With 71% of our home planet being covered by water, it is undeniable why the Earth is called the Blue Planet. Whether it is for the liquid state of water found in the lakes, rivers, streams, oceans, underground or even the other states like the atmospheric gaseous water vapor or the solid ice state (in mountains), any form of water in our planet falls under Hydrosphere.
Given that, the overall reserves of water in Earth can approximately fit in the voluminous figures of 1386 ml.km3. In specific parts of hydrosphere, reserves might vary from one to other. A substantial portion of water sources of app. 97% comprises of sea water while the remaining 3% comprises of Fresh water. That said, almost 69% of the fresh water is in ice form and resembles the permanent snow covering Antarctic, Artic as well as the glaciers of mountains. The remaining 31% is in fresh ground water form where only a bare-minimum of 0.3% of the fresh water sources can be accessible conveniently. The overall weight of the hydrosphere of our mother earth is 1.4 × 1018 tons. That again, precisely implies the gigantic and unimaginable volume of water we are surrounded by all the time!
The Hydrological Cycle or simply called the water cycle elucidates the water circulation within the hydrosphere of earth. This denotes the modifications in the water’s physical state between the land, atmosphere, surface as well as the subsurface waters. Along with the storage in myriad compartments wherein the rivers resemble one such compartment, the multitudinous cycles which encompasses the water cycle of earth can be given under as:
- Precipitation: It forms the moisture in atmosphere that erstwhile had condensed forming the clouds (the transformation involved is solid/gaseous phases from liquid phases). The precipitation occurs as snowfall, rainfall, fog, hail and others.
- Evaporation: It describes the water-transfer from surface of water bodies into atmosphere. This triggers a transformation in the water’s physical sate from a state of liquid to a gaseous state. Furthermore, Evaporation might as well be contributed from transpiration and to a lesser degree also from perspiration generated from mammals. This kind of transfer can be given under as Evapotranspiration. There is almost 90% of the overall atmospheric water from the process of evaporation, however, the rest 10% from transpiration.
- Runoff: It involves the myriad ways by which the water from land surface stoops down the slope into the oceans. The flow of water in rivers and streams can be delayed for some time in lakes. Not entirely, all the water precipitated comes back to the sea as runoff rather, a significant amount of it becomes evaporated prior to reaching the aquifer or even the ocean.
- Infiltration: It resembles the change to ground water from surface water. The rate of infiltration is dependent on the permeability of rock or soil along with other factors. The water infiltrated might reach another compartment called the aquifer or groundwater. This might move steadily and slowly such that the water is able to return as surface water post storage within the aquifer for a time period. The water can come back to the surface of land at lower elevation with infiltration by a gravitational force or pressures induced by the gravity.
- Subsurface Flow: It resembles the water movement within earth. Post infiltrating, the water of subsurface might come back to the surface or steadily penetrate into the ocean.
Since millions of years, the history of the hydrosphere formation and its sustenance is a fact retrieved from the theory of the Hydrologic Cycle which is a part of Physics. However, the origin of Hydrosphere and its original Physical state is still a mystery that remains.