Tardigrades are some of the toughest but least well-known creatures on our planet. These tiny animals, also called moss piglets or water bears, are definitely of this earth, but some can boast that they've also traveled to space.
They have been found in the fossil record as long ago as the middle of the Cambrian Period, over 500 million years ago, when complex animals were evolving. Over 1,000 species of tardigrade exist, in places as diverse as the depths of the ocean and the tops of the tallest mountains. For example, researchers have found them at ocean depths of over 10,000 feet — that's nearly two miles down — in the Antarctic, and at the highest altitudes of the Himalayas.
You can even find tardigrades in your backyard; Just look in semi-aquatic habitats, such as where water collects on and under leaves, and especially in mosses. But you aren't likely to see them with your naked ey, since these almost cute pudgy micro-animals are usually only about 1 mm long.
They have eight legs that curl inwards terminating in ferocious claws. Under a microscope, their dagger-like teeth look pretty scary, but humans and most other animals have nothing to fear because they mostly feed by sucking the juices from moss, lichen, and algae. Some tardigrade eat even smaller animals, including other tardigrades.
When faced with an adverse environment, like extreme heat or cold, they expel almost all of their water and become a dried barrel called a "tun."
Their metabolism nearly stops, but they are not dead. Tardigrades can come back to life after extreme conditions that would kill nearly every other living organisms — earning them the name "extremotolerant."
Tardigrades have been boiled and frozen and come back to life. They survive at temperatures between -458°F to a scorching 303°F.
Scientists found unique proteins in tardigrades that don't have a shape when they are in the presence of water, but when they dry out in a process called desiccation, they form a glass-like matrix. The matrix has pores that trap proteins that are sensitive to desiccation, preventing them from clumping up and becoming unusable. When the tardigrade gets wet, the process reverses, and the tardigrade comes back to life.
Where 5–10 grays (Gy) of radiation would be fatal to a human, tardigrades can withstand about 5,000 Gy. Recently, scientists discovered a protein called Dsup in tardigrade that prevents the destruction of its DNA by radiation. Inserting part of the animal's genome involved in producing Dsup into mammalian cells in a test tube reduces DNA damage caused by X-rays in those cells by about 40 percent.
In 2007, tardigrades hitched a ride on the FOTON-M3 spacecraft as it was launched into a low-Earth orbit for ten days. Tardigrades exposed to space vacuum came back to life on Earth, and some of them recovered, even after combined exposure to space vacuum and radiation from the Sun.
"No animal has survived open space before. The finding that animals survived rehydration after ten days in open space — and then produced viable embryos as well — is really remarkable, " developmental biologist Bob Goldstein, of the University of North Carolina at Chapel Hill, told New Scientist.
Slowly, these mysterious tardigrades are giving up the secrets of their survival that allowed them to outlive the big five extinction events and the lifetime of dinosaurs on Earth.
Scientists have unraveled some of the physiologic processes behind their awe-inspiring abilities. But we know there is a lot more to be discovered, and some may prove useful to us mere mortals.