The hydrosphere (from Greek ὕδωρ hydōr, "water"[1] and σφαῖρα sphaira, "sphere"[2]) is the combined mass of water found on, under, and above the surface of a planet, minor planet or natural satellite. Although the Earth's hydrosphere has been around for longer than 4 billion years, it continues to change in size. This is caused by seafloor spreading and continental drift, which rearranges the land and ocean.[3]

It has been estimated that there are 1,386 million cubic kilometres (333,000,000 cubic miles) of water on Earth.[4] This includes water in liquid and frozen forms in groundwater, oceans, lakes and streams. Saltwater accounts for 97.5% of this amount, whereas fresh water accounts for only 2.5%. Of this fresh water, 68.9% is in the form of ice and permanent snow cover in the Arctic, the Antarctic, and mountain glaciers; 30.8% is in the form of fresh groundwater; and only 0.3% of the fresh water on Earth is in easily accessible lakes, reservoirs and river systems.[4]

The total mass of the Earth's hydrosphere is about 1.4 × 1018 tonnes, which is about 0.023% of Earth's total mass. At any given time, about 20 × 1012 tonnes of this is in the form of water vapor in the Earth's atmosphere (for practical purposes, 1 cubic meter of water weighs one tonne). Approximately 71% of Earth's surface, an area of some 361 million square kilometers (139.5 million square miles), is covered by ocean. The average salinity of Earth's oceans is about 35 grams of salt per kilogram of sea water (3.5%).[5]

World water distribution

Water cycle


The water cycle refers to the transfer of water from one state or reservoir to another. Reservoirs include atmospheric moisture (snow, rain and clouds), streams, oceans, rivers, lakes, groundwater, subterranean aquifers, polar ice caps and saturated soil. Solar energy, in the form of heat and light (insolation), and gravity cause the transfer from one state to another over periods from hours to thousands of years. Most evaporation comes from the oceans and is returned to the earth as snow or rain.[6]:27 Sublimation refers to evaporation from snow and ice. Transpiration refers to the expiration of water through the minute pores or stomata of trees. Evapotranspiration is the term used by hydrologists in reference to the three processes together, transpiration, sublimation and evaporation.[6]

Marq de Villiers has described the hydrosphere as a closed system in which water exists. The hydrosphere is intricate, complex, interdependent, all-pervading and stable and "seems purpose-built for regulating life."[6]:26 De Villiers claimed that, "On earth, the total amount of water has almost certainly not changed since geological times: what we had then we still have. Water can be polluted, abused, and misused but it is neither created nor destroyed, it only migrates. There is no evidence that water vapor escapes into space."[6]:26

"Every year the turnover of water on Earth involves 577,000 km3 of water. This is water that evaporates from the oceanic surface (502,800 km3) and from land (74,200 km3). The same amount of water falls as atmospheric precipitation, 458,000 km3 on the ocean and 119,000 km3 on land. The difference between precipitation and evaporation from the land surface (119,000 - 74,200 = 44,800 km3/year) represents the total runoff of the Earth's rivers (42,700 km3/year) and direct groundwater runoff to the ocean (2100 km3/year). These are the principal sources of fresh water to support life necessities and man's economic activities."[4]

Water is a basic necessity of life. Since 2/3 of the Earth is covered by water, the Earth is also called the blue planet and the watery planet.[notes 1] Hydrosphere plays an important role in the existence of the atmosphere in its present form. Oceans are important in this regard. When the Earth was formed it had only a very thin atmosphere rich in hydrogen and helium similar to the present atmosphere of Mercury. Later the gases hydrogen and helium were expelled from the atmosphere. The gases and water vapor released as the Earth cooled became its present atmosphere. Other gases and water vapor released by volcanoes also entered the atmosphere. As the Earth cooled the water vapor in the atmosphere condensed and fell as rain. The atmosphere cooled further as atmospheric carbon dioxide dissolved in to rain water. In turn this further caused the water vapor to condense and fall as rain. This rain water filled the depressions on the Earth's surface and formed the oceans. It is estimated that this occurred about 4000 million years ago. The first life forms began in the oceans. These organisms did not breathe oxygen. Later, when cyanobacteria evolved, the process of conversion of carbon dioxide into food and oxygen began. As a result, Earth's atmosphere has a distinctly different composition from that of other planets and allowed for life to evolve on Earth.

Recharging reservoirs

According to Igor A. Shiklomanov, it takes 2500 years for the complete recharge and replenishment of oceanic waters, 10,000 years for permafrost and ice, 1500 years for deep groundwater and mountainous glaciers, 17 years in lakes and 16 days in rivers.[4]

Specific fresh water availability

"Specific water availability is the residual (after use) per capita quantity of fresh water."[4] Fresh water resources are unevenly distributed in terms of space and time and can go from floods to water shortages within months in the same area. In 1998 76% of the total population had a specific water availability of less than 5.0 thousand m³ per year per capita. Already by 1998, 35% of the global population suffered "very low or catastrophically low water supplies" and Shiklomanov predicted that the situation would deteriorate in the twenty-first century with "most of the Earth's population will be living under the conditions of low or catastrophically low water supply" by 2025. There is only 2.5% of fresh water in the hydrosphere and only 0.25% of water is accessible for our use.

See also


  1. ^ According to planetary geologist, Ronald Greeley, "Water is very common in the outer solar system." Europa holds more water than earth's oceans.


  1. ^ ὕδωρ, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
  2. ^ σφαῖρα, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
  3. ^ “Our Changing Planet: an Introduction to Earth System Science and Global Environmental Change.” Our Changing Planet: an Introduction to Earth System Science and Global Environmental Change, by Fred T. Mackenzie, 2nd ed., Pearson Education, 2011, pp. 88–91.
  4. ^ a b c d e World Water Resources: A New Appraisal and Assessment for the 21st Century (Report). UNESCO. 1998. Archived from the original on 27 September 2013. Retrieved 13 June 2013.
  5. ^ Kennish, Michael J. (2001). Practical handbook of marine science. Marine science series (3rd ed.). CRC Press. p. 35. ISBN 0-8493-2391-6.
  6. ^ a b c d Marq de Villiers (2003). Water: The Fate of Our Most Precious Resource (2 ed.). Toronto, Ontario: McClelland & Stewart. p. 453. ISBN 978-0-7710-2641-6. OCLC 43365804., revised 2003|Governor General's Award (1999)


External links

  1. ^ “Our Changing Planet: an Introduction to Earth System Science and Global Environmental Change.” Our Changing Planet: an Introduction to Earth System Science and Global Environmental Change, by Fred T. Mackenzie, 2nd ed., Pearson Education, 2011, pp. 88–91.
Biogeochemical cycle

In ecology and Earth science, a biogeochemical cycle or substance turnover or cycling of substances is a pathway by which a chemical substance moves through biotic (biosphere) and abiotic (lithosphere, atmosphere, and hydrosphere) compartments of Earth. There are biogeochemical cycles for the chemical elements calcium, carbon, hydrogen, mercury, nitrogen, oxygen, phosphorus, selenium, and sulfur; molecular cycles for water and silica; macroscopic cycles such as the rock cycle; as well as human-induced cycles for synthetic compounds such as polychlorinated biphenyl (PCB). In some cycles there are reservoirs where a substance remains for a long period of time (such as an ocean or lake for water).


Biogeochemistry is the scientific discipline that involves the study of the chemical, physical, geological, and biological processes and reactions that govern the composition of the natural environment (including the biosphere, the cryosphere, the hydrosphere, the pedosphere, the atmosphere, and the lithosphere). In particular, biogeochemistry is the study of the cycles of chemical elements, such as carbon and nitrogen, and their interactions with and incorporation into living things transported through earth scale biological systems in space through time. The field focuses on chemical cycles which are either driven by or influence biological activity. Particular emphasis is placed on the study of carbon, nitrogen, sulfur, and phosphorus cycles. Biogeochemistry is a systems science closely related to systems ecology.


The biosphere (from Greek βίος bíos "life" and σφαῖρα sphaira "sphere") also known as the ecosphere (from Greek οἶκος oîkos "environment" and σφαῖρα), is the worldwide sum of all ecosystems. It can also be termed the zone of life on Earth, a closed system (apart from solar and cosmic radiation and heat from the interior

of the Earth), and largely self-regulating. By the most general biophysiological definition, the biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements of the lithosphere, geosphere, hydrosphere, and atmosphere. The biosphere is postulated to have evolved, beginning with a process of biopoiesis (life created naturally from non-living matter, such as simple organic compounds) or biogenesis (life created from living matter), at least some 3.5 billion years ago.In a general sense, biospheres are any closed, self-regulating systems containing ecosystems. This includes artificial biospheres such as Biosphere 2 and BIOS-3, and potentially ones on other planets or moons.

Charlie Houchin

Charles "Charlie" Houchin (born November 3, 1987) is an American former competition swimmer who has had his greatest international success in freestyle relay events. He earned a gold medal as a member of the winning United States team in the 4×200-meter freestyle relay at the 2012 Summer Olympics. He is the CEO and founder of HydroXphere (pronounced "Hydrosphere"). Their product, Meet Central, is a mobile app that can operate an entire swim meet from iPhones.

Earth science

Earth science or geoscience includes all fields of natural science related to the planet Earth. This is a branch of science dealing with the physical constitution of the Earth and its atmosphere. Earth science is the study of our planet's physical characteristics, from earthquakes to raindrops, and floods to fossils. Earth science can be considered to be a branch of planetary science, but with a much older history. Earth science encompasses four main branches of study, the lithosphere, the hydrosphere, the atmosphere, and the biosphere, each of which is further broken down into more specialized fields.

There are both reductionist and holistic approaches to earth sciences. It is also the study of Earth and its neighbors in space. Some earth scientists use their knowledge of the planet to locate and develop energy and mineral resources. Others study the impact of human activity on Earth's environment, and design methods to protect the planet. Some use their knowledge about earth processes such as volcanoes, earthquakes, and hurricanes to plan communities that will not expose people to these dangerous events.

The earth sciences can include the study of geology, the lithosphere, and the large-scale structure of the earth's interior, as well as the atmosphere, hydrosphere, and biosphere. Typically, earth scientists use tools from geography, chronology, physics, chemistry, biology, and mathematics to build a quantitative understanding of how the earth works and evolves. Earth science affects our everyday lives. For example, meteorologists study the weather and watch for dangerous storms. Hydrologists study water and warn of floods. Seismologists study earthquakes and try to predict where they will strike. Geologists study rocks and help to locate useful minerals. Earth scientists often work in the field—perhaps climbing mountains, exploring the seabed, crawling through caves, or wading in swamps. They measure and collect samples (such as rocks or river water), then they record their findings on charts and maps.

Environmental geology

Environmental geology, like hydrogeology, is an applied science concerned with the practical application of the principles of geology in the solving of environmental problems. It is a multidisciplinary field that is closely related to engineering geology and, to a lesser extent, to environmental geography. Each of these fields involves the study of the interaction of humans with the geologic environment, including the biosphere, the lithosphere, the hydrosphere, and to some extent the atmosphere. In other words, environmental geology is the application of geological information to solve conflicts, minimizing possible adverse environmental degradation or maximizing possible advantageous condition resulting from the use of natural and modified environment.

Environmental geology includes:

managing geological and hydrogeological resources such as fossil fuels, minerals, water (surface and ground water), and land use.

studying the earth's surface through the disciplines of geomorphology, and edaphology;

defining and mitigating exposure of natural hazards on humans

managing industrial and domestic waste disposal and minimizing or eliminating effects of pollution, and

performing associated activities, often involving litigation.A peer-reviewed journal in the field is Environmental Earth Sciences (ISSN 1866-6280), formerly Environmental Geology (ISSN 0943-0105).

Environmental soil science

Environmental soil science is the study of the interaction of humans with the pedosphere as well as critical aspects of the biosphere, the lithosphere, the hydrosphere, and the atmosphere. Environmental soil science addresses both the fundamental and applied aspects of the field including: buffers and surface water quality, vadose zone functions, septic drain field site assessment and function, land treatment of wastewater, stormwater, erosion control, soil contamination with metals and pesticides, remediation of contaminated soils, restoration of wetlands, soil degradation, nutrient management, movement of viruses and bacteria in soils and waters, bioremediation, application of molecular biology and genetic engineering to development of soil microbes that can degrade hazardous pollutants, land use, global warming, acid rain, and the study of anthropogenic soils, such as terra preta. Much of the research done in environmental soil science is produced through the use of models.


Geography (from Greek: γεωγραφία, geographia, literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and planets. The first person to use the word γεωγραφία was Eratosthenes (276–194 BC). Geography is an all-encompassing discipline that seeks an understanding of Earth and its human and natural complexities—not merely where objects are, but also how they have changed and come to be.

Geography is often defined in terms of two branches: human geography and physical geography. Human geography deals with the study of people and their communities, cultures, economies, and interactions with the environment by studying their relations with and across space and place. Physical geography deals with the study of processes and patterns in the natural environment like the atmosphere, hydrosphere, biosphere, and geosphere.

The four historical traditions in geographical research are: spatial analyses of natural and the human phenomena, area studies of places and regions, studies of human-land relationships, and the Earth sciences. Geography has been called "the world discipline" and "the bridge between the human and the physical sciences".


There are several conflicting definitions for geosphere.

The geosphere may be taken as the collective name for the lithosphere, the hydrosphere, the cryosphere, and the atmosphere. The different collectives of the geosphere are able to exchange different mass and/or energy fluxes. Fluxes being the measurable amount of change. The exchange of these fluxes affects the balance of the different spheres of the geosphere. An example is how the soil acts as a part of the biosphere. While also acting as a source of flux exchange.

In Aristotelian physics, the term was applied to four spherical natural places, concentrically nested around the center of the Earth, as described in the lectures Physica and Meteorologica. They were believed to explain the motions of the four terrestrial elements: Earth, Water, Air and Fire.

In modern texts and in Earth system science, geosphere refers to the solid parts of the Earth; it is used along with atmosphere, hydrosphere, and biosphere to describe the systems of the Earth (the interaction of these systems with the magnetosphere is sometimes listed). In that context, sometimes the term lithosphere is used instead of geosphere or solid Earth. The lithosphere, however, only refers to the uppermost layers of the solid Earth (oceanic and continental crustal rocks and uppermost mantle).Since space exploration began, it has been observed that the extent of the ionosphere or plasmasphere is highly variable, and often much larger than previously appreciated, at times extending to the boundaries of the Earth's magnetosphere or geomagnetosphere. This highly variable outer boundary of geogenic matter has been referred to as the "geopause", to suggest the relative scarcity of such matter beyond it, where the solar wind dominates.

Marine regression

Marine regression is a geological process occurring when areas of submerged seafloor are exposed above the sea level. The opposite event, marine transgression, occurs when flooding from the sea covers previously exposed land.Evidence of marine regressions and transgressions occurs throughout the fossil record, and these fluctuations are thought to have caused or contributed to several mass extinctions, among them the Permian-Triassic extinction event (250 million years ago) and Cretaceous–Paleogene extinction event (66 Ma). At the time of the Permian-Triassic extinction, the largest extinction event in the Earth's history, global sea level fell 250 m (820 ft).A major regression could itself cause marine organisms in shallow seas to go extinct, but mass extinctions tend to involve both terrestrial and aquatic species, and it is harder to see how a marine regression could cause widespread extinctions of land animals. Regressions are, therefore, seen as correlates or symptoms of major extinctions, rather than primary causes. The Permian regression might have been related to the formation of Pangaea: the accumulation of all the major landmasses into one body could have facilitated a regression, by providing "a slight enlargement of the ocean basins as the great continents coalesced." However, that cause could not have applied in all, or even many, other cases.

During the ice ages of the Pleistocene, a clear correlation existed between marine regressions and episodes of glaciation; as the balance shifts between the global cryosphere and hydrosphere, more of the planet's water in ice sheets means less in the oceans. At the height of the last ice age, at around 18,000 years before the present, the global sea level was 120 to 130 m (390-425 ft) lower than today. A cold spell around 6 million years ago was linked to an advance in glaciation, a marine regression, and the start of the Messinian salinity crisis in the Mediterranean basin. Some major regressions of the past, however, seem unrelated to glaciation episodes — the regression that accompanied the mass extinction at the end of the Cretaceous Period being one example.

A clear and certain understanding of major marine regressions has not yet been achieved; according to one hypothesis, regressions may be linked to a "slowdown in sea-floor spreading, leading to a generalized drop in sea level (as the mid-ocean ridges would take up less space)...." In that view, major marine regressions are one aspect of a normal variation in rates of plate tectonic activity, which lead to major episodes of global volcanism like the Siberian Traps and the Deccan Traps, which in turn cause large extinction events.

Microscale meteorology

Microscale meteorology is the study of short-lived atmospheric phenomena smaller than mesoscale, about 1 km or less. These two branches of meteorology are sometimes grouped together as "mesoscale and microscale meteorology" (MMM) and together study all phenomena smaller than synoptic scale; that is they study features generally too small to be depicted on a weather map. These include small and generally fleeting cloud "puffs" and other small cloud features.

Microscale meteorology controls the most important mixing and dilution processes in the atmosphere. Important topics in microscale meteorology include heat transfer and gas exchange between soil, vegetation, and/or surface water and the atmosphere caused by near-ground turbulence. Measuring these transport processes involves use of micrometeorological (or flux) towers. Variables often measured or derived include net radiation, sensible heat flux, latent heat flux, ground heat storage, and fluxes of trace gases important to the atmosphere, biosphere, and hydrosphere.


An ocean (from Ancient Greek Ὠκεανός, transc. Okeanós) is a body of water that composes much of a planet's hydrosphere. On Earth, an ocean is one of the major conventional divisions of the World Ocean. These are, in descending order by area, the Pacific, Atlantic, Indian, Southern (Antarctic), and Arctic Oceans. The word "ocean" is often used interchangeably with "sea" in American English. Strictly speaking, a sea is a body of water (generally a division of the world ocean) partly or fully enclosed by land, though "the sea" refers also to the oceans.

Saline water covers approximately 361,000,000 km2 (139,000,000 sq mi) and is customarily divided into several principal oceans and smaller seas, with the ocean covering approximately 71% of Earth's surface and 90% of the Earth's biosphere. The ocean contains 97% of Earth's water, and oceanographers have stated that less than 5% of the World Ocean has been explored. The total volume is approximately 1.35 billion cubic kilometers (320 million cu mi) with an average depth of nearly 3,700 meters (12,100 ft).As the world ocean is the principal component of Earth's hydrosphere, it is integral to life, forms part of the carbon cycle, and influences climate and weather patterns. The World Ocean is the habitat of 230,000 known species, but because much of it is unexplored, the number of species that exist in the ocean is much larger, possibly over two million. The origin of Earth's oceans is unknown; oceans are thought to have formed in the Hadean eon and may have been the impetus for the emergence of life.

Extraterrestrial oceans may be composed of water or other elements and compounds. The only confirmed large stable bodies of extraterrestrial surface liquids are the lakes of Titan, although there is evidence for the existence of oceans elsewhere in the Solar System. Early in their geologic histories, Mars and Venus are theorized to have had large water oceans. The Mars ocean hypothesis suggests that nearly a third of the surface of Mars was once covered by water, and a runaway greenhouse effect may have boiled away the global ocean of Venus. Compounds such as salts and ammonia dissolved in water lower its freezing point so that water might exist in large quantities in extraterrestrial environments as brine or convecting ice. Unconfirmed oceans are speculated beneath the surface of many dwarf planets and natural satellites; notably, the ocean of the moon Europa is estimated to have over twice the water volume of Earth. The Solar System's giant planets are also thought to have liquid atmospheric layers of yet to be confirmed compositions. Oceans may also exist on exoplanets and exomoons, including surface oceans of liquid water within a circumstellar habitable zone. Ocean planets are a hypothetical type of planet with a surface completely covered with liquid.

Orhei District

Orhei is a district (Romanian: raion) in central Moldova, with its administrative center in the city of Orhei. As of 2014 Moldovan Census its population was 101,502.

Outline of Earth

The following outline is provided as an overview of and topical guide to the planet Earth:

Earth – third planet from the Sun, the densest planet in the Solar System, the largest of the Solar System's four terrestrial planets, and the only astronomical object known to harbor life.

Oxygen cycle

The oxygen cycle is the biogeochemical transitions of oxygen atoms between different oxidation states in ions, oxides, and molecules through redox reactions within and between the spheres/reservoirs of the planet Earth. The word oxygen in the literature typically refers to the most common oxygen allotrope, elemental/diatomic oxygen (O2), as it is a common product or reactant of many biogeochemical redox reactions within the cycle. Processes within the oxygen cycle are considered to be biological or geological and are evaluated as either a source (O2 production) or sink (O2 consumption).


The pedosphere (from Greek πέδον pedon "soil" or "earth" and σφαῖρα sphaira "sphere") is the outermost layer of the Earth that is composed of soil and subject to soil formation processes. It exists at the interface of the lithosphere, atmosphere, hydrosphere and biosphere. The pedosphere is the skin of the Earth and only develops when there is a dynamic interaction between the atmosphere (air in and above the soil), biosphere (living organisms), lithosphere (unconsolidated regolith and consolidated bedrock) and the hydrosphere (water in, on and below the soil). The pedosphere is the foundation of terrestrial life on Earth.

The pedosphere acts as the mediator of chemical and biogeochemical flux into and out of these respective systems and is made up of gaseous, mineralic, fluid and biologic components. The pedosphere lies within the Critical Zone, a broader interface that includes vegetation, pedosphere, groundwater aquifer systems, regolith and finally ends at some depth in the bedrock where the biosphere and hydrosphere cease to make significant changes to the chemistry at depth. As part of the larger global system, any particular environment in which soil forms is influenced solely by its geographic position on the globe as climatic, geologic, biologic and anthropogenic changes occur with changes in longitude and latitude.

The pedosphere lies below the vegetative cover of the biosphere and above the hydrosphere and lithosphere. The soil forming process (pedogenesis) can begin without the aid of biology but is significantly quickened in the presence of biologic reactions. Soil formation begins with the chemical and/or physical breakdown of minerals to form the initial material that overlies the bedrock substrate. Biology quickens this by secreting acidic compounds (dominantly fulvic acids) that help break rock apart. Particular biologic pioneers are lichen, mosses and seed bearing plants, but many other inorganic reactions take place that diversify the chemical makeup of the early soil layer. Once weathering and decomposition products accumulate, a coherent soil body allows the migration of fluids both vertically and laterally through the soil profile, causing ion exchange between solid, fluid and gaseous phases. As time progresses, the bulk geochemistry of the soil layer will deviate away from the initial composition of the bedrock and will evolve to a chemistry that reflects the type of reactions that take place in the soil.

Solid earth

Solid earth refers to "the earth beneath our feet" or terra firma, the planet's solid surface and its interior. It contrasts with the Earth's fluid envelopes, the atmosphere and hydrosphere (but includes the ocean basin), as well as the biosphere and interactions with the Sun. It includes the liquid core.Solid-earth science refers to the corresponding methods of study, a subset of Earth sciences, predominantly geophysics and geology, excluding aeronomy, atmospheric sciences, oceanography, hydrology, and ecology.

Spring (hydrology)

A spring is a point at which water flows from an aquifer to the Earth's surface. It is a component of the hydrosphere.

World Ocean

The World Ocean or Global Ocean (colloquially the sea or the ocean) is the interconnected system of Earth's oceanic waters, and comprises the bulk of the hydrosphere, covering 361,132,000 square kilometres (139,434,000 sq mi) (70.8%) of Earth's surface, with a total volume of roughly 1,332,000,000 cubic kilometres (320,000,000 cu mi).

On Earth

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