The atmosphere is that the lower layer surrounding the world, with a mean composition, by volume of 78% nitrogen, 21% oxygen, 0.934% argon, 0.03% CO2, and traces of rare gases. This surprisingly uniform composition is achieved by convection within the troposphere and by diffusion above it, especially above 100 km, where diffusion is rapid within the thin atmosphere, and stirring is weak. Also present are atmospheric moisture, ammonia, ozone, and salts and solid particles. The atmosphere is usually divided into the troposphere, the stratosphere, the mesosphere, the ionosphere, and the thermosphere.
Disunion of Atmosphere
The modern atmosphere may be a gaseous mixture of ancient origin (Precambrian Period). The principal substance of this atmosphere is air, the medium of life also a serious industrial and chemical staple. Air may be a simple additive mixture of gases that's naturally odourless, colourless, tasteless, and formless, blended so thoroughly that it behaves as if were one gas. On the idea of the composition of gases, the atmosphere could also be divided into:
(i) Heterosphere: The term heterosphere indicates that the gases during this part of the atmosphere aren't evenly mixed, a condition quite different from the blended gases that we breathe closer to Earth within the atmosphere. Gases within the heterosphere are distributed in distinct layers, sorted by gravity, with the lightest elements (hydrogen and helium) at the margin of space, and heavier elements (oxygen, nitrogen) towards the world. The heterosphere begins at around 80 km altitude and extends outward some 10,000 km. However, for practical purposes, most meteorologists consider the highest of the atmosphere at around 480 km, an equivalent altitude we use for measuring the rate. Above 480 km, the atmosphere is rarified (nearly a vacuum) and is named the exosphere, which suggests the ‘outer sphere’. The exosphere contains individual atoms of the sunshine gases, viz. hydrogen and helium, weakly bonded by gravity.
2.Homosphere: Below the heterosphere is that the second compositional region of the atmosphere, which extends from the sea level up to an altitude of 80 km. albeit the atmosphere rapidly decreases in density with increasing altitude, the blend of gases is almost uniform throughout the homosphere. the sole exceptions are the concentration of ozone (O3) within the ozonosphere from 19–50 km, and therefore the variations in water vapour and pollutants within the lowest portion of the atmosphere near the Earth’s surface.
The stable mixture of gases throughout the homosphere has evolved slowly. this proportion of gases within the homosphere was attained approximately 600 million years ago.
Structure of the Atmosphere
For the aim of systematic study, on the idea of temperature and lapse rate, the atmosphere could also be classified under the subsequent layers:
(i) Troposphere, (ii) Stratosphere, (iii) Mesosphere, (iv) Exosphere
1. Troposphere: rock bottom layer of the atmosphere is understood as the troposphere. it's the house of the biospheric layer that supports life on Earth. Approximately 90% of the entire mass of the atmosphere and therefore the bulk of all water vapour, clouds, weather, and pollution are contained within the troposphere. The tropopause is that the upper limit which is defined by a mean temperature of –57°C, but its exact elevation varies with the season, latitude, surface temperatures and pressure. Near the equator, due to intense heating from below, the tropopause (upper limit of the troposphere) occurs at 18 km; within the middle latitudes, it occurs at 13 km and at the North and South Poles it's only 8 km or less above Earth’s surface. within the troposphere, temperatures decrease with increasing altitude at a mean rate of 6.4°C per km which is understood because of the normal lapse rate. In terms of temperature, the upper limit of the troposphere is –57°C.
2. Stratosphere and Ozonosphere: A layer of the Earth’s atmosphere, above the troposphere, extends from about 20 to 50 km above the ocean level. Temperature increases throughout the layer of the stratosphere. the warmth source is that the other functional layer called the ozonosphere or ozonosphere. Ozone may be a highly reactive oxygen molecule made from three oxygen atoms (O3) rather than the standard two (O2) that structure most of the oxygen gas. The ozonosphere is additionally referred to as the lower functional layer. Ozone absorbs the wavelength of ultraviolet and subsequently eradicates that energy at longer wavelengths as infrared (heat) energy. Through this process, most harmful ultraviolet is effectively ‘filtered’ from the incoming radiation, safeguarding life at Earth’s surface and heating the stratosphere.
3. Mesosphere: The mesosphere is that the area from 50 up to 80 km. Its upper boundary, the mesopause, is that the coldest portion of the atmosphere, averaging –90°C and has very low. It's characterised by continent-sized windstorms within the mesosphere. The very rarefied air is occupation vast waves at speed of more than 320 kmph. The upper boundary of this layer is named the mesopause.
4. Thermosphere (Heat Sphere): This sphere extends from 80 to 480 km in altitude. In the thermosphere, temperatures increase with height. High temperatures are generated within the thermosphere because the gas molecules absorb shortwave radiation.
However, the density of the molecules is so low that tiny actual heat is produced (heat is that the quantity of thermal energy). Moreover, the atmospheric pressure is extremely low. Heating within the lower atmosphere near Earth’s surface is different because the greater number of molecules within the denser atmosphere transmit their K.E. as sensible heat, meaning which will sense it.
Ionosphere: Ionosphere is that the lower part of the thermosphere. The atmosphere has two functional layers, so-called because both functions to filter harmful wavelengths of radiation, protecting Earth’s surface from bombardment in any significant quantity. The upper functional layer, the Ionosphere lies above 50 km which coincides with the thermosphere. It's composed of atoms that acquired electrical charges once they absorbed cosmic rays, gamma rays, X-rays, and shorter wavelengths of ultraviolet. These charged atoms are called ions, giving the ionosphere its name. Radiation bombards the ionosphere constantly, producing a continuing flux (flow) of electrons and charged atoms.
The four spheres of earth
Earth’s surface is where four open systems interface and interact. It's going to be seen that the three abiotic (non-living) systems are overlapping to make the realm of the abiotic (living) system. The abiotic spheres are the atmosphere, hydrosphere, and lithosphere. The biotic sphere is named the biosphere. Because these four spheres aren't independent units in nature, their boundaries must be understood as transitional instead of sharp delimitations.
Atmosphere (discussed above)
Hydrosphere
The Earth’s water, which exists in both fresh and saline form and should occur during a liquid, solid or gaseous state. Land, sea and air each contribute to the entire volume of water, which is conveyed between various locations and transformed from one state to a different (Hydrological Cycle). The general quantity of water within the hydrosphere remains more or less constant.
About 71 per cent of Earth’s surface is occupied by water. Some 97.3 per cent of its volume is currently within the ocean, the utmost extent of which is within the hemisphere. Of the 2.7 per cent terrestrial water, most are polar snow and ice. Groundwater (the majority below soil level) is in lakes and rivers.
Lithosphere
The zone, incorporating elements of the hydrosphere, lithosphere and atmosphere, during which life occurs on Earth is that the biosphere. The intricate, interconnected web that links all organisms with their physical environment is understood as the biosphere (ecosphere). The biosphere extends from the rock bottom of ocean trenches to about 8 km above the ocean level. The term is occasionally wont to refer only to the living component alone, although it's more commonly conceived as a zone of interaction between the opposite ‘spheres’. this is often appropriate because life depends upon energy, processes and materials which are located altogether three of the Earth’s other conceptual spheres, to the extent that the scheme is usually represented as a series of overlapping hexagons with the biosphere within the nodal position. utilized in this manner, the biosphere is synonymous with the ecosphere. The biosphere has evolved, reorganised itself sometimes, faced extinction, gained new vitality, and managed to flourish overall. Earth’s biosphere is that the just one known within the Solar System; thus, life, as we all know, is exclusive to the world. Today, nearly seven billion humans, approximately a million animal species and 355,000 known plant species, depend upon the air, water and land of the earth Earth.
Biosphere
The zone, incorporating elements of the hydrosphere, lithosphere and atmosphere, during which life occurs on Earth is that the biosphere. The intricate, interconnected web that links all organisms with their physical environment is understood as the biosphere (ecosphere). The biosphere extends from the rock bottom of ocean trenches to about 8 km above the ocean level. The term is occasionally wont to refer only to the living component alone, although it's more commonly conceived as a zone of interaction between the opposite ‘spheres’. this is often appropriate because life depends upon energy, processes and materials which are located altogether three of the Earth’s other conceptual spheres, to the extent that the scheme is usually represented as a series of overlapping hexagons with the biosphere within the nodal position. utilized in this manner, the biosphere is synonymous with the ecosphere. The biosphere has evolved, reorganised itself sometimes, faced extinction, gained new vitality, and managed to flourish overall. Earth’s biosphere is that the just one known within the Solar System; thus, life, as we all know, is exclusive to the world. Today, nearly seven billion humans, approximately a million animal species and 355,000 known plant species, depend upon the air, water and land of the earth Earth.
References :
Environment and Ecology by Majid Husain.
Images are from freepik.com.
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