Water
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Essential liquid for life on Earth
Water is a clear, colorless liquid that is essential for life on Earth. It makes up oceans, rivers, lakes, and clouds, and it is found in the ground, in the air, and inside living things. Most plants and animals need water to survive, and humans use it for drinking, growing food, cleaning, and many other purposes.
Water exists in three main forms, or states: solid, liquid, and gas. Liquid water is found in seas, lakes, and rain. Solid water appears as ice or snow, usually in cold regions or higher elevations. Water vapor, the gas form, is present in the air and forms clouds when it cools. Water can change between these states depending on temperature. For example, freezing turns liquid water into ice, and evaporation changes liquid water into vapor.
A key part of understanding water is the water cycle. This cycle describes how water moves through the environment. Water evaporates from oceans, lakes, and soil, and rises into the air as vapor. It then cools and condenses to form clouds. When the clouds become heavy, water falls back to Earth as rain, snow, or other forms of precipitation. This water collects in rivers and oceans or soaks into the ground, and the cycle begins again.
Earth has both freshwater and saltwater. About most of Earth's water is in the oceans, where it contains dissolved salts. Freshwater is found in rivers, lakes, ice caps, and underground spaces called aquifers. Although freshwater makes up only a small part of all water on Earth, it is the main source used for drinking, farming, and many daily needs.
Water also shapes Earth's surface. Flowing water can wear down rocks and carry sediments, creating valleys, canyons, and riverbeds. Ice can carve landscapes as glaciers move slowly across land. Waves and currents shape coastlines over long periods of time. These processes help form many natural features.
Living things depend on water for basic functions. Plants use water to move nutrients through their stems and leaves. Animals need water for digestion, temperature control, and transporting nutrients in their bodies. Humans use water in homes, industries, and agriculture. Because water is so important, scientists study how it flows, how much is available, and how it changes in different environments.
Water exists in three main forms, or states: solid, liquid, and gas. Liquid water is found in seas, lakes, and rain. Solid water appears as ice or snow, usually in cold regions or higher elevations. Water vapor, the gas form, is present in the air and forms clouds when it cools. Water can change between these states depending on temperature. For example, freezing turns liquid water into ice, and evaporation changes liquid water into vapor.
A key part of understanding water is the water cycle. This cycle describes how water moves through the environment. Water evaporates from oceans, lakes, and soil, and rises into the air as vapor. It then cools and condenses to form clouds. When the clouds become heavy, water falls back to Earth as rain, snow, or other forms of precipitation. This water collects in rivers and oceans or soaks into the ground, and the cycle begins again.
Earth has both freshwater and saltwater. About most of Earth's water is in the oceans, where it contains dissolved salts. Freshwater is found in rivers, lakes, ice caps, and underground spaces called aquifers. Although freshwater makes up only a small part of all water on Earth, it is the main source used for drinking, farming, and many daily needs.
Water also shapes Earth's surface. Flowing water can wear down rocks and carry sediments, creating valleys, canyons, and riverbeds. Ice can carve landscapes as glaciers move slowly across land. Waves and currents shape coastlines over long periods of time. These processes help form many natural features.
Living things depend on water for basic functions. Plants use water to move nutrients through their stems and leaves. Animals need water for digestion, temperature control, and transporting nutrients in their bodies. Humans use water in homes, industries, and agriculture. Because water is so important, scientists study how it flows, how much is available, and how it changes in different environments.
What We Can Learn
- Water exists as solid, liquid, and gas
- The water cycle describes how water moves through the environment
- Freshwater is limited and important for daily use
- Water shapes landforms through erosion and movement
