Nature and Natural Processes!
The Earth in the Solar System:
The sun is one of the 100 billion stars belonging to the MILKY WAY galaxy. The solar family of nine major planets and at least a thousand tiny planets known as asteroids is dwarfed and dominated by the SUN. The sun contains over 99.87% of the total mass in the solar system.
In spite of their comparative smallness and the enormous distances of empty space that separate the planets from the sun as well as from one another, the sun keeps its planets under rigid control. Every planet revolves around the sun continuously, in their own specific elliptical orbits.
These planets are held near the sun by the pull of gravity. They are kept from being drawn into the sun by the tremendous speed with which they revolve through space. The lesser the distance from the sun, the faster they move.
The Earth is the only planet in the solar system known to support living creatures. This is because the Earth’s composition and distance from the sun have provided exactly the necessary conditions for the evolution to an advanced form of life. The Geocentric Theory refers to the ancient and medieval times when it was thought that the earth was the centre of the universe. This traditional belief was demolished by Copernicus. He said that the earth was one among the many planets in a sun-centered system. This is the Heliocentric Theory. Today, it is no longer a theory but an established fact.
During the past two hundred years, a number of theories have been advanced regarding the origin of the earth:
(i) The Nebular Theory of Kant and Laplace. In the 18th century, they said that the solar system originated from a hot, rotating, gaseous mass which contracted while cooling and thrown off rings of matter which condensed to form planets.
(ii) The Planetesimal Hypothesis put forward by the Americans — Chamberlin and Moulton. They supposed that the planets originated through the coalescence, by gravitational attraction, of planetesimals or fragments of solar material.
(iii)The Tidal Theory of Jeans says that a wandering star came near the sun and produced a tidal distortion in the sun. This resulted in a cigar-shaped filament of solar matter being pulled away from the sun. In due course, this materialized into concentration of planets.
(iv) The Twin-sun Theory put forward by Hoyle, according to which the solar system was derived from the sun’s former twin which exploded and shattered. Following the explosion, some of the materials became concentrated into planets due to gravitational attraction.
Composition and Structure of the Earth:
The earth can be compared to an onion, because it is made up of a series of “shell” or onion-like layers. These layers (lithosphere) are composed of different materials. There are differences in views regarding the number of layers, their constitution and thickness.
The following is the generally accepted interpretation of the composition and structure of the earth:
(a) The Crust:
This is the outer layer of the earth. It is composed of crystalline rocks with sedimentary rock clippings. The depth of the crust is about 20 to 30 miles (32.2 to 48.3 km). The specific gravity of the rocks vary between 2.0 and 3.0. The crust or outer zone is separated from the zone underneath by a distinct break. This discontinuity is the MOHOROVICIC DISCONTINUITY.
The crust is distinguished into 2 layers:
(i) Sial:
This is the outer layer. It is made up of sedimentary and granitic rocks. The name comes from silica (Si) and alumina (Al).
(ii) Sima:
This is the underlying layer. It is made up of dense basaltic rocks. The name comes from silica (Si) and magnesia (Ma).
The Mantle:
This is the middle layer which is composed of ultrabasic rocks, it is said that the mantle consists of the mineral olivine. Olivine is a heavy silicate of magnesium and iron. The specific gravity of the rocks here vary between 3.0 and 5.0. The mantle extends downward to a depth of about 1,800 miles (3,000 km). The mantle is separated from the core (or centre) of the earth by the Gutenberg Discontinuity.
If the mantle is further subdivided, we will find an interesting layer near its outer margin. This is the Asthenosphere or Low Velocity Layer. The asthenosphere is found at depths of between 50 km 250 km. It supposedly contains partially molten material.
The Core:
It occurs at depths below 2,900 km.
From various evidences found so far, the core may be divided into 2 zones:
(i) An outer core which exists in a liquid or plastic state; and
(ii) An inner core which is most probably solid.
It is assumed that the core is composed of a nickel-iron mixture. Hence, it is known as NIFE. We know that both temperature and pressure increase with depth, as one penetrates below the earth’s surface. Therefore, although the earth’s outer crust is solid, the material at the earth’s centre will exist in a molten or gaseous state.
Composition of the Atmosphere:
Air is not a chemical compound. It is a mechanical mixture of gases. Four gases — nitrogen, oxygen, argon and carbon dioxide — make up 99.98% of the air by volume.
In general, the atmosphere can be said to be composed of:
(a) Gases
(b) Water vapour
(c) Dust particles.
(a) From the table we see that the principal gases comprising dry air at sea level are nitrogen, oxygen, argon, carbon dioxide, neon, helium, ozone, hydrogen, krypton, xenon and methane. Out of these gases, there are some that are so inert chemically that they are never found in any chemical compound. These gases are argon, neon, helium, krypton and xenon.
(b) Besides these gases, water vapour, which varies with time and space, is a vital constituent of the atmosphere.
(c) Aerosols are present in the atmosphere in significant quantities. Suspended particles of dust, sea-salt, organic matter, smoke etc. are collectively called aerosols.
The Hydrosphere:
The hydrosphere for the most part fills the depression of the rock sphere, but because of its penetrative qualities some water is found in the rocks and much exists in the troposphere in the form of water vapour. The oceans, which cover about 72% of the surface, contain the great bulk of the water.
The average depth of the oceans is about three kilometers (containing 350,000 plant species and 11 million animal species). The general level of the ocean floor — so-called deep-sea trenches — parallel some of the continental margins and island areas.
The Biosphere:
If we try and glance over the surface of our earth, we will see life everywhere on land and in the oceans. On land, life exists from sea-level to an altitude of 3,000 meters; abundant evidence of life is found in the upper 100 meters of the oceans. Life also extents up to a depth of 10,000 metres beneath the oceans, as well as in the upper reaches of the atmosphere and high mountains, up to an altitude of almost 10,000 meters. The biologically inhabited part of the hydrosphere, lithosphere and atmosphere together constitute the biosphere.
What is the Biosphere?
Biosphere is the component part of the earth that includes all forms of organic life which require food for continuing all life activities. Thus, the sphere of living matter, along with the layer of water, air and soil surrounding it on the surface of the earth is termed the “biosphere”.
Why do we need to study the Biosphere?
One should study the Biosphere with a definite purpose in mind.
The various ways in which the study of this subject may help us have been summarized as follows:
(i) Identification and assessment of the impact of man’s actions upon the biosphere and conversely to those of the biosphere on man.
(ii) Analysis and comparison of the functioning of the natural modified and managed ecosystems on a global scale.
(iii) Development of ways and — means to monitor and measure both quantitative and qualitative alterations in the environment in order to establish scientific criteria that will provide a base for rational management of natural resources and also establish standards of environment quality.
(iv) Promotion of development and application of computer simulation and other approaches which will help the predictions of likely future trends, allowing mankind to direct its action for long-term best interests.
(v) Development of study material for environmental education at all levels and stimulating global awareness about environmental problems with the help of the public media.
Subject Matter of Study of the Biosphere:
The study of the biosphere includes:
(i) Ecological effects of increasing human population and activities on tropical and subtropical ecosystems.
(ii) Ecological effects of various land use and management practices on Mediterranean and temperate forest ecosystems.
(iii) Impact of man’s activities, especially irrigation practices, on the sensitive arid and semi-arid regions.
(iv) Impact of man’s activities on the value and resources of water-bodies and wetlands.
(v) Human activities and related environmental problems affecting the society.
(vi) Genetic and demographic changes resulting from changing environmental conditions.
Dynamics of the Biosphere:
Unlike inorganic life, organic life, i.e. plants, animals etc., need food to continue their existence. The principal food that the organic life needs is carbon, which maintains life by providing heat. The atmosphere happens to be the original sources of carbon. Plants and other forms of vegetable life can take carbon directly from the atmosphere. However, animals get the required carbon from the vegetables and the animals (feeding on the vegetable matter) that they consume.
The Process of Photosynthesis:
The process of photosynthesis forms the primary pathway by which plants withdraw carbon from the carbon dioxide pool and utilize it to build essential carbohydrates and other organic compounds. In order to understand the relationships between different organisms in the universe, we should understand the energy flow in the earth as a whole. To do so, we must consider here the first and second laws of thermodynamics.
The first law states that energy can be neither created nor destroyed; it is transferred or transformed into different forms.
The second law states that during energy transformation, energy changes from a concentrated to a dispersed condition.
These laws explain the production of living tissues and the succession of living plant tissue. Solar energy is utilized and combined with essential materials in the process of photosynthesis, as shown in the following reaction:
CO2 + H2O + Minerals + Sunlight → Organic matter + O2 + Heat
Photosynthesis is critical to life on earth, since it removes carbon dioxide from the atmosphere and substitutes oxygen. Human cannot live as they do in an oxygen-deficient atmosphere. When the organic life does not have the amount of food it requires, or it cannot assimilate the food due to some defects in its “food-manufacturing machinery”, it leads to its “death”. The death is followed by disintegration and, finally, the matter is returned to the atmosphere, its original home. Thus the “Cycle of Life” between the atmosphere and the organic forms is completed.
Energy Flow in the Ecosystems:
In any ecosystem, energy in the form of food passes through a number of stages, or Tropic levels, thus forming a Food Chain. Energy from sunlight is taken up by autotrophs (food-producing plants), which, in turn, produce carbohydrate, or the food substance, by photosynthesis.
These autotrophs again provide sustenance to the herbivores, and the carbon stored in the carbohydrates manufactured by the autotrophs is transferred to the animals. The herbivores are eaten by the carnivores, and the carbon continues its journey further along the food-chain. By the complex biochemical process called respiration, plants and animals extract necessary energy from the organic compounds.
Division of Organic Life:
We can divide Biosphere, or the organic life, into three principal classes. This division is based mainly on the degree of the freedom of movement and the possession of some organs that are specially developed.
The classes are:
(1) Plant Life
(2) Animal Life
(3) Human Life.
Unlike animals and humans, plants are fixed to the ground where it was formed by its roots. On the other hand the intellect of man is far more developed than that of any animal. However, none of these forms of life remain confined to any particular region or locality.
Animals and humans have their own organs of locomotion that carry them from one place to another. But in the case of plants, various agents, such as water, wind, birds or man may take the seeds from place to place. If the environment is favourable the seeds may germinate in a new region. This is how plant life spreads.
Bio-Geo Chemical Cycles:
The energy required for the maintenance of living organisms comes from sunlight. However, only this is not sufficient. The materials needed for the existence of living things are provided by the Earth. Bio-geo chemical cycle involve the cyclic movement of material or nutrient. The term is so since the cycling of elements involve biological organism (bio), geological environment (geo) and the chemical changes.
General Characteristic Features of Bio-Geochemical Cycles:
The significant features characteristic of bio-geochemical cycles is:
A bio-geochemical pool is a quantity of any chemical substance, either in a biotic, or in an abiotic component of an ecosystem. For instance, the atmosphere contains an enormous pool of carbon, in the form of carbon dioxide gas, while the ocean waters contain carbon in the form of dissolved bicarbonate. Carbon is contained by calcareous rocks in the form of particulate carbonate. Living organisms contain carbon as organic matter.
The flux rate, i.e., the quantity of material which is passing from one pool to another, per unit time and per unit area or volume of the system.
Turnover rate is the flux rate into or out of a pool, divided by the quantity of nutrient in the pool. This allows the importance of the flux process to be determined in relation to pool size.
Turnover time is the quantity of nutrient in the pool, divided by the flux rate. It indicates the time necessary for the movement of a quantity of nutrient equal to that in the pool.
Classification of Nutrients:
According to their importance as structural parts of organic matter, elements essential for life can be classified into three categories.
These categories and their constituents are shown in the table:
However, other workers have identified major constituents macro- and micro- constituents.
(1) Major constituents — are most important in the bio-geochemical process of the earth.
(2) Macronutrients are those elements and compounds that are needed by living organisms in large quantities and are major constituents of protoplasm.
(3) Micronutrients are those elements and compounds that are indispensable for the functioning of living systems, but are needed in only small quantities.
Types of Bio-Geochemical Cycles:
(1) Gaseous Nutrient Cycle, associated mainly with the atmosphere and ocean. Such are carbon, oxygen and nitrogen cycles.
(2) Sedimentary Nutrient Cycle, where the lithosphere or sedimentary rock is the nutrient reservoir.
As per syllabus only three gaseous cycles have been discussed — carbon cycle, nitrogen cycle and oxygen cycle.
The Carbon Cycle:
The carbon cycle is probably the most important, as well as the simplest of the gaseous cycles. It is said to be the perfect cycle, in which the carbon is returned to the atmosphere almost as fast as it is removed.
The movement of the carbon occurs from the atmospheric reservoir to the producers, then the consumers, and from them to the decomposers, then back to the reservoir.
The two principal components of the carbon cycle are carbon dioxide and organic carbon.
Reservoir:
(i) The atmosphere is the gaseous reservoir in the carbon cycle. It has a carbon concentration of 0.03%. Almost 2.5 x 1010 tons of carbons are annually removed by the terrestrial organisms. Marine organisms remove about 1.9 x 1010 tons. If we also consider the removal by fresh organisms, the annual withdrawal of carbon is almost 9 x 1010 tons.
(ii) The sea is the second major reservoir of carbon. When salinity of sea water is 35 gms per kilo, CO, content is 47 cc per liter.
Withdrawal of CO2 from the Atmospheric Reserves:
The primary producers or green vegetation play the most significant role in drawing the CO2, from the atmosphere and/or the hydrosphere, and then helping to build up organic carbon from inorganic sources.
This can be represented by the equation below:
This carbon is then carried further in two ways:
(a) By Food chain through herbivores and carnivores, and
(b) By Geologic sources.
Plants combine a portion of the carbon with oxygen, nitrogen, sulphur and phosphorus. In this way proteins are formed. The proteins then move through the food chain until they reach the decomposers. The geologic component of the system deals with the deposition of plant material, which is later formed into peat coal and oil. There are also aquatic organisms that fix CO2 directly from dissolved salts in the water. Also, CO2, is removed from the atmosphere by precipitation.
Return of CO2 to the Atmospheric Reservoir:
A considerable amount of the biologically fixed CO2 is returned to the atmosphere by the respiratory activity of the producers and consumers.
The most substantial return of CO2 to the atmosphere is contributed by the respiratory activity of the decomposers that work upon dead and decaying organisms and fecal matter.
Return of CO2, from the biota also occurs through the non-biological process of combustion. This happens in fire-wood burning, forest fire or accidental building fire, and so on.
Another source is geologic, when burning of fossil fuel gives back the carbon that had been locked in the rock strata over the years. The same is also done by volcanoes, hot springs and fissures in the rocks.
With the advancement of civilization, CO2 emissions have increased due to industrial and agricultural activities. The dissolution of sedimentary rocks (formed by calcium carbonate depositions), when available to the aquatic environment, may return the carbon to the atmosphere.
Increase of CO2 in the Atmosphere:
The amount of CO2 injected into the atmosphere is small in comparison to the total CO2 in circulation. Yet, this is having a perceptible effect. This is because the atmospheric reservoir is small and large oceanic reservoirs cannot absorb the new CO2 as fast as it is being produced.
There has been a steady rise in the CO2 content of the atmosphere during the 20th century. The generally accepted value is now 0.055%.
Conclusion:
Thus, the carbon cycle is considered to be an important cycle, especially in productivity, pH and alkalinity. There are numerous ways in which carbon is utilized, as well as restored to the atmosphere. The extent to which the system will regulate or adapt itself to the present rise in the volume of release of CO2 is still a question.