Tardigrades, known to be able to go for decades without food or water, more than all the animals on Earth they look like an alien.
Tardigrades can survive temperatures from near absolute zero to well above the boiling point of water and to direct exposure to dangerous radiations.
The far-ranging survivability of these extremophiles was tested in 2011 outside an orbiting space shuttle. They are so durable partly because they can repair their own DNA and reduce their body water content to a few percent.
Some of these miniature water-bears almost became extraterrestrials recently when they were launched toward to the Martian moon Phobos on board the Russian mission Fobos-Grunt, but stayed terrestrial when a rocket failed and the capsule remained in Earth orbit.
Tardigrades are more common than humans across most of the Earth.
Picture above, in a color-enhanced electron micrograph, a millimeter-long tardigrade crawls on moss. Credit Nicole Ottawa & Oliver Meckes / Eye of Science / Science Source Images
Tardigrades: Adorable Extremophiles