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Spheres of the Earth

There are four main spheres of the earth.

  • Atmosphere
  • Hydrosphere
  • Lithosphere
  • Biosphere

(1). Atmosphere:

The uppermost gaseous layer of the earth is called the Earth’s Atmosphere. The earth’s atmosphere stretches from the earth surface to thousands of kilometer up. The thickness of the atmosphere is about 10,000 km. After the height of 10,000 km, the space starts. The earth’s atmosphere is not only the air we breathe, but it is much more than the ordinary inhale-able air. It consists of many gases, including the major gases like Oxygen, Hydrogen, Nitrogen, Helium, Carbon Dioxide etc. The gases with high specific gravity are closer to the earth surface, while those which are lighter are present in the high altitude. For, example, Hydrogen is lighter than Oxygen. Therefore, Hydrogen gas is present in upper atmosphere, while Oxygen is present near to the surface of the earth. The percentage of different gases in the atmosphere is different. For example, the percentage of Nitrogen in the atmosphere is 78%, Oxygen 21%, Carbon-dioxide 0.04%, Hydrogen0.000055%, and Helium gas is 0.0005%.

Layering of Atmosphere:

The atmosphere of the Earth is sub-divided into five layers, based on temperature.

  1. The Troposphere: The layer closest to the earth surface is known as Troposphere. It is starts from the earth surface and ends at 7 to 15 kilometers. It is the site of all weathers. The variation of weather from region to region occurs in this layer. The troposphere is bounded from the top by a layer known as Tropopause. The tropopause separates the troposphere from another other layer namely “Stratosphere”. Troposphere is denser than the rest of the spheres. The majority of the mass of the atmosphere is contained by the troposphere. It contains about 80% mass of the atmosphere. Most of the water vapors and dust particles are also contained by this layer of the atmosphere. Clouds also float through troposphere. Temperature in this sphere decreases with the altitude.
  2. The Stratosphere: The stratosphere is separated from troposphere by means of a thin layer called “Tropopause”. The stratosphere starts from above the troposphere and ends at an altitude of 50 kilometers. Temperature in the atmosphere increases with altitude in this sphere. This layer of the atmosphere is enriched with Ozone. Ozone the state of Oxygen which consists of the composition of three oxygen molecules. Ozone layer protects the earth lower atmosphere from harmful radiations present in the Sun light. It prohibits the ultraviolet radiation to pass through the stratosphere. The presence of ultraviolet rays in this layer is responsible for temperature increase in the stratosphere.
  3. The Mesosphere: At the top of the stratosphere, there is another layer called Mesosphere, which stretches from 50 kilometers to 85 km. The temperature decreases in the mesosphere with altitude. The top boundary of the mesosphere is called “mesopause”. The density of the mesosphere is lower than the low lying two spheres, namely troposphere and the stratosphere.
  4. The Thermosphere: This sphere is very hot that is why it is known as the Thermosphere. The thermosphere is located above the mesopause and reaches out to around 600 kilometers (372 miles). Not much is known about the thermosphere except that temperatures increase with altitude. Solar radiation makes the upper regions of the thermosphere very hot, reaching temperatures as high as 2,000°C (3,600°F).
  5. The Exsosphere: The uppermost layer of the atmosphere is known as the Exosphere. At this level the atmosphere blends with the outer space. The gravitational pulls so small that the molecules of the atmosphere escape the gravity and enter into the outer space.

(2). Hydrosphere:

Hydrosphere is the spherical part of the earth, which is completely composed of water. The oceans, seas, rivers, lakes, ponds, streams, icebergs/glaciers underground aquifers, clouds, water vapors, and other water-bodies are included in the hydrosphere. Hydrosphere is the total amount of water present on and within the planet. The water of the planet comes in three forms, the liquid, the vapors and the solid. The liquid water is found on the earth surface and underground in the form of rivers, oceans, lakes, underground aquifers, streams, wells, and ponds. The solid water is found in the form of ice and glaciers. The regions with very low temperature are enriched with solid-state water. The gaseous/vapor water is found in the atmosphere in the form of clouds, fog, and other water vapors. About 71 percent of earth surface is covered with water. The hydrosphere is subdivided into three categories.

  1. Liquid Hydrosphere: On Earth, liquid water exists on the surface in the form of oceans, lakes and rivers. It also exists below ground—as groundwater, in wells and aquifers.
  2. Vaporous Hydrosphere: Water found in atmosphere in the form of vapors and steam is known as the Vaporous Hydrosphere. Fog and Clouds are the examples of the Vaporous Hyrdrosphere.
  3. Cryosphere: The cryosphere is the frozen part the total water of the planet. This sphere includes water in the form of ice, glaciers and snow. Cryosphere contains water of extremely low temperature.

Water Cycle: Water moves through the hydrosphere in a cycle. Water evaporates from the surface water-bodies into the clouds, then falls to Earth in the form of rain or snow. The liquid water collects in rivers, lakes and oceans, while the solid water of the cryosphere is heated in the sunlight, melts and starts flowing through the rivers and streams, ultimately reaches to the seas and oceans. Then it evaporates into the atmosphere to start the cycle all over again. This is called the water cycle.

(3). Lithosphere:

Lithosphere is the upper most sold hard layer of the earth. Lithosphere consists of the earth’s crust and the upper mantle. The upper mantle and the earth’s crust, both are hard solid part of the earth. From here, the molten layers of the earth starts that are known as the molten mantle, and the liquid outer Core. Lithosphere is divided into the plate tectonics. The plates tectonic are the cracked shell of the earth crust and the upper mantle. These plate either submerge, or diverge or move transversely due to the convection in the lower mantle. Read detail of the Lithospheric layer of the earth.

(4). Biosphere:

The global ecosystem consists of living organisms and non-living organisms, which influence the living thing directly or indirectly. The biosphere is classified into two categories, the biota, and the abiota. Biota means living things, where abiota consists of those factors which influence the living things. In other words, the global ecosystem is known as the biosphere of the Earth.

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