If a large enough asteroid smashes into the Earth, it would throw billions of tons of rock and ash into the air, which would block out the Sun and turn our planet into a frigid desert. The death toll would be catastrophic, and humanity would certainly be doomed. But among the few survivors would likely be the microscopic tardigrade.
What would it take to kill these tiny animals? Quite a lot, according to new research that predicts how life would react to disasters from space.
“Tardigrades are as close to indestructible as it gets on Earth,” astrophysicist Rafael Alves Batista tells Casey Smith of National Geographic. The phylum has existed for at least 520 million years, through multiple mass extinctions. Their hardiness means they can endure deadly radiation, temperatures ranging from 212 degrees Fahrenheit to 459 degrees below zero, deep pressures below the ocean, being dried out for a decade, and even the vacuum of space.
Using mathematical modeling, Batista and his collaborators decided to try their best to predict what kinds of horrific disasters could actually wipe out even the gritty tardigrade. More than being just a thought experiment, reports George Dvorsky for Gizmodo, these simulations can help show what kinds of places could theoretically sustain life in other parts of the Solar System.
“This can guide us in which environments we should not search for life," astronomer Avi Loeb tells Dvorsky.
In their study published today in the journal Scientific Reports, the researchers conclude that the only way the tardigrades could be wiped out is if Earth's oceans are boiled away. They looked at three potential space-related disasters that could accomplish this devastating end: an impact from a massive asteroid, a supernova from a large star, or gamma radiation hitting Earth.
“These are the biggest ways you can transfer energy to the planet,” astrophysicist David Sloan tells Ben Guarino of The Washington Post. If any of these events boiled away Earth's oceans, even the tardigrades would eventually perish without any source of food or water or air.
Thankfully for the tardigrades (not to mention us), the scientists calculated that the chances of these events actually happening is extremely low. There are few asteroids in our Solar System large enough that they would boil away Earth's water if they struck our planet, reports Giorgia Guglielmi for Science, and none of them are heading anywhere Earth. There are also no stars close enough to Earth capable of going supernova, which is when stars explode brightly in a final gasp before dying. And gamma ray bursts of radiation, thought to be released by stars going supernova, are unlikely to occur at strengths high enough to strip away Earth's water in our corner of the galaxy.
Thus, the study concludes, there's just about a one in million chance of an event completely sterilizing Earth. So it seems likely that it will take the death of our Sun to finally end the long journey of the tardigrades.
“It seems that life, once it gets going, is hard to wipe out entirely,” Sloan tells Smith. “Huge numbers of species, or even entire genera, may become extinct, but life as a whole will go on.”