Why is the water cycle important to all life on the earth?
The water cycle is important to all life on earth for many reasons.
The water cycle is important to all life on earth for many reasons. All living organisms require water and the water cycle describes the process of how water moves through the planet.
Plants wouldn't grow without precipitation (and thus anything consuming the plants wouldn't survive and so forth). Infiltration of water filters and cleans our water. Glaciers, ice, and snow can act as stores of freshwater for both humans and other organisms. Runoff contributes to rivers, other freshwater bodies, and eventually the ocean, sustaining freshwater and marine life.
All of these process sustain life and create the ecosystems around us. Some organisms are very sensitive to changes in the water cycle. A prolonged drought can destroy a population of plants or a certain salamander species may require a set amount of soil saturation in order to avoid desiccation.
See this question on how humans use water in everyday life, this webpage from NASA on the water cycle, and this PDF on how the natural world filters water for more information on why the water cycle is so important.