Geology - Interior of the Earth

Lithosphere :- The solid Earth is known as Lithosphere. An idea about the constituents of this solid body of about 6370 km radius , can be had on the basis of several available indirect observations. Say for example , the average density of the whole earth is 5.5 , whereas that for the rocks making most of the upper crust of the Earth is 3 , which infers that the material beneath the surface is of a much higher density. The temperature indications show that it increases with the depth. The hat lava erupted by the volcanoes also indicates that the deep interior parts of the Earth are very very hot. The pressure as also been observed to be increasing with depth. An analysis of the meteorites falling on earth indicates that they essentially consist of iron and nickel in their core. Since the earth is also a celestial body like That of the meteorites , it can be easily inferred that out of Earth may also contains iron and nickel in it's core.
From all such indirect evidence , it has been generally established that the matter inside the earth is of a higher density , and the deep interior part of the Earth may be in liquid state ; or because of high pressure , it may be in semi-liquid state.
In the modern times , however , our knowledge regarding the interior of the Earth has been vastly increases by the experimental results obtained with the help of seismic waves. During an earthquake ( natural or artificial produced by an explosion ) , three types of waves are generated , known as primary (P) , Secondary (S) , and Long (L) waves. These waves radiated in all directions passing through the earth body , moving faster in the higher density medium. The L - waves which confines themselves to the crystal part , travel faster along the ocean floors. This indicates that the ocean floor composed of a material denser than that of the upper crust of the continent basins. The P and S waves which propagate through the deeper parts of the Earth , are subjected to reflection and refrection with the changes in density. The S-Waves are further characterised by their capablity of passing only through the solids. 
Based upon such experimental work, carried out with the help of such seismic waves , the interior of the Earth can be predicted today , with an enough degree of confidence.
In all , the entire 6370 km thickness of the Earth can be divided into the following three major zones :-
(A) The Crust
(B) The Mantle
(C) The Core

(A) The Crust :- The topmost thin layer of the earth body , having solid thickness of about 30 to 40 km In continents and 5 to 6 km in the oceans , is known as the crust. The base of the crust is marked by a sharp boundary , called Mohorovicic discontinuity or M - discontinuity. The depth of the M - discontinuity is greater beneath the continents than beneath the ocean basins.
Intact , it has been concluded that in the continents , the total depth is about 35 km , out of which the bottom of 5 km depth consists of denser Basalt rock ( density = 3.0 ) , and the top 30 km consists of lighter Granite rock ( Density = 2.7 ) . There is no such granite beneath the oceans , and only 5-6 km thick basalt occurs. These granitic rocks of the continents and the basaltic rocks of the oceans , are generally covered by a top layer of unconsolidated sediments deposited since the formation of these continents or oceans.
The earth crust thus provides us with very useful hard and soft rocks , and are classified as , Igneous , Sedimentary , and Metamorphic rocks , depending upon the certain factors.

(B) The Mantle :- Beneath the M - discontinuity , lie the still denser rocks ( average density 3.3 ) known as the ultra basic rocks , and this portion of the earth is known as the Mantle. It's thickness is about 2860 km and it's density increases with depth.

(C) The Core :- Below the depth of about 2900 km from the surface of the earth , starts the cores. It has been inferred by the study of seismic waves that the earths core is probably 12 or more , but it's exact compositions is not known. Most of the scientists is favour in iron - nickel composition , while some other support the idea of iron - silicate core.
An abrupt increase in the velocity of P - waves at about 2170 km below the core boundary , suggests the presence of an inner core.
This may mean a change from the liquid to the solid state , but this is not well established fact.
The presence of earth's magnetic field may also be explained under this theory of the presence of a liquid core. This may be due to the electric current set up by motion in the liquid core. This is possible because the core is thought to be metallic and , therefore , a good conductor.

Geology - The Exterior of the Earth

We know that the gaseous layer encircling the Earth outside it's surface is called the atmosphere. This gaseous environment extends to about 500 km beyond the Earth surface. Although , extending to far such large distances , this atmosphere weighs only about one millionth part of the weight of the Earth. This is because of its gaseous composition.
This atmosphere has been established to be consisting of layers of different environments. As such , it can be divided into the following four zones :-

(1) Troposphere :- It is the nearest gaseous zone extending from the surface of the earth upto a average distance of about 11 km at the poles and 17 km at the equatorial regions.
Temperature decreases with the height in the troposphere , since the main heat source is the solar radiations which is absorbed at the ground level. The rate of decrease of temperature , called the lapse rate , is about 5* C/km. The troposphere contains most of the water vapour , clouds , and storms of the atmosphere Winds tend to be the strongest at the tropopause , the level of the jet streams. This is also the level at which the jet aircrafts cruise. The troposphere contains about three-fourth of the total weight of the atmosphere, and is responsible for the most of the meteorological processes. Thus it is the troposphere , in which winds are generated and clouds are formed , which cause precipitation.

(2) Stratosphere :- Above the tropopause (at about 10-16 km altitude) lies another zone , called the stratosphere , extending upto about 50 km altitude , to a point called the stratopause. Between the tropopause and stratopause , the temperature increases gradually with height , from about - 80*C to about 0*C or so. At the stratopause , the temperature , infact , is about as heigh as at the ground level. It's warmth due to the absorption of ultraviolet radiation from the sun by oxygen and ozone. Most of the worlds ozone is found in the stratosphere , where it may exceeds 5 ppmv (parts per million by volume). Hence , stratospheric air is lethal to human beings. There is very little water vapour at these heights. Ozone is , infact , formed in this zone due to the splitting of an oxygen molecule into the atomic oxygen and it's subsequent union with an oxygen molecule to form Ozone. Ozone is , however , destroyed naturally by ultraviolet radiation , as it helps in preventing ultraviolet radiation from the reaching the ground. In the stratosphere , ozone is , thus , constantly being formed and destroyed , and is , therefore , maintained in a rough equilibrium , under natural unpoluted environment.
Since , ozone is formed in the stratosphere , this zone is also sometimes called as the ozonosphere. The ozonosphere is of utmost importance to life on the Earth. As it absorb most of the ultraviolet radiations from the sun , which in its absence , would possibly have burnt all the life on Earth.

(3) Mesosphere :- The Mesosphere extends from the stratopause at about 50 km altitude and at about 0* C to another temperature minimum of about - 110* C at about 80 km altitude. This top boundary of Mesosphere is called mesopause. The atmosphere in this zone is windy and turbulent , but there is usually too little water vapour for clouds to form.

(4) Thermosphere :- Above the mesopause ( 80 km altitude ) the temperature increases indefinitely upward into the Thermosphere ( I.e the hot upper atmosphere ) , which zone may extend upto about 500 km altitude.
The Mesosphere and the Thermosphere zones contains many ions and free electrons. Cosmic rays and radiations from the sun produces these ions. Both these zones together are , therefore , usually referred to as the ionosphere. The ionosphere is very light in mass , despite having a large volume.
The region of atmosphere beyond about 500 km , is called exosphere , and till today , very little is known about it. It is perhaps a low density , high temperature region , with minimum atomic collisions.
As far as the chemical compositions of the atmosphere is concerned , it has been found to be mainly a mixture of approximately 78% Nitrogen and 20% oxygen by volume. Other gases like carbondioxide , argon , neon , helium , ozone and water vapours will be constitute the balance 2 % . This consumption is fairly constant in the region of troposphere and a large part of stratosphere. Dust particles and liquid droplets are also found present in the lower atmosphere , and water vapours may be present in large variation.

GEOLOGY - The Possible End of the World. How and When ?

What is the future and fate of the unique planet on which we live ? This is a question which the scientists are trying to answer in the modern days of advanced technology. Well intact , with any amount of advanced science , it is not possible to give a correct precise answer to this question. What actually will be the end of our earth , is the question which time alone will tell. Man , however , due to his inherent curiosity , cannot wait and see , and is therefore , trying to speculate or theorize on this issue , just as he did on the issue of the origin of the earth.
Many astronomers have tried to find out suitable answer to this riddle. Most of them try to connect the life of the earth with the availability of heat and light from the sun. Indeed , if we were not so much depend upon the sun , perhaps , in most probability , the earth might have last for ever.  But since , earths life is very much dependent upon the sun , it will possibly end , as and when the Sun's nuclear fuels gets exhausted and it stop radiating energy.
On the basis of the studies of the older stars that resembles our sun , it has been seen that when the aging stars begins to run out their nuclear fuels , they starts burning and ultimately become dark. On the same analogy , our sun also be one day behave in the same fashion , and thus in most probability , the end of our earth will come in the following manner :-

When once the original hydrogen of the sun gets converted into helium , it's core will begin to contract. And as the core shrinks , it will generate sufficient heat to start thermonuclear reactions capable of producting incredibly high temperatures. These nuclear furnaces may cause the body of the sun to expand , and thus gradually increasing the amount of heat and light radiation. This accelerated radiation should cause the sun to become hotter and hotter , and redder and redder , till it becomes a red giant-a mass of red hot , rarefied gas. During this stage of expension of the sun and it's great heat releasing powers , the two nearby planets I.e Mercury and Venus may completely get vaporised and lost. As regards the 3rd and 4th planets I.e Earth and Mars is concerned , it is possible that they may also get vaporised , may avoid that fate in Toto due to their greatest distance from the sun. In any case , the earth will not escape the deadly high solar temperatures , the oceans will boil , the rocks melted , and life destroyed.
The future of our sun and earth upto this stage is quite certain although scientists cannot precisely define the events that would follow this. In all probability , after reaching the climax of hot red gaint , the will steadily diminished in brightness and energy , and end itself into a white dwarf. This is possible , because we have seen stars that have completely exhausted their supply of hydrogen and other nuclear fuel , and shine only because of their internal heat. As a white dwarf , the sun will continue to radiate its energy , and will gradually get cooled and contracted. In due time , it will probably shrinks to the size of a planet , and become cold and dark.
With its fires gone out , the sun and planets of the solar system will become at the mercy of the icy temperatures of the interstellar space. At these temperature of hundreds of degrees below the freezing , gases will be converted into liquids , and liquids will become solids , and thus , earth will eventually become a dark frozen mass.
It is , however , very much possible that even in death , the sun will continue keeping its hold on the remaining planets , which will continue to revolve around this cold inert sun. This is because the sun's mass and gravitational force will remains strong enough to keep the remaining planets locked in eternal orbits around it.
After predicting , as to how the earths end will come , we are now left with the possible timing if this occurrence. When will these predicted solar changes occur ? Well , the present and nearby population of the world has no cause to worry , because it's seems possible that the life on earth will further continue to flourish for at least 5 billions years , perhaps even longer. This time period has been based on the assumption that medium sized stars , like the sun , radiate at least 10 billions years , before the hydrogen fuel of their core is exhausted. Thus , the sun , which , at present , is about 5 billions years old , is in its 'middle age' and will continue for a further period of about 5 billions years.

GEOLOGY - Earth and Origin of Earth

We know that the Earths place in the universe is indeed small , and compare to the other planets , it is not too large in size. Even inspite of that , Earth is a sizeable body , with a polar diameter of about 12, 714 km , and equatorial diameter of 12,756 km , and thus has an equatorial bulge. The circumference of the earth is about 40, 000 km , and it's surface is area is about 510 million square km. Its volume is about 1042 billion cubic km , and it's mass is about 5.97 into 10 is power 21 tonnes. In shape , the earth is like an oblate spheroid. That is , with the exception of a slight flattening at the poles , the earth is nearly spherical or ball shaped. The minor flattening or earth's equatorial bulge is caused by the centrifugal force of rotation. This midriff bulge of earth is very minor in the sense that on a model earth of 8 metre in diameter , one could hardly see it , for this slight protuberance would amounts to less than 2 cm. On the same scale ,  our highest mountains would rise to about 1/2 cm above the sea level.
But deposit it's relatively unassuming statistics , ours is a most fortunate planet the seems "just right" in many ways. Its general size , composition , daily rotation and it's distance from the sun perhaps provides optimum conditions for the development and continuation of life. The fact that earth is the only planet that appears to have a large supply of water , has undoubtedly had much to do with this. Earth's No. 3 position is also very important , for at about 150 million km from the sun , it is neither too near it , nor too far off it. Has it been very near to the sun like mercury , the heat and temperatures would be enormously high and seas would have literally boiled away. On the other hand , if it would have been too far away like Pluto , there would be incredibly cold , making life impossible. Earth's average of temperature of 14 degree celcious appears to be "just right" for life sustenance.

Origin of the Earth :- We human beings have been living on the Earth for a very long time. During the development of science on the Earth, and in his search to know the unknown, man has thought to a lot to know as to how Earth was born. Where from it come ? This question , which has kept the minds of the cosmogonists agitated for a long time , can not be answered with certainty , even till to day.
Infact , the problem is not only to predict the origin of the Earth , but is to predict the origin of the entire solar system , of which , Earth is an important member. Therefore , any speculative suggestion made on the mode of this origin , must satisfy all the known facts about our solar system , and it must agree quantitative with all the known physical and chemical laws.
Intact , our solar system is a well ordered system of planetary bodies , and is not just a haphazard arrangement. This fact may indicate a common origin for all the components of this system. Hence , the entire solar system should be viewed as a whole together , abducted any prediction made regarding the origin of any of its component should be satisfy all the known characteristics of the entire solar system as a whole.

GEOLOGY - Universe and the Solar System

The earth on which we are living is a 'remarkable' astronomical body in the entire universe , even though it is neither the largest or the heaviest , nor the fastest or the slowest member of our solar system. It is , intact , a very insignificant component of our solar system , which consist of nine major planets (including the earth) moving around a central body - the sun. Besides these nine major planets, there are 32 moons or satellites , vast number of asteroids , thousands of comets , and innumerable meteors , which constitute the integral part of our solar system. The nine major planets and their moon's are revolving in nearly the same plane around the sun. In addition to this movement around the sun , these planets are undergoing constant rotation about their own axis. The inner four planets , in the order of increasing distance from the sun are :-
(1) Mercury
(2) Venus
(3) Earth
(4) Mars

The outer group consists of :-
(5) Jupiter
(6) Saturn
(7) Uranus
(8) Neptune and
(9) Pluto.

The four inner planets are also known as terrestrial planets because they are about the same size , and their density suggests a composition of iron and stone. They are , thus , characterised by relatively smaller mass , much higher average density and faster speeds of rotation. These four planets have also been referred to as minor planets. The five outer planets are the major planets which reassemble the terrestrial planets , but are usually treated as a separate group. They are characterised by heavy mass , much lighter in average density , and sluggish in speeds of rotations.
Astrologers agree that all the major planets have already been discovered. The latest and the most recent discovery was that of the planets Pluto , the farthest planet from the sun , and whose position in space was predicted by astronomers more than a decade before the actual discovery in 1930. The only planet , for which no moon's are known are Mercury , Venus and Pluto. The earth has only one , whereas Saturn has ten , and Jupiter has twelve ; Mars and Neptune have two each , and Uranus has five.
Even inspite of the fact that the earth is a very insignificant component of our solar system , and much more insignificant part of our universe , it has been termed as 'remarkable' , mainly because of the fact that out of billions of celestial objects in the universe , it is the only body which is certainly known to support life , as we know it today. It also becomes of important to us because it is our home and we live on it.  It also becomes important to us because it is our home and we live on it.

-: Satellites or Moon's are those celestial bodies , each of which are revolving around any of these nine planets.

-: Asteroids are the minor planets , generally situated between the orbits of Mars and Jupiter. The largest of these bodies probably exceeds 700 km in diameter , and the smallest visible Ones are 2 to 3 km across.

-: Comets are the heavenly bodies having a long tail pointing approximately away from the sun , and a brighter head section that contains a small bright nucleus.

-: Meteors are smaller solid bodies moving through the space , and getting illuminated while entering earth atmosphere.

GEOLOGY - Around Us

If we start thinking in terms of geology , we will always find geology around us. Whether we are walking through the fields ; or driving through the country ; or standing near a temple or a building ; or sitting at a place , we will always be incontact with the processes and materials of geology. For example , pick up a piece of Limestone rock. There will probably be fossils in it , which may well represent the remains of the animals that lived in some prehistoric sea , which once covered the area.
Similarly , say for example , we are walking along a river bank , and notice the silt , which has been left on the bank by the river floods. This should , in geological parlance , remind us of the ability of the running water to deposit sediments - sediments that may on a later date be transformed into rocks. At the same place , if we notice , we can find the scoured river banks , which have been eroded by the swift water currents. This will indicate , as to how the soil has been removed by erosion - a geological process , which is so very important in shaping of various features of our Earths surface.
Sometimes , you may notice a field of black fertile soil supporting a fine crop of corn. You may be surprised to know that this dark rich soil may have been derived from an underlying chalky white Limestone - still another reminder of the importance of Earths material in our every day life.
Sometimes , you may be sitting or standing a near a building or a temple , where you will notice a various types of stones used in flooring ; or in face work ; or in a structural members. Will you not like to know as to what are rocks are they , where are they found , and what are their strengths and costs ? All these details shall indeed be provided by the study of geology.
Geology , therefore , concerns with our daily life , and is the most interesting and useful subject for a layman as well as for knowledgeable people like you. One must know , if not in a specialised manner , then atleast in a general way , something about geology. The engineers , particularly the civil engineers - who have to use the rocks for construction purposes , and the grounds (soil and rocks) for supporting their engineering structures like dam's , roads , bridges , railway tracks , docks and harbours , tunnels , etc. must have a good and a through knowledge of the subject. Similarly , the mining engineers , who have to mine the rocks , to take out ores and other rocks for their various economic and building uses , must be well aware of this subject.

GEOLOGY - Scope of Geology

The scope of geology is so broad that it has been split into two major division : (1) Physical Geology. (2) Historical Geology. Each of these divisions , have for convenience of specialised study , been further sub-divided into various branches or sub sciences. The term Earth science is commonly used in conjunction with the study of the Earth ; although Earth science includes the study of geology , and also encompasses the science of meteorology (the study of the atmosphere), oceanography (the study of oceans), and astronomy of course.

<b>1. Physical Geology :-</b> Physical geology deals with the Earth's composition , structure , the movement with in and upon the Earth's crust , and the geologic processes by which the Earth's surface is, or has been changed. This division of geology includes in itself , the following branches :-

(A) Mineralogy :- The mineralogy , obviously deals with the study of minerals. Minerals are the basic constituents of rocks , and thus , influence the properties of the rocks. Hence , in order to know the properties of the rocks , one has to study the properties of the minerals. In mineralogy , therefore ,  the mode of formation , composition , occurrence , types , association , properties , uses etc. of the minerals , shall be studied in details. This study will helps the civil engineers to know as to why the rocks like Quartzite and Marble , which though resemble in shine , colour and appearance , yet differ widely in their behavior ; Quartzites being very tough , strong and durable ; while Marbles disintegrate and decompose in a shorter period. This happens so , because of the difference in their mineral composition.

(B) Petrology :- The term Petrology is derived from the Greek word , Petro + logos. Petro means rocks and logos means study. Hence , petrology means the study of the rocks. Since the earth crust, also called lithosphere , is composed of different types of rocks , their study is under this branch , which deals with the study of mode of formation , structure , textures , composition , occurrence , types etc. of the various rocks of the Earth's crust.

(C) Structural Geology :- The rocks which constitute the Earths crust , have undergone and continuous to under go various deformations , dislocations under the influence of tectonic forces ; causing formation of geological structures like folds , faults , joints , unconfirmities etc. in the dark masses .

(D) Geomorphology :- This branch of geology explains and studies the origin of various surface features of the Earth.

(E) Economic Geology :- This is a specialised division of Mineralogy and Petrology , where in the product of the Earths crust having good economic value , are studied. Valuable ores , containing metals, like diamond , gold etc. economical minerals are like coal , petroleum , etc. do come under the domain of this specialised study. It includes the study of their occurrence , search and exploitation for commercial and industrial uses.

<b>2. Historical Geology :-</b> Historical geology deals with the study of origin and evolution of the earth and it's inhabitants. Like physical geology , this division of geology has also been bifurcated into several branches , due to the variety and vastness of this field. Each of these branches is actually a science in its own right , and one may devote a lifetime to study the specialised subject in any one of them. The various sub-division of this branch of geology includes :

(A) Stratigraphy :- These studies help in working out the geologic history of an area , and is concerned with the origin , composition , proper sequence , and correlation of the rock strata. The term Stratigraphy has been derived from the Greek words : strata + graphy. Strata means the sets or beds of sedimentary rocks ; while graphy means the description. Hence , this branch of science deals with the study of the beds of the sedimentary rocks. The study of such rocks gives an indication of the time that has passed since their formation ; thereby indicating the life history of the rocks and of the earth and it's inhabitants. The study of these rocks will also involved extraction of fossils , I.e the remains of plants and animals of the past geological Eras.

(B) Palalentology :- Palalentology deals with the study of the ancient organism , plants and animals etc. as revealed from there remains and remnants. This study helps in providing a background to the development of life on Earth , over the past geological eras.

(C) Palaeogeography :- This branch of science deals with the study of the geographic conditions of the past times. It, thus deals with the reconstruction of the relations of the ancient lands and seas , and the organism that inhabitanted them.

These branches of historical geology are , intact interconnected with each other , and overlap also in various respects ; as in the case with the various branches of physical geology.

GEOLOGY - An Introduction

We live on a wonderful planet, called the Earth , yet how little most of us really know about its composition and history. We consume the products of soil which have been formed by the weathered rocks ; we use coal, natural gas and oil formed from the remains of pre-historic plants and animals ; we enjoy the beauty of precious stones. But these are only a fraction of the valuable materials, which have been bestowed on us, by the Earth. Think of the importance of the Earths products in the development of modern industries. Our vast mineral resources , such as lead , iron , coal and petroleum are derived from the earth, and these basic products have been made available to us easily , by the application of science , which deals in the study of the Earth. This science , which deals with the study of the Earth , is known as Geology. The term "Geology" has been derived from the Greek words Geo + logos. Geo means earth , and logos means discourse or study or science. The subject of "Geology" , therefore, deals with the study of the wonderful planet 'Earth' , on which we are living. The science of Geology tell us about the origin , structure and history of the Earth and its inhabitants , as recorded in the rocks. Without its study , one remains ignorant about the same planet on which one is living.
The Earth has not only provided us with the minerals and other products , which are used and consumed by us ; but has also provided us with so many scenic things, which we call as the products of 'nature' or 'God'. The areas of exceptional beauty , like the great mountains , the deep awesome gorges , the fascinating lakes , the charming springs , the marvellous coral reefs , the spectacular volcanoes , the stupendous water falls , and what not. Even the man itself is a product of Earth and its surrounding environment. All these and many more things are the results of geological processes that are still at work within and on the Earth , even today. They are the same processes which began to shape the earth soon after its birth some four or five billion years ago.
The event of July 1969 took Geology out of its originalsphere , and plunged it into space Age : man had set foot on the moon and brought back samples of moon rocks for the geologist - the Earth scientist , to study. Who knows to what such studies will lead ? Shall we have a clearer picture of the origin of both moon and Earth ? Shall we find on the moon , rich mineral deposits, or minerals as yet unknown to us.
Perhaps , we will be visiting other planets with in our solar system in the coming years ; this too , will create fascinating new branches of geology.
But now , let us return to our own planet. To a geologist , the earth is not a simple globe , upon which we live ; it is an ever - present challenge to learn more about such things as earthquakes , volcanoes , glaciers and the meaning of fossils. How old is the earth ? Where did it come from ? Of what is it made of ? What will happen to it in future ? To answer such questions , the Earth scientists (geologist) must study the evidence of events that occurred millions of years ago. He must then relate his findings to the results of similar events that are happening today. He tries , for example , to determine the location and extent of ancient oceans and mountains , and to trace the evolution of life as recorded in the rocks of different ages. He studies the composition of rocks and minerals forming the crust of the Earth , in an attempt to locate and exploit the valuable economic products that are to be found there. In perusing his study , a geologist heavily relies upon other basic science such as astronomy , chemistry , physics , biology , zoology , botany etc. For example , astronomy , which deals with the study of the nature and movements of planets , stars and other heavenly bodies , tells him as to where the earth fits into the universe , and has also suggested several theories as to the origin of our planet. Chemistry , for example , deals with the study of the composition of substances and changes which they undergo , helps a geologist in analysing and studying the rocks and minerals of the Earths crust. The science of physics , which deals with the study of matter and motion , again helps a geologist to interpret and explain the various physical forces affecting our Earth , and the reactions of the Earths material to these forces.
Similarly , to understand and interpret the per-historic plants and animals , a geologist takes the help of biology , which deals with the all living forms. Similarly , Zoology provides him detailed information about the animals ; and botany gives insight into the nature of ancient plants. By using all these sciences as well as others , a geologist is better able to cope with the many complex problems that arise in the study of the Earth and it's history.