why is earth called blue planet
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Answer:
Earth is the only planet in our solar system that has a large amount of liquid water. About 74% of the surface of Earth is covered by liquid or frozen water. Because of this, people sometimes call it the blue planet. Because of its water, Earth is home to millions of species of plants and animals.
Planet Earth has been called the "Blue Planet" due to the abundant water on its surface. Here on Earth, we take liquid water for granted; after all, our bodies are mostly made of water. However, liquid water is a rare commodity in our solar system. No liquid water has been confirmed in our solar system, but it is likely that Jupiter's moon Europa and Saturn's moon Enceladus have liquid oceans under a frozen crust. Nor has a drop of water been observed yet in interstellar space. Only a planet of the right mass, chemical composition, and location can support liquid water. And only on such planets could life as we know it flourish.
Liquid water covers most of the surface of our planet. This water comes in many forms, each with it's own special properties. Rain is essentially pure water (consisting only of H2O with trace amounts of elements and other compounds picked up from atmospheric dust), while fresh spring water and most lakes and rivers contain more dissolved salts (~0.02-0.4 percent %, or parts per hundred,). Ocean water is much more salty and has on average ~3.5% salt content, also referred to as "salinity". Note that 3.5% equals 35 parts per thousand (ppt) which is the typical unit for which salinity is reported, and this value equals 35,000 parts per million (ppm) - a ppt is equal to 1 gram of salt dissolved into 1000 grams of water, or a gram per kilogram (g/kg). Some spring and lake waters are even saltier than the ocean, and they are often called "brines" which can become saturated with salts. These different types of water are found in many different environments on Earth.