Would you believe that your last drink of water could have once been used by a dinosaur? Water on earth today has been here for millions of years. Because of the hydrologic cycle (water cycle), water moves from the earth to the air to the earth again. It changes from solid to liquid to gas, over and over again. Without the water cycle, all life on earth would end. Without this never-ending cycle, plants would die, underground sources would soon be emptied, rivers and lakes and oceans would overflow and flood large areas of land (no evaporation). The whole ecologic cycle would end.