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Last survivors on Earth?

Scientists say they’re likely to be tardigrades – tiny, 8-legged marine creatures – which can survive until the sun dies, long after we humans have disappeared.

Image via Eye of Science.

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.

Water bear (tardigrade), image captured with a scanning electron micrograph, via Bob Goldstein and Vicky Madden.

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.

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Eleanor Imster

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