Why is this the answer?

The answer is water because this clever riddle describes the three different forms that water can take! Water is unique because it can exist naturally in all three forms on Earth. Scientists call these forms "states of matter": liquid, gas, and solid. The first line, "Three lives have I," is the key. These three lives are liquid water, solid ice, and gaseous water vapor. The second clue, "Gentle enough to soothe the skin," refers to water in its liquid state. This is the water you are most familiar with. When you take a drink, swim in a pool, or wash your face, the water is gentle and soothing. It feels soft and cool and is necessary for all living things. Liquid water is kind and keeps our bodies and the world around us clean and healthy. The third clue, "Light enough to caress the sky," describes water in its gas form, which we call water vapor. When water is heated, it turns into an invisible gas and rises high into the atmosphere. The water vapor is so light that it floats. When this vapor cools down, it groups together to form clouds. Clouds are like light, soft, gentle puffs of water floating in the air, seeming to touch or "caress" the sky. The final clue, "Hard enough to crack rocks," talks about water in its solid state: ice. When water freezes, it expands. Imagine water seeping into a small crack in a rock. When that water turns into ice, it expands with such great force that it can split the rock apart. Giant masses of ice, like glaciers, are also hard and strong enough to carve out valleys and mountains over long periods of time. In its solid life, water shows incredible strength and power. This makes water the perfect answer, as it is the only thing that can be gentle, light, and hard, all in its different forms.