Water blankets approximately 71% of Earth’s surface. This ubiquitous compound, composed of two hydrogen atoms and one oxygen atom, forms the foundation for many natural processes. Its presence shapes the physical environment and supports the intricate web of life on Earth.
Where Water Resides and Its Forms
Water exists in various natural reservoirs across Earth, with the vast majority residing in oceans. About 97% of the planet’s water is saltwater. Freshwater makes up a much smaller percentage, with a significant portion locked away in glaciers and ice caps, particularly in polar regions and high mountains.
Surface freshwater sources, such as rivers, lakes, and wetlands, contain a relatively small fraction of Earth’s total water. A substantial amount of freshwater is also stored underground as groundwater. The atmosphere holds water in gaseous form, and living organisms also contain water within their tissues.
Water appears in three states: solid, liquid, and gas. As a solid, it forms ice in glaciers, ice caps, and frozen lakes, rivers, and ground. The liquid state is the most common, found in oceans, lakes, rivers, and as rain. Water also exists as water vapor in the atmosphere.
The Continuous Journey of Water
Water undergoes a constant movement known as the hydrological cycle. This journey begins with evaporation, where solar energy transforms liquid water from oceans, lakes, and rivers into water vapor. Plants also contribute to this atmospheric moisture through transpiration, releasing water vapor from their leaves.
As water vapor rises into the cooler atmosphere, it undergoes condensation, forming tiny water droplets or ice crystals. These droplets or crystals aggregate to form clouds. When these clouds become saturated, the water returns to Earth as precipitation, which can take the form of rain, snow, sleet, or hail.
Upon reaching the Earth’s surface, precipitation either soaks into the ground to become groundwater or flows over the land as runoff. This runoff often collects into streams and rivers, eventually making its way back to lakes and oceans. This continuous circulation ensures water is constantly redistributed across the planet, sustaining various environments.
Water’s Important Role for Life
Water serves as the universal solvent within living organisms, facilitating countless biochemical reactions necessary for life. It transports nutrients and oxygen to cells while carrying away waste products. For plants, water is a reactant in photosynthesis, the process by which they convert light energy into chemical energy, forming the base of most food webs.
Animals rely on water for hydration, temperature regulation, and as a medium for bodily fluids like blood. Aquatic ecosystems, such as oceans, lakes, and rivers, are entirely dependent on water as the habitat for diverse species. The availability of clean water directly influences the biodiversity and productivity of these environments.
Beyond individual organisms, water shapes landscapes and influences Earth’s climate. Rivers carve valleys, glaciers sculpt mountains, and oceans regulate global temperatures by absorbing and distributing heat. The presence and movement of water sustain wetlands, forests, and deserts, each with unique flora and fauna adapted to specific water conditions.
The Unique Properties of Water
Water exhibits several unique properties that make it well-suited for its roles in nature. Its polarity, meaning it has a slight positive charge on one end and a slight negative charge on the other, allows it to form hydrogen bonds with other water molecules. This strong attraction contributes to water’s cohesive nature, allowing it to move upward in plant stems through capillary action.
This polarity also makes water an excellent solvent, often called the “universal solvent.” This property is important for transporting nutrients in biological systems and weathering minerals in geological processes. Water’s ability to dissolve a wide range of compounds allows for complex chemical interactions in both living and non-living systems.
Water possesses a high specific heat capacity, meaning it can absorb or release large amounts of heat energy with only a small change in its own temperature. This property helps moderate Earth’s climate, preventing extreme temperature swings, particularly near large bodies of water. The oceans, in particular, act as vast heat reservoirs, absorbing solar radiation and slowly releasing it.
Another unique property is water’s density anomaly: its solid form, ice, is less dense than its liquid form. This causes ice to float on water, preventing entire bodies of water from freezing solid from the bottom up. This floating ice layer insulates the water below, allowing aquatic life to survive through cold periods.