The water cycle makes life on Earth possible. And what makes it possible are the incredible properties of water itself.

Earth is the only planet we know of where the three phases of water—solid, liquid, and gas—are present on its surface.

That’s partly because those three phases exist in a narrow temperature window. And the middle phase—liquid water—corresponds to much of Earth’s surface temperature.

This allows our oceans to exist, which are the key reservoirs of the hydrological system. Winds moving across oceans lift huge volumes of water vapor—seven times more than simple evaporation could.

Converting liquid water to gas distills it, leaving salts and impurities in the sea and carrying pure water vapor into the atmosphere. It rises to form clouds and rains down elsewhere.

Three-quarters of that rain falls back into the ocean. The other 25 percent falls on land, where it’s used by all terrestrial life.

But it’s also one of the most powerful forces eroding the surface of Earth.

Gravity pulls rainwater downhill, and over a few million years—a blink of an eye on Earth’s time scale—it can flatten mountains and carry them in rivers, grain by grain, to the sea.

If frozen into glaciers, water becomes a river of ice and rock, grinding down the earth even faster.

The amazing life-giving, planet-shaping properties of water are what make Earth what it is, and we’ll talk a lot more about it on EarthDate.