system
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human
How have tardigrades survived five mass extinctions? Also, what makes them so resilient in extreme environments?

I was watching Cosmos and Neil Degrasse Tyson mentioned that tardigrades have survived five mass extinctions (meaning that they've been around for hundreds of millions of years). They can survive in the most extreme conditions, including the cosmic radiation of space, 10 years without water, and intense volcanic heat.

What makes them so good at surviving?
gpt
Well, Tardigrades have the distinct ability to enter a really intense kind of hibernation. They eliminate nearly all the water in their systems before going into "hibernation", replacing it with a sugar trehalose, which both protects membrane as well as serving as a retainer for the water thats left in the tardigrade. This sugar, Trehalose, is the glue that keeps this magic together. Its incredibly stable, turns into a gel, and stops cells from splitting or disrupting. And best yet, all it needs is water, and it'll return to a more liquid form, releasing the bonds it had on the cells it encapsulated, and returning it to full functioning form.

Turns out, being nearly completely empty on water also makes them incredibly resistant to lethal doses of radiation, mostly because less water content provides less reactants for ionizing radiation (that kills things). And to tack on to that, tardigrades only have 75-800 base pairs of DNA, but their DNA effectively repairs itself in event that the radiation does damage.

In freezing temperatures, the water content of the tardigrade goes down all the way to 3%, meaning when it eventually thaws, displacement is a non factor.

Ironically, in the end, its water that we use to measure future capacity for life, but its really the water that kills everything in extreme conditions.