What is Atmosphere? Describe the Composition of Atmosphere.


Atmosphere is the gaseous mantle around the lithosphere and hydrosphere. It constitutes a number of gases such as nitrogen, oxygen, argon, carbon dioxide, neon, xenon, ozone, and knyton. These gases have definite percentage in the atmosphere in normal conditions. In addition to this, atmosphere also includes water vapours, dust particles, industrial gases, pollen, and several other micro-organisms carried particles.

Lithosphere is mainly made up of the solid components and constitute rocky substance. Hydrosphere includes the liquid components such as lakes water, water, ocean and ponds.

These three subdivisions of the environment are the main sources of energy for plants and animals. They affect the metabolism in various ways. The atmosphere provides various gases like oxygen, nitrogen, carbon dioxide, lithosphere provides all minerals and hydrosphere provides water.

The global environment consists of three main subdivisions:
(i) Hydrosphere (ii) Lithosphere (iii) Atmosphere

The hydrosphere includes all liquid components, i.e. , water in oceans, lakes, rivers, etc.

The lithosphere comprises the solid components, i.e. , the rocky substances of the continents.

The atmosphere is the gaseous mantle which envelops the hydrosphere and the lithosphere.

Living organisms require inorganic metabikutes from each of these sub-divisions. The hydrosphere supplies liquid water, the lithosphere supplies all other minerals, and the atmosphere supplies oxygen, nitrogen and carbon dioxide.

Together, these inorganic materials provide all the chemical elements needed in the construction and maintenance of living matter. In addition to being source of supply, the three sub-divisions of the environment also affect metabolism in various other specific ways.

The Hydrosphere: Water is the most abundant minerals of the planet. It covers about 73 percent of the earth’s surface and it is the major constitute of lithosphere and the atmosphere. Water is also the most abundant component of living matter and therefore it is the major inorganic nutrient required by all living organisms. In metabolism, water is the exclusive source of the element hydrogen and one of the several sources of oxygen. The basic water cycle which moves and conserves water in the environments is quite familiar.

Solar energy evaporates water from the hydrosphere into the atmosphere. The vapours thus produced are cooled and condensed at higher altitudes, produce clouds, and precipitation as rain or snow then return the water to the hydrosphere. This is the most massive process of any kind of earth, consuming more energy, moving more material than any other.

(1) In using water as metabolic raw material, organisms withdraw it principally from the hydrosphere. Aquatic organisms absorb water directly from their liquid environment; they excrete some of it back while they live and after death, the remainder, still in the form of liquid water, is returned through decay. Terrestrial organisms absorb liquid water from the reservoir present in the soil and in bodies of fresh water. Plants and animals move such water through their bodies and in the process they retain required quantities.

(2) Water influences metabolism not only through its function as a prime nutrient but also through its effect on almost all aspects of climate and weather, both in the sea and on land. In the ocean, water warmed in the tropics becomes light and rises to the surface, whereas cool polar water sinks. These up-down displacements bring about massive horizontal shifts of water between equator and pole. The rotation of the earth introduces east- west displacements. These effects, reinforced substantially by similar patterned wind-producing air-movements, result in oceanic currents. The latter influence climatic condition not only within the seas, but also in the air and on land.

(3) Climatic effect is a result of the thermal properties of water. Of all liquids, water is one of the slowest to heat or, cool, and it stores a very large amount of thermal energy. The oceans thus become huge reservoir of solar heat. The result is that sea air-chilled by night, becomes less cold because of heat radiation from water warmed by day. Similarly, sea air-warmed by day becomes less hot because of heat absorption by water cooled by night. Warm or cool onshore winds then moderate the inland climate in daily patterns. More profound effects are produced by heat radiation and absorption in seasonal summers and winter patterns.

(4) Global climate over long periods of time is determined by the relative amount of water locked into polar ice. As the polar ice is melting, water levels are now rising and coast lines are gradually being submerged. If trend during the past 50 years are reliable indications, the earth appears to be warming up generally. Deserts are presently expanding, snowlines on mountains are receding to higher altitudes; in given localities, more days of the year are snow free; and the flora and fauna native to given latitudes are slowly spreading poleward. It is difficult to be sure whether these changes are merely part of a short warm cycle or are really indicative of a long-range trend.

All these various cyclic changes in the hydrosphere have profound impact on metabolisms.

The Lithosphere : This sub-division of the environment plays two vital roles in metabolism:
(a) It is the exclusive source of most mineral metabolites for all organisms, terrestrial as well as aquatic; and
(b) It forms the bulk component of soil, required specifically by terrestrial plants.

Minerals and Cycles: Like the world’s water, the rocky substance of the earth’s surface moves in a huge cycle, but here the rate of movement of cycle is measured in thousand and millions of cycle. One segment of this mineral cycle is diastrophism that is the vertical uprising of the large tracts of his earth crust. Large number of the parts of the continent or the whole continent may undergo such diastrophic movements. These movements may occur when a land mass is pushed up from below. The changes thus occur are very slow. The important instance of diastrophism is mountain building. The youngest and highest mountain ranges are the Himalayas, the Rockies, the Andes, and the Alps. All these were uplifted some 75 million years ago and we may still now note that the earth’s crust in these regions is not completely settled.

This type of uplifting of the mountains, or formation of mountains has long lasting effect on climate, and consequently on the metabolism.

Segment of the global lithospheric cycle involves gradation that is the lowering of high land and the levelling of mountains. These changes are brought about in past by actual geologic sinking of land and in part by the action of the hydrosphere and the atmosphere. These actions usually take the form of erosin and dissolution of rock. There are many instances of erosional processes.

Accompanying the physical forces of gradation are chemical forces which are of particular importance.
1. There are the chemical action of water and chemical processes which accompany the major erosional factors. They contribute to breaking large stones into smaller ones and small pebbles into tiny sand grains and microscopic rock fragments.
2. Whenever water is in contact with rock, it dissolves small quantities of it and thus acquires a mineral content. The dissolved minerals are carried largely in the form of ions.

The dissolved soil minerals ultimately drain back into the ocean. It was partly by this means that the earlier seas on earth acquired their original saltiness, and as the global water cycle now continues, it makes the oceans even saltier. The mineral icons in the ocean are used freely by the organism as metabolites.

The lithospheric cycle supplies many more types of minerals than organism normally require. Those withdrawn and used by most organisms include, e.g., ions of nitrates, chlorides, carbonates, sulphates, and ions of sodium, potassium, managanese, copper and iron.

Soil: We have thus noted that lithosphere plays a special role in the metabolism of land plants in that contributes importantly to the formation of soil. This complex material serves in plant maintenance in two-ways:
(a) It provides mechanical anchorage for plants.
(b) It holds water and mineral ions, the source from which land plants obtain supplies of these inorganic nutrients.

The major components of soil was contributed by living organisms. Early terrestrial organisms which did not require soil themselves shed their excretion products into the sand layers, and upon death their bodies came to be added as well.

One of the main reasons why such a vast host of animals has colonized the soil is because it provides an insurance against the danger of desiccation. Few soil species can live above ground for long and those that do so have to adopt some means of protecting themselves during dry weather. It is significant that sandy soils never support as many animals as those containing a high proportion of humus and some clay. Thus water content of a soil and the amount of organic matter present, together provide a reliable index for predicting the density of animal colonization. The upper layer of the soil is generally referred to as topsoil. The roots of the small plants are embedded entirely in topsoil. The chemical value of a soil depends upon its usable water and mineral content. Soil particles are enveloped by thin films and water.

Explain the four Zones of Atmosphere?

Atmosphere can be roughly divided into four zones.

(1) Troposphere : It is about 20 km above the earth surface. In these important events such as cloud formation, lightning thunder storms and thundering all take place in this sphere:

(2) Ionosphere : The rest above the mesosphere upto height of 400 kms above the earth’s surface is ionosphere. Most of the gases are present in the form of ions.

(3) Stratosphere : It is next to troposphere. It is about 30 kms above the troposphere, is called as stratosphere. In this zone ozone formation takes place, under the influence of ultra violet component of sunlight.

(4)Mesosphere : About 40 km in height above stratosphere is called mesosphere. In this zone temperature shows again a decrease upto 80°C.