Researchers found that a complete destruction of life on Earth is practically impossible thanks to indestructible extremophiles like the tardigrades. The implications of their findings go beyond Earth creatures' capability to survive extreme astrophysical events.
Indestructible Water Bears
To see just how resilient Earth's creatures are and whether it's possible to completely sterilize the planet, researchers looked into just how tardigrades, the planet's hardiest creatures, would react to three hypothetical cataclysmic astrophysical events.
What are tardigrades anyway? Tardigrades are eight-legged creatures that are practically indestructible. For starters, tardigrades are extremophiles, which means that they are capable of surviving in extreme conditions.
They can survive minutes in freezing -272 degrees Celsius or in scalding 150 degrees Celsius, and can stay alive for decades in -20 degrees Celsius. They also have the capability to withstand space's 0 atm pressure up to the 1,200 atm of the Mariana's Trench.
Tardigrades aren't even done yet because they can also withstand radiation levels of up to ~5,000 to ~6,200 Gy. If that's not enough, they can also be pretty cute, which is why they are often called water bears. All that hardiness is packed into a microscopic creature that can only grow up to 0.5 millimeter.
Cataclysmic Astrophysical Events
According to the researchers, without our development of technology, humans are actually a pretty fragile species. It is because of this that they decided to instead focus on the three events that could potentially kill the planet's hardiest creatures.
To test the survival capabilities of tardigrades, researchers from the Universities of Oxford and Harvard considered three potential life-destroying calamities that could hit the Earth: an asteroid impact, supernova, and gamma-ray bursts.
In the case of asteroids, researchers surmise that for an asteroid to be hot enough to boil the oceans and kill tardigrades, it would need to have a mass of at least ∼1.7 × 1018 kg. There are currently only 17 asteroids plus a few dwarf planets that are of sufficient mass to elicit such a reaction.
However, at least in the current knowledge, there are no known asteroids or dwarf planets that are positioned to intersect with the Earth's orbit to be a threat to tardigrades. Even in the event of an "impact winter" when temperatures significantly drop, extremophiles in the deepest parts of the oceans will remain unaffected.
For a supernova to be deadly to tardigrades, it would have to be at a distance of 0.14 light-years away, which is much closer than the closest stars to our solar system, Proxima Centauri. Fortunately, the Earth is in a comfortable position where the nearest potential supernova is three magnitudes farther than the estimated distance for sterilization. Therefore, it is very unlikely for a supernova to wipe out all life on Earth in the sun's lifetime.
Gamma-Ray bursts, if close enough, are disastrous to humans and other land-based animals due to the eradication of the ozone layer, thereby leaving us exposed to extreme radiation. However, this is not the case for marine species. In fact, even a complete loss of atmosphere would likely not affect the species living on the ocean floor.
Essentially, what the researchers are implying is that it is practically impossible to completely annihilate all life on Earth, and a large part of that resilience is thanks to extremophiles like tardigrades. Even if humans go extinct, the Earth will always have life forms to continue its cycle.
Another important implication of this study is the fact that it also provides insight into the possibilities of life on other planets. With creatures on Earth such as tardigrades, it shows that it is not unlikely for other planets to harbor life that thrive in extreme conditions.
The study is published in the journal Scientific Reports.