A cosmic catastrophe of what scale must occur in order to guarantee the destruction of all life on our planet? This question was posed by a group of American astrophysicists, whose article has just been published in Scientific Reports.
It has long been known that our planet has gone through at least five periods when - for various reasons, which biologists still argue about - there was a mass extinction of plant and animal species on Earth.
The last such incident was caused, according to modern concepts, by the fall of an asteroid in the Gulf of Mexico 65 million years ago. Then about 75% of all species that existed on Earth died, including all dinosaurs. They were destroyed by giant tsunamis and a global winter caused by emissions of smoke and ash into the atmosphere.
However, now scientists have come to the conclusion that for the complete sterilization of our planet, a catastrophe of a much larger scale and the complete evaporation of the oceans will be required.
“They posed the grand question - how sustainable is organic life in general? - and translated it into the language of equations, having carried out the appropriate calculations: how much energy is needed to boil the entire World Ocean? - explains astrophysicist and exoplanet specialist at Princeton University Joshua Wynn, who was not involved in the study itself.
First of all, the authors calculated the amount of energy required to heat all the water on Earth above 100 degrees Celsius. It was 6 x 10 to the 26th power of joules, which is about a million times the annual energy consumption of all mankind.
Then they started looking for space objects that could cause such a disaster.
Scientists have come to the conclusion that a collision of the Earth with a giant asteroid of the Vesta or Pallas class could cause such a catastrophe. Another couple of candidates for the role of the killer of all life on our planet in this way is a supernova explosion or a sharp burst of gamma radiation of cosmic origin.
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However, the likelihood of any of these events is extremely small, notes one of the study authors Avi Loeb of Harvard University. The fact is that asteroids of this type never approach the Earth, but revolve in almost perfectly circular orbits between Mars and Jupiter.
A supernova explosion could indeed deprive the Earth of the atmosphere and hydrosphere, but for this it would have to happen near the outer edge of the solar system, at a distance of only 0.13 light years. That is, more than 30 times closer than to the closest star to us, which can claim to be a supernova.
The researchers then asked the question - are there any species on earth that have a chance to survive even such a disaster?
It turned out that microscopic invertebrates from the tardigrade type are theoretically capable of this. They can withstand a temperature of -20 ° C for 30 years, can remain alive for 20 months in liquid oxygen at -193 ° C, and even survive eight hours of cooling with liquid helium to -271 ° C; in addition, they can withstand heating up to 60-65 ° С for 10 hours and up to 100 ° С for an hour, as well as many months of exposure to hard gamma rays.
However, even these largely mysterious creatures cannot exist indefinitely on a planet without a drop of water.
This research is not as speculative as it might seem at first glance.
According to one of the authors of the article, Oxford University astronomer David Sloan, the search for habitable exoplanets requires criteria that can indicate the possibility of organic life. Now these criteria can be revised towards expansion.
He believes that life on Earth is an extremely stable phenomenon, capable of surviving almost any troubles such as global warming or nuclear war, which may result from human activities.