Lithosphere, Hydrosphere & Atmosphere

  • The earth comprises three spheres— Lithosphere, Hydrosphere and Atmosphere. These spheres are generally considered as land (soil), water and air respectively.
  • The study of lithosphere, hydrosphere and atmosphere is known as 'Geomorphology', Oceanography and Climatology respectively.
  • There are three spheres of the earth namely, Lithosphere, Hydrosphere and Atmosphere. The study of Lithosphere, Hydrosphere and Atmosphere is known as 'Geomorphology', 'Oceanography' and 'Climatology' respectively.
    (Note: The study of Biosphere, the common life-existing portion of lithosphere, hydrosphere & atmosphere, is known as 'Ecology'.)

Lithosphere

  • The term' Lithosphere' is the combination of two Greek words Lithos (= rocky, solid) and Sphaira (= sphere). Thus, the meaning of Lithosphere is solid layers of rock material on the earth's surface, both on the continents and ocean floors.
  • Earth's lithosphere constitutes the hard and rigid outer vertical layer of the earth.
  • The lithosphere is subdivided horizontally into tectonic plates.
  • The lithosphere (or land) covers approx. 29% (exactly, 29.22%) of total area of the earth.
  • The lithosphere is comprised of the crust and the uppermost mantle.

Structure of Earth's Interior

  • The Earth's interior is made up of three layers, namely crust (Sial), Mantle (Sima) and Core (Nife). The crustal layer extends between 30 km to 100 km deep.

Crust (Sial):

The crust is thicker in the continents than on the ocean floors. The crustal layer is of lighter density compared to the interior layers. As the crustal layer comprises of rocks rich in Silica and Aluminium, it is called Sial =Silica +Aluminium) layer.

Mantle (Sima):

Below the sial layer lies the mantle layer which extends up to a depth of 2900 km. As the mantle comprises of materials rich in Silica and Magnesium, it is called Sima (=silica +Magnesium) layer.

Core (Nife):

The core of the earth consists of metals in liquid or plastic state of high temperature and pressure. The core of the earth has a radius of 3400 km. As Nickel and Ferrum (Latin name of Iron) are dominant in the core, it is called Nife (=Nickel +Ferrum) layer. This accounts for Earth's magnetism.

 

Hydrosphere

  • The term Hydrosphere is the combination of two Greek words Hydro (= water, liquid) and Sphaira (= sphere). Thus, the meaning of Hydrosphere is the layer of water on the surface of the earth in the form of oceans, lakes, rivers and other waterbodies.
  • Hydrosphere (or water) covers approx. 71% (exactly 70.78%) of the total surface area of the earth. Therefore, the earth is sometimes called a watery planet. It is also known as Blue Planet because the earth appears blue due to water from the space.
  • Continents may be considered as large islands rising from the vast oceans.
  • Water occurs on the land in the form of ice-sheets in polar region and in the form of glaciers on high mountains. Water occurs in the water in the form of liquid water or ice-floes in the oceans and seas. Water also occurs below the surface of the land in the form of underground water. Water also occurs above the surface of land in the form of water-vapour in the lower layers of the atmosphere.
    Even flora (plants) and fauna (animals), including man are predominantly made up of water. This means water is base of lives of flora and fauna. That's why, it is saying 'Water is life' or 'If there is water there is life' or, 'As long as there is water there is life' and so on.
  • Out of the total volume of water available, 97% lie in the vast oceans but it is saline water (in the words of English poet S. T. Coleridge,'water, water everywhere and not a drop to drink). 2% is stored in the form of ice-sheets and less than 1% is available as fresh water i.e. nonsaline/nonsalty water.
  • The earth has an abundance of water, but unfortunately, only a small percentage (about 0.3%), is even usable by humans (men). The other 99.7% lies in the oceans, ice-sheets, fresh waterbodies, soils (surface water and underground water), and floating in the atmosphere. Still, much of the 0.3% water that is usable is unattainable. Most of the water used by humans comes from the rivers. The visible bodies of water are referred as surface water. The majority of water is actually found underground as soil moisture and in aquifiers. Ground water can feed the streams, that's why a river can keep flowing even when there has been no percipitation. Human can use both surface and ground water. Drinkable water is called Potable water.

Water-Cycle

  • The circulation of water among hydrosphere, atmosphere and lithosphere is called water-cycle or hydrological-cycle.
  • Differential heating by the Sun is responsible for the circulation of water in the hydrosphere, similar to the circulation of air in atmosphere.

  • When the surface water in the oceans, seas, rivers, lakes etc. gets heated by the Sun's rays, evaporation takes place and water-vapour is added on to the lower layers of the atmosphere. As we know that water-vapour in the atmosphere may get cooled leading to condensation of water into tiny droplets which form clouds. Such clouds may cause precipitation of water in the form of rainfall or snowfall on the surface. Rainfall on the land leads to surface run-off in the form of rivers which reach the oceans ultimately.
  • In this process of circulation, water is consumed by plants and animals, in the biosphere. Water may get temporarily stored on the land in the form of ice-sheets, lakes, ponds or as underground water below the land surface.

 

Atmosphere

  • The term Atmosphere is combination of two Greek words, Atmos (= vapour) and Sphaira (= sphere). Thus, the meaning of atmosphere is gaseous envelop that surrounds the earth.
  • Among the three major elements of environment, the atmosphere is the most dynamic as changes take place in it not only from one season to another, but also over shorter periods of a few hours.
  • Out of the total mass of the atmosphere, 99% found in a height of 32 km from the earth's surface. It is to be noted that most of the atmospheric changes occur within this layer.
  • The atmosphere is held to the earth by the force of gravity.
  • The study of lower layers and upper layers of atmosphere is known as 'Meteorology' and' Aeorology' respectively.

Composition of Atmosphere

  • The atmosphere consists of a mixture of gases having a relatively uniform composition in the lower layers. An average sample of pure dry air consists of Nitrogen (78%), Oxygen (21%) and Argon (0.9%); other gases such as Carbon dioxide (0.03%), Hydrogen (0.01%), Helium (0.0005%) and Ozone (0.000001%) are present in minute quantities.
  • The lower layers of the atmosphere also contains water-vapour in variable quantities. Water-vapour is added to the atmosphere by evaporation from oceans, seas, lakes, rivers, ponds and other waterbodies. Though water-vapour may not exceed 3% to 4% of the total volume of air at any given place, but it plays an important role in the atmospheric process.
  • Apart from these gases, solid particles like dust, carbon, salt, pollen grains etc. are also found in the lower layers of the atmosphere.

Structure of Atmosphere

  • The density of the atmosphere decreases with height.
  • There are five layers of atmosphere: Troposphere, Stratosphere, Mesosphere, Thermosphere and Exosphere.
    Note: A simple formula to remember layers of atmosphere-.

1. Troposphere:

[Tropos (= rotating, changing) + Sphaira (= sphere) = Troposphere]- The lowest layer of atmosphere is called the Troposphere - In this layer, the temperature of air decreases with height at an average of 1° C for 165 metres. The troposphere extends up to a height of 8 km along the poles and 18 km along the equator. The upper limit of the troposphere is called tropopause. Most of the weather phenomena take place in this layer. Due to rotational turbulence that mixes the layers of air and weather phenomena occur, this sphere is known as Troposphere.

2. Stratosphere:

[Strato (= layer) + Sphaira (= sphere) — Stratosphere]- Above the troposphere is another layer called the stratosphere- The stratosphere extends up to a height of 50 km above the sea-level.
[
Sea Level: Level Sea level is the average level of the sea. It is the base level for measuring elevation (height) and depth on Earth.] In this layer, the temperature remains constant initally and then increases with height. As the stratosphere is free from clouds associated wether phenomena, conditions are ideal for flying of jet aircraft. The ozone in this layer absorbs harmful Ultra Violet (UV) radiation from the Sun.

3. Mesosphere:

[Meso (- Midde) + Sphaira (=Sphere) = Mesosphere]- Since mesosphere is a middle (meso = middle)sphere between stratosphere and thermosphere therefore it is called the Mesosphere - This sphere lies above the stratosphere and below the thermosphere. The mesosphere extends up to a height of 80 km.

4. Thermosphere:

[Thermos (- Heat) + Sphaira (= Sphere) = Thermosphere]. The fourth layer is called the Thermosphere - The thermosphere extends up to a height of about 513 km (according to National Aeronautics and Space Administration—NASA). Its lower part is called the Ionosphere. In the ionosphere layer, the temperature rises dramatically, reaching up to approx. 2500°C. This increase in temperature is due to the fact that gas molecules present in this layer absorb the Ultra-Violet and X-rays of the Sun. This results in the break up of the gas molecules into electrically charged particles called ions. These particles received the radio waves that is transmitted from the earth's surface and then reflect the radio waves back to the earth's surface. In this way, these particles make possible wireless and long distance communication. (Long radio waves— from D-layer of ionosphere, short radio waves—from E1, E2& F1,F2 layers of ionosphere).

5. Exosphere:

[Exo (= beyond) + Sphaira (= Sphere) = Exosphere]- It is outermost layer of atmosphere. The layer above the thermosphere is called the Exosphere. Since this sphere is beyond (exo = beyond) the thermosphere therefore it is called Exosphere. There is no distinct limit to the exosphere and this gives way in the enter-planetary space. The estimation of scientists is that Exosphere extends up to a height of 10,000 km.

  • The atmosphere is an important element of the environment. The layer of air act as a blanket or cover protecting the earth from Ultra Violet (UV) radiation and extremes of temperature.
  • The differential heating of the atmosphere by the Sun's rays produces circulation of air leading to winds, clouds and percipitation. The variation in climatic conditions on the earth is responsible for diversity in the distribution of plant and animal life.

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