Which two statements best describe the source of the water in earths oceans? pick two answers.

seawater, water that makes up the oceans and seas, covering more than 70 percent of Earth’s surface. Seawater is a complex mixture of 96.5 percent water, 2.5 percent salts, and smaller amounts of other substances, including dissolved inorganic and organic materials, particulates, and a few atmospheric gases.

Seawater constitutes a rich source of various commercially important chemical elements. Much of the world’s magnesium is recovered from seawater, as are large quantities of bromine. In certain parts of the world, sodium chloride (table salt) is still obtained by evaporating seawater. In addition, water from the sea, when desalted, can furnish a limitless supply of drinking water. Many large desalination plants have been built in dry areas along seacoasts in the Middle East and elsewhere to relieve shortages of fresh water.

water scarcity

Members of the New Zealand Defence Force pumping seawater into holding tanks on Funafuti Atoll for later desalination in an attempt to alleviate significant freshwater shortages in Tuvalu, 2011.

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The six most abundant ions of seawater are chloride (Cl−), sodium (Na+), sulfate (SO24−), magnesium (Mg2+), calcium (Ca2+), and potassium (K+). By weight these ions make up about 99 percent of all sea salts. The amount of these salts in a volume of seawater varies because of the addition or removal of water locally (e.g., through precipitation and evaporation). The salt content in seawater is indicated by salinity (S), which is defined as the amount of salt in grams dissolved in one kilogram of seawater and expressed in parts per thousand. Salinities in the open ocean have been observed to range from about 34 to 37 parts per thousand (0/00 or ppt), which may also be expressed as 34 to 37 practical salinity units (psu).

Inorganic carbon, bromide, boron, strontium, and fluoride constitute the other major dissolved substances of seawater. Of the many minor dissolved chemical constituents, inorganic phosphorus and inorganic nitrogen are among the most notable, since they are important for the growth of organisms that inhabit the oceans and seas. Seawater also contains various dissolved atmospheric gases, chiefly nitrogen, oxygen, argon, and carbon dioxide. Some other components of seawater are dissolved organic substances, such as carbohydrates and amino acids, and organic-rich particulates. These materials originate primarily in the upper 100 metres (330 feet) of the ocean, where dissolved inorganic carbon is transformed by photosynthesis into organic matter.

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Many of the characteristics of seawater correspond to those of water in general, because of their common chemical and physical properties. For example, the molecular structure of seawater, like that of fresh water, favours the formation of bonds among molecules. Some of the distinctive qualities of seawater are attributable to its salt content. The viscosity (i.e., internal resistance to flow) of seawater, for example, is higher than that of fresh water because of its higher salinity. The density of seawater also is higher for the same reason. Seawater’s freezing point is lower than that of pure water, and its boiling point is higher.

San Francisco International Airport has a “wag brigade”—a pack of therapy dogs available to calm nervous fliers. Joining the comfort canines is LiLou, a therapy pig.

hydrosphere, discontinuous layer of water at or near Earth’s surface. It includes all liquid and frozen surface waters, groundwater held in soil and rock, and atmospheric water vapour.

Water is the most abundant substance at the surface of Earth. About 1.4 billion cubic km (326 million cubic miles) of water in liquid and frozen form make up the oceans, lakes, streams, glaciers, and groundwaters found there. It is this enormous volume of water, in its various manifestations, that forms the discontinuous layer, enclosing much of the terrestrial surface, known as the hydrosphere.

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Follow water as it cycles through the air, land, lakes and rivers, and oceans

Overview of water moving through the hydrologic cycle, or water cycle: it evaporates from Earth's surface as water vapour, which condenses in the atmosphere, forming clouds and precipitation, which falls to the land and flows through lakes, rivers, and oceans, from which water evaporates as the cycle repeats.

Central to any discussion of the hydrosphere is the concept of the water cycle (or hydrologic cycle). This cycle consists of a group of reservoirs containing water, the processes by which water is transferred from one reservoir to another (or transformed from one state to another), and the rates of transfer associated with such processes. These transfer paths penetrate the entire hydrosphere, extending upward to about 15 km (9 miles) in Earth’s atmosphere and downward to depths on the order of 5 km (3 miles) in its crust.

hydrologic cycle

This diagram shows how, in the hydrologic cycle, water is transferred between the land surface, the ocean, and the atmosphere.

This article examines the processes of the water cycle and discusses the way in which the various reservoirs of the hydrosphere are related through the water cycle. It also describes the biogeochemical properties of Earth’s waters at some length and considers the distribution of global water resources and their use and pollution by human society. Details concerning the major water environments that make up the hydrosphere are provided in the articles ocean, lake, river, and ice. See also climate for specific information about the impact of climatic factors on the water cycle. The principal concerns and methods of hydrology and its various allied disciplines are summarized in Earth sciences.

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Ocean waters and waters trapped in the pore spaces of sediments make up most of the present-day hydrosphere. The total mass of water in the oceans equals about 50 percent of the mass of sedimentary rocks now in existence and about 5 percent of the mass of Earth’s crust as a whole. Deep and shallow groundwaters constitute a small percentage of the total water locked in the pores of sedimentary rocks—on the order of 3 to 15 percent. The amount of water in the atmosphere at any one time is trivial, equivalent to roughly 13,000 cubic km (about 3,100 cubic miles) of liquid water, or about 0.001 percent of the total at Earth’s surface. This water, however, plays an important role in the water cycle.

At present, ice locks up a little more than 2 percent of Earth’s water and may have accounted for as much as 3 percent or more during the height of the glaciations of the Pleistocene Epoch (2.6 million to 11,700 years ago). Although water storage in rivers, lakes, and the atmosphere is small, the rate of water circulation through the rain-river-ocean-atmosphere system is relatively rapid. The amount of water discharged each year into the oceans from the land is approximately equal to the total mass of water stored at any instant in rivers and lakes.

Soil moisture accounts for only 0.005 percent of the water at Earth’s surface. It is this small amount of water, however, that exerts the most direct influence on evaporation from soils. The biosphere, though primarily H2O in composition, contains very little of the total water at the terrestrial surface, only about 0.00004 percent, yet the biosphere plays a major role in the transport of water vapour back into the atmosphere by the process of transpiration.

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San Francisco International Airport has a “wag brigade”—a pack of therapy dogs available to calm nervous fliers. Joining the comfort canines is LiLou, a therapy pig.

As will be seen in the next section, Earth’s waters are not pure H2O but contain dissolved and particulate materials. Thus, the masses of water at Earth’s surface are major receptacles of inorganic and organic substances, and water movement plays a dominant role in the transportation of these substances about the planet’s surface.