sized object in its early history, creating the Moon. Besides, Chapman says, nobody knows if evolution on other planets would tick along in the same way as it has on Earth. Would it spawn tardigrade-like organisms that tolerate extreme conditions? Would those organisms find shelter in safe spaces like deep oceans? “It’s highly speculative to guess about the evolution and survivability of life on extra-solar worlds," he says. Sloan admits that he and his colleagues made a lot of assumptions in their work. But when scientists think about life beyond our planet, they cannot help but use life on our planet as a starting point. And Sloan now feels more optimistic about the search for such life. In the last few decades, astronomers have discovered thousands of other planets that lie beyond our solar system. Some of these exoplanets are Earth-sized, and some orbit the habitable zones of their respective stars—the Goldilocks region where they get enough heat, but not too much. Whether they—or closer neighbors like Mars—are home to life is an open question. But “if life did get started elsewhere in the galaxy,” says Sloan, “we should expect it to still be there.”</s>Scientists have found Earth’s most resilient species, and it’s not the cockroach.

A new study, published in the journal Scientific Reports, determined that the tardigrade, an eight-legged micro-animal, will outlive us all.

“Tardigrades are as close to indestructible as it gets on Earth,” study co-author Rafael Batista, from Oxford University, said in a statement.

The hardy microscopic animals, also known as water bears, are able to survive for up to 30 years without food or water. According to the paper, they can endure temperature extremes as low as -272 degrees Celsius and as high as 150 degrees Celsius. They can even survive the deep sea, the frozen vacuum of space and radiation levels comparable to more than 70 times the amount of radiation given to treat cancer.

In comparison, humans could be wiped out pretty easily.

“Without our technology protecting us, humans are a very sensitive species,” Batista said.

“Subtle changes in our environment impact us dramatically. There are many more resilient species on Earth. Life on this planet can continue long after humans are gone.”

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.

The study’s researchers from Oxford and Harvard University came to the conclusion that the only thing to wipe out life on earth would be if the oceans boiled.

And according to them, there are three types of cataclysmic events that could make that happen: a large asteroid impact, a supernova and a gamma-ray burst.

But after careful analysis, the researchers concluded that all of these events were quite unlikely.

In the paper, they write that there are only a dozen known asteroids and dwarf planets with enough mass to boil the oceans, including Pluto. However, none of those objects cross the Earth’s orbit.

For a supernova to cause our oceans to boil the exploding star would need to be 0.14 light-years away, and our closest star, the sun, is four light years away.

Finally, gamma-ray bursts are also too far away from earth to be an actual threat.

After ruling out the multiple end-of-the-world scenarios, the study concluded that the microscopic creatures will be around for at least 10 billion years and could survive all astrophysical catastrophes, since none would be strong enough to boil off the world’s oceans.

David Sloan, another co-author on the paper from Oxford University found this to be quite comforting.

“Huge numbers of species, or even entire genera may become extinct, but life as a whole will go on,” he said.

The researchers say this discovery also broadens the scope for extraterrestrial life.

“There is a real case for looking for life on Mars and in other areas of the solar system in general. If Tardigrades are earth's most resilient species, who knows what else is out there,” said Batista.</s>The freak shall inherit the Earth

Tardigrades, as the water bears are more prosaically known, have long fascinated scientists with their veritable superpowers of survival. — Handout via AFPPARIS, July 14 — If a monster space rock crashes into our planet or radiation from an exploding star boils our oceans, humans and most other life forms will disappear.

But one creature is sure to survive, according to a study published today.

And it will keep going for as long as the Sun doesn’t die — at least another 10 billion years.

Earth’s designated heir is the tardigrade, a microscopic, grub-like, eight-legged animal that can live in water or on land, in extreme pressure high or low.

Also known as a water bear or moss piglet, it can withstand sizzling heat, freezing cold, and high radiation, 30 years without food, and even being dried to a crisp.

Despite its diminutive size — under a millimetre (0.04 inches) — it is considered the world’s toughest animal.

The tardigrade, said researchers from Oxford and Harvard, will survive all foreseeable astrophysical catastrophes — asteroid strikes, exploding stars (supernovae) or gamma ray bursts — and “be around for at least 10 billion years.”

That is far better than the diagnosis for our own species.

“Without our technology protecting us, humans are a very sensitive species. Subtle changes in our environment impact us dramatically,” said Rafael Alves Batista of Oxford University, a co-author of the study in the journal Scientific Reports.

“There are many more resilient species on Earth. Life on this planet can continue long after humans are gone.”

Batista and a team set out to determine what kind of a catastrophe would be required to wipe Earth clear of all life.

And they found it would be nigh impossible — once life takes root, it is surprisingly difficult to eradicate.

Supernovae or gamma-ray bursts, electromagnetic explosions that happen in other galaxies, could deplete the Earth’s protective ozone layer which protects us from radiation. But life could continue below ground, and deep under water.

Even a complete loss of atmosphere would not affect species on the ocean floor.

A large asteroid strike could cover the Earth in a cloud of Sunlight-blocking dust, causing temperatures to drop and a so-called “impact winter.”

Creatures dependent on light would die off, but in volcanic vents in the deep ocean, life would continue.

No space rock big enough to cause a complete species annihilation is on a collision course with our planet, the team found.

Nor are there massive stars or potential gamma ray sources near enough to boil Earth’s oceans if they erupted.

The only event that would kill even the tardigrades, is when the Sun eventually burns out.

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

Tardigrades have a body divided into four segments, each with a pair of legs ending in sharp claws.

They live in moss, on plants, in sand, in fresh water or in the sea.

Water bears can survive temperatures as high as 150°C and as low as minus 270°C.

They can come back from being dried out to a lifeless husk for decades, and withstand near-zero pressure in outer space as well as the crushing depths of the Mariana Trench, 11 kilometres (below sea level.

They can survive radiation up to 6,200 gray (Gy). A dose of 6 Gy can kill a human.

The tardigrade’s extreme resilience points to another tantalising possibility — the existence of life elsewhere in our Solar System in places once thought too hostile.

If a tardigrade can survive these extreme conditions, then so may other creatures beyond Earth’s atmosphere.

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. — AFP</s>Microscopic tardigrades, also known as “water bears,” are the toughest animals on the planet, capable of withstanding intense radiation, extreme temperatures, and even the vacuum of space. In a fascinating new study, researchers have shown that tardigrades are poised to survive literally anything that nature throws at them—and that of the animals alive today, they’ll be the last ones standing before the Sun annihilates the Earth billions of years from now.

The point of this cheery study, published today in Scientific Reports, was to determine the conditions under which all life on Earth might be extinguished, and the phenomena that could instigate the premature sterilisation of the planet. The word premature is key; the Sun could sterilise the Earth in as few as two billion years, and engulf it in about five to seven billion years when it turns into a red giant. But that’s not what this research team was interested in. They wanted to know if something else might be capable of exterminating all life on our planet.

Such an exercise is not completely frivolous. The answer to this question could tell us about the resiliency of life, and the extreme conditions under which it can survive—or not survive—on Earth, Mars, the frigid subterranean waters of Europa, or some dark corner of the Milky Way. As Avi Loeb, an astronomer at the Harvard-Smithsonian Center for Astrophysics and a co-author of the new study, told Gizmodo, “I was curious about which astrophysical phenomena can eradicate life, so this can guide us in which environments we should not search for life.”

First, Loeb and his colleagues had to answer one fundamental question: which animal on Earth is the toughest to kill? That animal, to virtually no one’s surprise, is the freakishly durable tardigrade. This eight-legged wee beastie (they measure 0.5 mm in length and can only be seen through a microscope) can endure conditions that boggle the imagination, surviving for up to 30 years without food or water, and enduring temperature extremes of up to 300 degrees F (150 degrees C). Tardigrades can withstand blasts of radiation, complete dehydration, being frozen, the vacuum of space, and even the intense pressure found at the bottom of the Marianas Trench.

It should come as little surprise, therefore, that these animals, which emerged 350 million years ago during the Cambrian Era, have managed to survive no less than five mass extinctions.

With the tardigrade chosen, Loeb’s team then explored the various ways in which this creature could be completely wiped off the planet. Incredibly, they found that these ancient extremophiles will likely survive all natural calamities—from asteroids and supernovae through to gamma-ray bursts and wandering stars—because none of these events are likely to trigger the only thing that can truly destroy all tardigrades: the boiling off of the world’s oceans.

Yes, you read that right—it’ll only be when the oceans boil away and the planet is a dry as a bone that the tardigrade family will meet its demise.

Loeb and his colleagues, Rafael Batista and David Sloan, both from Oxford University, say tardigrades would be able to survive the destruction of the Earth’s atmosphere or a runaway greenhouse effect by seeking shelter in the ocean, which is why they were forced to consider astrophysical events powerful enough to deplete the planet of water. To that end, the researchers considered the potential for asteroid strikes, supernovae, and gamma-ray bursts to do the job. Yet none of these celestial phenomena seemed powerful enough.

Tardigrades would be able to survive a massive asteroid strike, according to the new research (Image: ESA)

There are only about a dozen known asteroids and dwarf planets big enough to pack such a punch that the ensuing heat would boil away the oceans. These include Vesta and Pluto, but as the researchers point out, none of these objects are poised to intersect Earth’s orbit.

In terms of a supernova, where a star blows itself to smithereens, an exploding star would have to be 0.14 light years away, or 8,900 AU (where 1 AU equals average distance of the Earth to the Sun) to do the trick. The closest star to Earth is four light-years away, so the probability of a massive star extinguishing all life on Earth is practically negligible. Interestingly, a passing star came within 0.8 light-years of our Sun around 70,000 years ago. But such events are exceptionally rare, and the odds of a star going supernova at precisely the exact moment when it’s closest to Earth is astronomically high.

Relatedly, a wandering star could pass by and shake things up, flinging planets at one another and potentially throwing Earth out of the Solar System altogether. Again, it’s theoretically possible, but highly unlikely.

Tardigrades laugh in the face of supernovas. (Image: NASA)

The final possibility are gamma-ray bursts. Likely caused by supernovae or hypernovae (also known as a superluminous supernova, which are about 10 times brighter than standard supernovae), these energetic explosions produce radioactive blasts capable of sterilising an entire planet. But like supernovae, gamma-ray bursts are unlikely to happen in our immediate vicinity.

With all this in mind, the researchers hypothesise that there’s a one in a million chance that a catastrophic astrophysical event will kill all forms of life on Earth—tardigrades included—before the Sun grows old enough and hot enough to boil the oceans away. Put another way, if the Sun could last forever, it would take about 10 billion years before something might wipe out the tardigrade clan.

This actually leads to a pretty optimistic conclusion.

“We do not fully understand the mechanisms by which life started, but once it exists on an Earth-like planet, the complete removal of all life (other than through evolution of the host star) is a very unlikely event,” conclude the authors in their study.

Banzai! Only until the sun turns into a bloated red giant, about seven billion years from now, will the tardigrades finally go extinct. (Image: NASA)

Loeb says these findings broaden the range of environments that are considered habitable. “Tardigrades may survive under the surface of some planets in the solar system,” he told Gizmodo. “Once they get there (for example...through the transfer of rocks from Earth to Mars), it will be difficult to kill them.”

Loeb admits, however, that his team’s analysis is based on the assumption that life is the same elsewhere as it is on Earth (the Universe may have other forms of life, with creatures even hardier than tardigrades), and that other unknown astrophysical risks might exist (a rather scary thought). Further research in these areas could clear things up.

As a final note, this study shows that life may be more common than we think. Once life gets started, it could be pretty damned hard to get rid of it. [Scientific Reports]</s>n extreme close-up of a tiny tardigrade, also known as a "water bear." A new study suggests the tiny eight-legged creatures could be the last survivors of Earth, outliving humanity.

The eight-legged micro-animal called a tardigrade could survive nearly all the way until the death of the sun, a new study suggests — long after humans are history.

The study, from Harvard and Oxford universities, detailed the threats to life on Earth over billions of years, finding that Earth-pummeling asteroids, nearby supernova blasts and gamma-ray bursts would be unlikely to completely sterilize Earth (taking out the little tardigrades in the process).

Tardigrades, which are usually less than a millimeter long (0.04 inches), are nearly indestructible, some of the most resilient forms of life on Earth. They can survive for up to 30 years without eating, and can be frozen, boiled, squished under intense pressure, and exposed to the vacuum and radiation of space without ill effect. The animal, which lives in water (and is also known as a "water bear," can survive for up to 60 years, according to a statement from the University of Oxford. [Earth's 'Alien' Creatures May Reveal Clues About Extraterrestrial Life]

"'A lot of previous work has focused on 'doomsday' scenarios on Earth — astrophysical events like supernovas that could wipe out the human race," David Sloan, a co-author on the new work and researcher at Oxford, said in the statement. "Our study instead considered the hardiest species — the tardigrade. As we are now entering a stage of astronomy where we have seen exoplanets and are hoping to soon perform spectroscopy [on those planets], looking for signatures of life, we should try to see just how fragile this hardiest life is."

"To our surprise, we found that although nearby supernovas or large asteroid impacts would be catastrophic for people, tardigrades could be unaffected," he added. "Therefore, it seems that life, once it gets going, is hard to wipe out entirely. Huge numbers of species, or even entire genera may become extinct, but life as a whole will go on."

The researchers detailed what would happen with each of those threats in a new paper, released today (July 14) in the journal Scientific Reports.

Gamma-ray bursts, the most powerful explosions in the universe, are jets of radiation likely released when a star collapses into a black hole after emitting an ultra-powerful supernova blast. If one of those blasts occurred close enough to Earth, heading straight toward the planet, it could take out Earth's ozone layer, leaving Earthlings exposed to deadly radiation levels, the researchers wrote in the paper. But life that lived below ground or in large bodies of water would be shielded from harm and could survive, including the tardigrade.

To boil away Earth's oceans, the researchers wrote, a gamma-ray burst would have to occur less than 40 light-years away, if it were aimed right toward Earth.

An ordinary, less-powerful supernova would pose the same radiation danger, but it would have to be just 0.14 light-years from Earth to vaporize the oceans and sterilize the planet. One light-year, the distance that light travels in a year, is about 6 trillion miles (10 trillion kilometers).

A killer asteroid could cloud the sky with debris, killing life that relies on sunlight, or even lead to the loss of Earth's atmosphere. But life could live on deep in the ocean, or gather sustenance from volcanic vents, the researchers said. Less than 20 known asteroids and dwarf planets, including Vesta and Pluto, would provide enough of a kick to boil off Earth's oceans with their impacts — and none are headed toward Earth anytime soon.

Calculating the probability of each of those events, and factoring in the heightened temperatures and pressures in which tardigrades can survive, the researchers found an incredibly tiny probability that an ocean-boiling, life-ending event would occur within 10 billion years.

The sun will someday evolve into a red giant star and expand to be even larger in diameter than Earth's orbit. But before that point, the star would get hot and close enough to sterilize Earth for good, boiling away the world's oceans before consuming the planet or knocking it out of orbit — ending the tardigrades' reign at last. [Death of the Sun: How It Will Destroy Earth (Infographic)]

Studies suggest that Mars once had better conditions for life, including a thicker atmosphere and lakes and streams. If life that developed on planets like Mars is anything like tardigrades, it would stick around despite the planet's current inhospitable conditions, the researchers said.

"It is difficult to eliminate all forms of life from a habitable planet," Avi Loeb, a study co-author and Harvard's chair of astronomy, said in the statement. "The history of Mars indicates that it once had an atmosphere that could have supported life, albeit under extreme conditions. Organisms with similar tolerances to radiation and temperature as tardigrades could survive long term below the surface in these conditions."

Similarly, the subsurface oceans on Saturn's moon Enceladus and Jupiter's moon Europa may feature volcanic vents that provide heat, similar to the locations where tardigrades can thrive deep under Earth's sea, he said.

"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," added Rafael Alves Batista, a co-author and researcher at Oxford. "If tardigrades are Earth's most resilient species, who knows what else is out there?"

Email Sarah Lewin at slewin@space.com or follow her @SarahExplains. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.</s>The almost-indestructible tardigrade may be able to survive on Earth even in the case of catastrophic scenarios, such as a huge asteroid hitting the planet, scientists have said. Also known as water bears, these microscopic creatures could in fact survive until the Sun dies.

Tardigrades have long intrigued scientists for their unique ability to resist a wide array of stresses that would otherwise wipe out most living species. They can live in the harshest climates and most extreme temperatures, and as such they are fascinating organisms to study as our planet undergoes profound transformations.

Learning more about tardigrades' unique abilities could be relevant in the context of the quest for extra-terrestrial life.

Indeed, to find life outside Earth, it is necessary to establish under what conditions life can emerge and subsist on a planet – there are still a lot of uncertainties surrounding this. Tardigrades manage to survive in harsh conditions, so similarly resilient organisms could also do so on other planets featuring extreme environments.

This is what a study now published in Scientific Reports argues. It shows that once life emerges, some species like tardigrades are surprisingly resilient and difficult to destroy. This opens the possibility that there might be life on other planets.

In the research, the scientists have investigated what it would take to kill tardigrades. They have considered the impact that three potential catastrophic events could have on the planet's species – a massive asteroid impact and exploding stars in the form of supernovae or gamma ray bursts.

The scientists explain that impacts of gamma-ray bursts on humans and other animals on land could potentially be disastrous as the eradication of the ozone layer would leave these species exposed to lethal levels of radiation.

But even in such an extreme scenario, life would be able to continue below the ground and tardigrades could continue to thrive. Some marine species would also manage to survive as the burst would need to be no more than 40 light-years away to boil the world's oceans - and the probability of a burst happening so close to Earth is close to zero.

Similarly, tardigrades and a number of other species would survive a supernova explosion close to Earth. The scientists also say that in order to boil the oceans, such an exploding star would need to be 0.14 light-years away. The closest star to the Sun is four light years away so the probability of a massive star exploding close enough to Earth to kill all forms of life is really low.

Finally, a large asteroid collision could lead to an "impact winter", in which the surface of the planet receives less sunlight and temperatures drop. This would be disastrous for a lot of species, including humans, which depend a lot on sunlight. However, tardigrades would probably be able to survive the drop in temperatures, and life around volcanic vents in the deep ocean life would continue.

It is also worth pointing out that asteroids large enough to cause such an effect are very rare near Earth and the possibility of them crashing on our planet is unlikely.

The study thus suggests that there are many very resilient species' on Earth including tardigrades that could survive 'doomsday scenarios'. As such, life on this planet may continue long after humans are gone, until the sun dies. It is possible that very resistant forms of life resembling tardigrades exist on exoplanets even where the environment would not be suitable for humans.

"A lot of previous work has focused on 'doomsday' scenarios on Earth - astrophysical events like supernovae that could wipe out the human race. Our study instead considered the hardiest species - the tardigrade," study author David Sloan, in the department of physics at Oxford University, said in a statement.

"As we are now entering a stage of astronomy where we have seen exoplanets and are hoping to soon perform spectroscopy, looking for signatures of life, we should try to see just how fragile this hardiest life is. To our surprise we found that although nearby supernovae or large asteroid impacts would be catastrophic for people, tardigrades could be unaffected. Therefore it seems that life, once it gets going, is hard to wipe out entirely. Huge numbers of species, or even entire genera may become extinct, but life as a whole will go on."
A newly-published paper suggests that some tardigrades may outlive most life on Earth.