Water-dwelling, eight-legged, segmented micro-animals called tardigrades 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, according to new research from the Universities of Oxford and Harvard.
This scanning electron microscope image shows a tardigrade. Image credit: Diane Nelson, National Park Service, U.S. Department of the Interior.
Tardigrades were first discovered in 1773 by the German zoologist Johann August Ephraim Goeze.
Also known as water bears or moss piglets, they can live for up to 60 years, and grow to a maximum size of 0.5 mm, best seen under a microscope.
These creatures are able to survive for up to 30 years without food or water, for a few minutes at temperatures as low as minus 272 degrees Celsius (minus 457 degrees Fahrenheit) or as high as 150 degrees Celsius (302 degrees Fahrenheit), and minus 20 degrees Celsius (minus 4 degrees Fahrenheit) for decades.
They withstand pressures from virtually 0 atm in space up to 1,200 atm at the bottom of the Marianas Trench, and are also resistant to radiation levels up to 5,000-6,200 Gy (Gray, unit of radiation dose).
Now, a team of Oxford and Harvard researchers has found that tardigrades survive all astrophysical calamities, such as an asteroid, since they will never be strong enough to boil off the world’s oceans.
“It is difficult to eliminate all forms of life from a habitable planet,” said Professor Abraham Loeb, Chair of the Astronomy Department at Harvard University and co-author of the paper discussing the results in the journal Scientific Reports.
“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.”
Three potential astrophysical events were considered as part of the research: large asteroid impacts, supernovae and gamma ray bursts.
“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,” Professor Loeb and co-authors said.
“Gamma-ray bursts and supernovae can be deadly due to the lethal doses of radiation and in particular the shock wave associated with the burst. Radiation can cause the depletion of the ozone layer, removing the shield that protects us from cosmic radiation.”
“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 roughly 4 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 supernovae, they 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.”
“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 lead author Dr. Rafael Alves Batista, postdoctoral research associate in the Department of Physics at Oxford University.
“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.”
“To our surprise we found that although nearby supernovae or large asteroid impacts would be catastrophic for people, tardigrades could be unaffected,” added co-authors Dr. David Sloan, postdoctoral research associate in the Department of Physics at Oxford University.
“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.”
“Without our technology protecting us, humans are a very sensitive species. Subtle changes in our environment impact us dramatically,” Dr. Batista said.
“There are many more resilient species’ on Earth. Life on this planet can continue long after humans are gone.”
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David Sloan et al. 2017. The Resilience of Life to Astrophysical Events. Scientific Reports 7, article number: 5419; doi: 10.1038/s41598-017-05796-x
