Although all organisms need water, some species have been found to have special adaptations that allow them to survive when water is scarce. Endoliths are unicellular organisms that live inside rocks. They use the tiny amounts of water that fill the small spaces between minerals in the rock. The discovery of endoliths makes scientists hopeful that humans might someday find life on other planets.Other organisms have found ways to survive dry spells. When water is scarce, some organisms replace the water in their cells with sugars, maintaining the shape of the cells. They can remain in this state of suspended animation for years, even centuries. When water is once again available, the sugars dissolve, and the organism revives. This is common in lichens and mosses but also occurs in other plants, fungi, bacteria, and animals such as tardigrades.