Comet inspires chemistry for making breathable oxygen on Mars

Science fiction stories are chock full of terraforming schemes and oxygen generators for a very good reason—we humans need molecular oxygen (O2) to breathe, and space is essentially devoid of it. Even on other planets with ...

Army Corps approves $778M plan to block Asian carp advance

The head of the Army Corps of Engineers has sent Congress a $778 million plan to fortify an Illinois waterway with noisemakers, electric cables and other devices in the hope that they will prevent Asian carp from reaching ...

Lake Tahoe's clarity improved dramatically over past year

The famed cobalt blue waters of Lake Tahoe became more clear last year, gaining 10 feet in visibility from the year before, according to a new study released Thursday by scientists at the University of California, Davis.

Scientists investigate global spread of stinging jellyfish

"Get it off of me! Get it off of me!" shrieked Mary Carman, a marine ecologist at Woods Hole Oceanographic Institution (WHOI) as she flailed knee deep in the bath-like water of Farm Pond on Martha's Vineyard. She was observing ...

Scientists discover ancient seawater preserved from the last Ice Age

Twenty thousand years ago, in the thick of an Ice Age, Earth looked very different. Because water was locked up in glaciers hundreds of feet thick, which stretched down over Chicago and New York City, the ocean was smaller—shorelines ...

Progress in hunt for unknown compounds in drinking water

An unknown number of byproducts are formed in the drinking water treatment process, and scientists don't know what many of them are. However, using advanced technology, researchers at Linköping University have been able ...

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Water

Water is a ubiquitous chemical substance, composed of hydrogen and oxygen, that is essential for the survival of many known forms of life. In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71% of the Earth's surface. On Earth, it is found mostly in oceans and other large water bodies, with 1.6% of water below ground in aquifers and 0.001% in the air as vapor, clouds (formed of solid and liquid water particles suspended in air), and precipitation. Saltwater oceans hold 97% of surface water, glaciers and polar ice caps 2.4%, and other land surface water such as rivers, lakes and ponds 0.6%. A very small amount of the Earth's water is contained within biological bodies and manufactured products. Other water is trapped in ice caps, glaciers, aquifers, or in lakes, sometimes providing fresh water for life on land.

Water moves continually through a cycle of evaporation or transpiration (evapotranspiration), precipitation, and runoff, usually reaching the sea. Winds carry water vapor over land at the same rate as runoff into the sea. Over land, evaporation and transpiration contribute to the precipitation over land.

Clean, fresh drinking water is essential to human and other lifeforms. Access to safe drinking water has improved steadily and substantially over the last decades in almost every part of the world. There is a clear correlation between access to safe water and GDP per capita. However, some observers have estimated that by 2025 more than half of the world population will be facing water-based vulnerability. Water plays an important role in the world economy, as it functions as a solvent for a wide variety of chemical substances and facilitates industrial cooling and transportation. Approximately 70 percent of freshwater is consumed by agriculture.

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