Tardigrades are probably the most paradoxical animals on the planet. On the one hand, these microscopic organisms are impossibly cute, seeming like tiny blimps that bumble around harmlessly on their stubby legs. But they also enjoy a legendary reputation as the toughest, most indestructible creatures on Earth.
Just 0.04 inches (1 millimeter) long (or less), their little bodies contain biological superpowers that help them withstand conditions that would spell certain death for other organisms. Taking their toughness into account, how long can these creatures live?
Many researchers have gone to extreme lengths to test tardigrade resilience, by blasting them (in their tun state) into space. In many of these studies, the space-traveling tardigrades were exposed to direct solar radiation and gamma-rays. But when they were popped into a water-filled petri dish back on Earth, they “basically walked away and said, ‘OK, where’s dinner?'” McInnes said. Tardigrades are seemingly able to resist radiation and even repair their DNA, which may explain why they’re so resilient to radiation’s extreme effects, a 2013 PLOS ONE study reported.
“If they’ve got this ability to last over time, how long do they live? Well, how long is a piece of string?” McInnes said. But she cautioned against the prevailing belief that tardigrades are invincible: “They can’t live forever,” she said. The widely publicized notion that tardigrades can survive in a tun state for 100 years or more is an overstatement, for instance. And high-stress living does take its toll on their physiology. Only some tardigrades survive the torments of experimental freezing, boiling and radiation that we humans subject them to.
But there is another way to appreciate their resilience: on a species level. Not only have tardigrades existed since the Cambrian period 541 million years ago, but they may well go on to outlive us — and probably all other life on Earth, according to a 2017 paper published in the journal Scientific Reports. It found that if a cataclysmic event like an asteroid impact were to befall Earth and destroy life, a group of tardigrades inhabiting the ocean’s Mariana Trench would endure.