The molecular species have very different functions: The free H 2 O molecule is transferred across the air-sea interface, and the H 2 O 5 species absorbs sound and, by interleaving with its neighbor pentamers, accounts for the compressibility of water.
The presence of sea salts adds some complexity, and the case for the freshwater bodies of the world is a little easier to treat. But overall, Earth scientists now have a new quantitative tool to gain insights into problems as diverse as the consequences of warming of lakes and oceans and the transport of water across cellular membranes. Underwood, E.
Published on 02 May The authors. Any reuse without express permission from the copyright owner is prohibited. Iddris et al. Skip to content The majority of seawater is made up of clusters of five H 2 0 molecules. Lakes and other reservoirs counteract fluctuations in river flow from one season to the next because they store large amounts of water. Lakes contain by far the largest amount of fresh surface water. River flows can vary greatly from one season to the next and from one climatic region to another.
In tropical regions, large flows are witnessed year round, whereas in drylands , rivers are often ephemeral and only flow periodically after a storm. Past data records for river flow and water levels help to predict yearly or seasonal variations, though it is difficult to make accurate longer-term forecasts. Some records in industrialised countries go back up to years. By contrast, many developing countries started keeping records only recently and data quality is often poor. Many wetlands were destroyed or converted to other uses during the last century.
Those that remain can play an important role in supporting ecosystems , preventing floods, and increasing river flows. Ninety-six percent of liquid fresh water can be found underground. Groundwater feeds springs and streams, supports wetlands, helps keep land surfaces stable, and is a critical water resource.
Hundreds of cities around the world, including half of the very largest, make significant use of groundwater. This water can be especially useful during shortages of surface water. Groundwater aquifers vary in terms of how much water they hold, their depth, and how quickly they replenish themselves. The variations also depend on specific geological features. Just what is it about water, specifically liquid water, that makes it essential for life?
The short answer is that life on Earth requires it. Photosynthetic life snatches the hydrogen from water molecules to make sugars. Organisms use water to add rigidity to cells and transport nutrients. If we don't drink it, we die. But it's the handful of intrinsic—and collectively unique—properties that explains why water is the elixir of life. Sushil Atreya, who studies the formation of planets and the evolution of their atmospheres at the University of Michigan at Ann Arbor's Planetary Science Laboratory, breaks it down this way: "Liquid water acts as a solvent, as a medium and as a catalyst for certain types of proteins, and those are three main things that allow life to flourish," he says.
Liquid water's property as a solvent, in which salts and organic compounds such as amino acids and sugars readily dissolve, is due to its dipole molecular structure. The oxygen atoms in water hold their electrons much more strongly than the hydrogen atoms do, so they accumulate a negative electrical charge.
Water's hydrogen atoms, bent on the same side of the water molecule, are positively charged. The resulting structure is the reason why water molecules can break down such a wide variety of chemical species.
Although it's a superior solvent, water also provides an ideal medium in which chemical reactions can occur and nutrients can be easily transported, Atreya says. That includes enzymes, essential to life processes, which need water in order to do their job. A few other properties make water the ideal medium for life: Water can remain a liquid over a wide range of temperatures, from zero degree Celsius to degrees C—and even wider if dissolved salts and gases, such as ammonia, are added.
The range also varies with pressure. Also, ice floats. Frozen water is less dense than its liquid form because "when you make a crystal, arranging atoms in an ordered repeating pattern, you just can't stack them very tightly," Conrad says.
The difference in density between the solid and liquid states of water means that ice sheets can cover oceans, protecting life below.
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