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Various scientists and philosophers have propounded from time to time their concepts, hypotheses and theories to unravel the mystery and to solve the riddle of the problems of the origin and evolution of our solar system in general and of the earth in particular but none of these could be accepted by majority of the scientific community.
Though there is no common consensus among the scientists about the origin of our solar system but it can be safely argued that all planets of our solar system are believed to have been formed by the same process.
It means that all the concepts, hypotheses and theories propounded for the origin of the solar system are also applicable for the origin of the earth.
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All the views and concepts pertaining to the origin of the earth may be divided into two groups e.g.:
(i) Religious concepts, and
(ii) Scientific concepts.
Since the religious concepts do not have any logical and scientific basis, these are discarded by modern scientific community.
For example, the view of Archbishop Usher that the earth was created at 9.00 A.M. (presumably Greenwich Mean Time?) on October 26, 4004 B.C. is merely a fantasy.
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On the basis of the number of heavenly bodies involved in the origin of the solar system and the earth the scientific concepts are further divided into three groups e.g.:
(i) Monistic concept (involving only one heavenly body,
(ii) Dualistic concept (involving two heavenly bodies) and
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(iii) Binary star concept or trihybrid concept (involving more than two heavenly bodies).
Gaseous Hypothesis of Kant:
Immanuel Kant, the German philosopher, presented his treatise entitled ‘The General Natural History and Theory of the Heaven or the Essay on the Working and Mechanical Origin of the Entire Universe on the Basis of Newtonian Laws’ in 1755. Kant claimed that his ‘gaseous hypothesis’ of the origin of the earth was based on the sound principles of Newton’s laws of gravitation and rotatory motion.
In the beginning his hypothesis acclaimed world-wide appreciation but later on it was disproved as it was based on erroneous concepts and wrong application of Newtonian laws of gravitation. Inspite of severe criticism the hypothesis was considered a great step forward in the field of cosmogony and ‘he almost reverberated the mid-18th century with his words…Give me matter and I will build a world out of it.’
Kant postulated his gaseous hypothesis of the origin of the earth on the basis of a few assumptions. He assumed that supernaturally created primordial hard matter was scattered in the universe. In fact, according to Kant there was a primeval, slowly rotating cloud of gas (now called a nebula) and matter comprised of very cold, solid and motionless particles.
In terms of modern scientific language it can be said (but not described by Kant) that the temperature of primordial matter was near about 2730C or absolute zero or O0k. This was the reason that cold matter was initially motionless (according to the molecular theory of matter). He further assumed that the particles began to collide against each other under their mutual gravitational attractions.
This mutual attraction and collision between the particles generated random motion in the primordial matter. Collision of the particles also generated friction which generated heat, with the result the temperature of the primordial matter started rising.
He further argued that the random motion of the particles also generated rotatory motion in the primordial matter. Thus, the original cold and motionless cloud of matter became in due course a vast hot nebula and started spinning (rotating) around its axis.
According to Kant with the increase in temperature, the random motion as well as the rate of collision among the particles also increased. This gave extra impetus of the rate of rotatory motion (spinning) of the primordial matter. The rise in temperature also changed the state of primordial matter from solid to gaseous particles. Thus, the initial primordial matter gradually changed in hot rotating nebula. With continuous rise in temperature and rate of rotatory motion the nebula started expanding in size.
According to Immanuel Kant as the heat increased, the size of nebula increased and as the size of nebula increased, the angular velocity or rotatory speed further increased. Due to continuous increase in the size of nebula the rotatory speed became so fast that the centrifugal force (away from the centre) exceeded the attractional or centripetal force (directed towards the centre).
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The nebula started spinning so rapidly that an irregular ring was separated from the middle part of the nebula and was ultimately thrown off due to centrifugal force. By the repetition of the same process a system of concentric rings (nine) were separated from the nebula. The residual central mass of the nebula remained as the sun.
The irregularity of the rings caused the development of the cores (knots) for the formation of the corresponding planets. In other words, all the matters of each ring were aggregated at a point to form a core or a knot which ultimately grew as a planet in due course of time. Thus, it is apparent that according to Kant the earth was formed due to aggregation of all the matter of the ring which was separated from the nebula due to centrifugal force.
By the repetition of same process rings were separated from the newly formed planets and the materials of each ring were condensed to form satellites of the concerned planets. Thus, the whole solar system comprised of the sun (residual part of the rotating nebula), nine planets and their satellites were formed.
Evaluation:
Though Immanuel Kant based his gaseous hypothesis on scientific principles (Newton’s law of gravitation) to solve the problem of the origin of the solar system and the earth but his hypothesis has been rendered baseless because it is based on several erroneous facts of science.
In fact, Kant’s hypothesis was declared dynamically unsound:
(1) It was one of the basic assumptions of Kant’s hypothesis that there was primordial matter in the universe but he never explained the source of the origin of the primordial matter.
(2) Kant did not explain the source of energy to cause random motion of the particles of the primordial matter which were cold and motionless in the initial stage. According to Newton’s first law of motion ‘a body remains at rest, or if in motion it remains in uniform motion with constant speed, unless or until an external force is applied on it.’ The particles of the primordial matter, as assumed by Kant, were at rest and no external force was applied on them, then what was the cause for the random motion among the particles of primordial matter?
(3) The collision among the particles of the primordial matter can never generate rotatory motion in it. It is an erroneous statement of mechanism.
It means that if anybody is rotating, the total amount of its angular momentum will always remain constant unless an external force is applied on the rotating body. Let us understand angular momentum. Angular momentum is the product of the mass, angular velocity and the square of the radius of the rotating body.
No one can change the mass of the rotating body, that is why it is constant. Angular momentum of any rotating body can never be changed unless an external force is applied. Thus, the above equation can also be expressed in the following manner Angular velocity α 1/radius (or size).
The second equation shows that there is an inverse relation between angular velocity or the speed of rotatory motion and the radius or the size of the rotatory body. If the radius of any rotating (spinning) nebula increases or if the nebula expands in size, the angular velocity or the velocity of the rotation of the nebula will decrease. Kant’s hypothesis envisages that ‘as the heat increased the size of the nebula (or radius of the nebula) increased and as the size of the nebula increased, the angular velocity or the rotatory speed further increased.’
This statement is erroneous as it is against the law of conservation of angular momentum. Thus, the very foundation, on which Kant’s hypothesis was based, is proved unsound and wrong. However, the importance of Kant’s hypothesis lies in the fact that it was first scientific attempt for the explanation of the origin of the earth. In fact, Kant’s hypothesis paved the way for the postulation of nebular hypothesis by Laplace.
Nebular Hypothesis of Laplace:
French mathematician Laplace propounded his ‘nebular hypothesis’ in the year 1796. He elaborated his concepts about the origin of the solar system and the earth in his book entitled ‘Exposition of the World System’. Laplace’s nebular hypothesis was in some way similar to the gaseous hypothesis of Kant.
It appears that Laplace’s hypothesis is just the modified version of Kant’s hypothesis. It may be pointed out that Laplace propounded his hypothesis without mathematical formulation.
In order to remove the aforesaid defects Laplace assumed certain axioms for the postulation of his nebular hypothesis to solve the riddle of the origin of the earth:
(1) He assumed that there was a huge and hot gaseous nebula in the space. Thus, he solved the problem of heat of the nebula through this assumption.
(2) From the very beginning huge and hot nebula was rotating (spinning) on its axis.
(3) The nebula was continuously cooling due to loss of heat from its outer surface through the process of radiation and thus it was continuously reducing in size due to contraction on cooling.
Based on aforesaid assumptions Laplace maintained that there was a hot and rotating huge gaseous nebula in the space. There was gradual loss of heat from the outer surface of the nebula through radiation due to circular motion or rotation of the nebula. Thus, gradual loss of heat resulted into the cooling of the outer surface of the nebula. Gradual cooling caused gradual contraction in the size of the nebula.
These processes e.g. gradual cooling and contraction, resulted in to continuous decrease in the size and volume of the nebula. Thus, reduction in the size and volume of the nebula increased the circular velocity (rotatory motion) of the nebula. As the size of the nebula continued to decrease, the velocity of rotatory motion continued to increase. Thus, the nebula started spinning at very fast speed and consequently the centrifugal force became so great that it exceeded the centripetal force.
When this stage was reached the materials at the equator of the nebula became weightless. Consequently, the outer layer was condensed due to excessive cooling and so it could not rotate with the still cooling and contracting central nucleus of the nebula and thus the outer ring (layer) was separated from the remaining part of the nebula.
This separated ring of material started moving around the nebula. It is to be remembered that according to Laplace only one ring of material was separated from the nebula and not nine rings as conceived by Immanuel Kant. Laplace further maintained that the original ring was divided into nine rings and each ring moved away from the other ring.
All the materials of each ring condensed at a point or knot in the form of ‘hot gaseous agglomeration’. Each such agglomeration was later on cooled and condensed to form planet. Thus, nine planets were formed from nine rings and the remaining central nucleus of the nebula became the sun. Satellites were formed from the planets due to repetition of the aforesaid processes and mechanism.
This simple hypothesis offered an explanation of the facts that (with a few exceptions among the satellites) each celestial body possesses acquired motions of rotation and evolution in one and the same sense, and that the several planetary orbits are nearly in the same plane’.
French scientist Roche suggested modification in the nebular hypothesis of Laplace during mid-19th century. He opined that nine rings were separated from the nebula itself and these rings were condensed to form nine planets.
However, the nebular hypothesis is rendered untenable on the basis of the following demerits:
(1) Laplace assumed that initially there was a hot and rotating nebula but he did not describe the source of the origin of the nebula. Where did heat and motion in that nebula come from? He did not offer any explanation.
(2) What was the reason behind the formation of certain fixed number of planets from the irregular ring? Why did only 9 rings come out from the irregular ring detached from the nebula? Why not more or less rings? He could not explain the formation of fixed number of planets (9). It is quite unreasonable to imagine the situation that all matter of one ring could condense into one incandescent gaseous mass to form one planet. According to dynamical theory the ring may break up into several parts and thus several planets may be formed due to condensation of small parts.
(3) ‘The small degree of cohesion between the particles of the nebula would make the formation of rings a continuous not an intermittent process, as the theory requires’.
(4) If the sun is the remaining nucleus of the nebula as claimed by Laplace, it should have a small bulge around its middle part (equator) which would point out the probable separation of irregular ring from the sun but there is no such bulge in the middle part of the sun.
(5) If we accept the tenet of Laplace that the planets were formed from the nebula, then the planets must have been in liquid state in their initial stage. But the planets in liquid state cannot rotate and revolve around the sun properly because the rotatory motion of different layers of the liquid is not always equal. Only the solid mass of matter has the property to perform rotatory and revolutionary motions along a near circular path without losing its original shape.
(6) According to the nebular hypothesis all the satellites should revolve in the direction of their lather- planets but contrary to this a few satellites of Saturn and Jupiter revolve in the opposite direction of their father planets.
(7) About one hundred years later from the date of the postulation of Laplace hypothesis great British physicists James Clerk Maxwell and Sir James Jeans showed that the mass in the rings was not enough to provide gravitational attraction for condensation to form individual planets.
Binary Star Hypothesis of Russell:
It may be pointed out that the hypothesis based on dualistic concept failed to explain the high amount of angular momentum of the planets of present solar system, high atomic weight of the constituent elements of the planets of inner circle and lighter atomic weight of the planets of outer circle of the solar system and the distances of different planets from the sun. In order to solve these problems the scientists tried to explain the origin of the earth and the solar system with the help of three heavenly bodies.
H.N. Russell, an American astronomer, propounded his ‘binary star hypothesis’ in the year 1937 to remove the shortcomings of tidal hypothesis of Sir James Jeans. Russell opined that there were two stars near the primitive sun in the universe. In the beginning the ‘companion star’ was revolving around the primitive sun.
Later on one giant star (the third one) named as ‘approaching star’ came near the companion star but the direction of revolution of the approaching star was opposite to that of the companion star. It was believed that the distance between two stars might have been about 48,00,000 to 64,00,000 km.
It means that the approaching star might have been at a far greater distance from the primitive sun. Thus, there would have been no effect of tidal force of the giant approaching star on the primitive sun but large amount of matter of the companion star was attracted towards the giant approaching star because of its massive tidal force (gravitational pull).
As the giant approaching star came nearer to the companion star, the gravitational and tidal force continued to increase and hence the bulge on the outer surface of the companion star started growing towards the giant approaching star. When the giant approaching star came nearest to the companion star, large amount of matter was ejected from the companion star due to maximum gravitational force exerted by the giant approaching star.
The ejected matter started revolving in the direction of the giant approaching star and thus opposite to the direction of revolution of companion star. Later on planets were formed from the ejected matter. In the beginning the planets might have been nearer to each other and thus matter might have been ejected from these planets due to their mutual attraction and thus satellites might have been ejected from these planets due to their mutual attraction and thus satellites might have been formed from these matter.
Evaluation:
Though Russell solved, to some extent, the problems of distances between the planets and the sun and angular momentum of different members of the solar system by assuming the origin of the earth with the help of two stars besides the sun and by ejecting the required matter from the companion star (and not from the sun as assumed by James Jeans) to form planets.
Supernova Hypothesis of Hoyle:
F. Hoyle, a mathematician of Cambridge University (U.K.) presented his speculative theory known as ‘supernova hypothesis’ in the year 1946. His hypothesis was based on the principles of ‘nuclear physics’ and was described in his essay entitled ‘Nature of the Universe’.
According to Hoyle initially there were two stars in the universe viz.:
(i) The primitive sun and
(ii) The companion star.
The companion star was of giant size and later on became supernova due to nuclear reaction.
It may be pointed out that energy, which is emitted by any star in the form of light, heat, etc., is generated by the process known as ‘nuclear fusion’ wherein atoms of lighter elements combine under intense heat and pressure to form atoms of heavier elements, releasing vast amount of energy. The stars generally contain hydrogen.
The hydrogen nuclei slowly and slowly combine with each other to form helium. In the process comparatively heavier element helium is formed and vast amount of energy is also released.
The same type of nuclear fusion was also going on in Hoyle’s primitive sun and the companion star but the rate of nuclear fusion was many times greater in the core of the companion star than the primitive sun. With the passage of time all of the hydrogen nuclei of the companion star were consumed in the process of nuclear reaction and it collapsed (in modern and cosmogonic language) and violently exploded.
The violent explosion of the companion star (now supernova) resulted into the spread of enormous mass of dust which started revolving around the primitive sun. Hoyle maintained that when the companion star was violently exploded, the recoil of the gigantic stellar explosion threw the nucleus of the companion star out of the gravitational field of the primitive sun.
The gaseous matter coming out due to violent explosion of the companion supernova star changed into a circular moving disc which started revolving around the primitive sun. Thus, the matter of this disc became building material for the formation of future planets.
The main constituent elements of the aforesaid building material were formed during the explosion of the companion star of supernova. It may be pointed out that the explosion of the companion star or supernova generated intense heat equivalent to 5 × 109 degree C which was sufficient enough to start the process of nuclear fusion.
The intense heat and nuclear fusion became responsible for the formation of heavy elements (e.g., helium, carbon, oxygen, silicon, nitrogen, etc.). In fact, the degree of heat and pressure decides the level of heaviness of the elements in the process.
The explosion of the supernova (companion star) generated intense heat and pressure which formed heavy elements of which our primitive earth was made. Thus, the planets of our solar system were formed due to condensation of the matter of the disc formed of the matter thrown out of the supernova due to its violent explosion.
It is, thus, obvious that the planets of our solar system were not formed from the primitive sun but were formed from the heavy elements which were formed from the matter thrown out of the supernova due to nuclear reactions and violent explosion.
Evaluation:
The ‘supernova hypothesis’ of F.Hoyle helps us in solving 3 basic problems of the origin of the earth and the solar system raised by the critics since the time of the postulation of ‘tidal hypothesis’ of James Jeans viz.:
(i) The problem of great distance between the planets and the sun,
(ii) The problem of the angular momentum of the planets, and
(iii) The problem of heavier elements of the material of the planets than the sun.
Inter-Stellar Dust Hypothesis:
Otto Schimidt, a Russian scientist, proposed his ‘Inter-Stellar Dust Hypothesis’ in 1943 to explain the complex problems of the origin and characteristics of the solar system and the earth. The most outstanding characteristic feature of this hypothesis is that the earth and the solar system have been taken to have been formed from gas and dust particles, the genesis of which has not been explained by Schimidt.
The scientific researches about the universe have given ample evidences of the presence of ‘dark matter’ in the form of gas and dust particles known as ‘gas and dust cloud’ in the universe. Though Schimidt did explain the mode of origin of these dark matter but it may be safely assumed that these gaseous clouds and dust particles might have been formed from the matter coming out of the stars and meteors.
According to the ‘interstellar dust hypothesis’ our sun during its ‘galactic revolution’ captured the dark matter of the universe. The dark matter of gaseous cloud and dust particles had their own angular momentum. The dark matter after being attracted by the sun during its ‘galactic revolution’ started revolving around the primitive rotating sun. These dark matter were called ‘interstellar dusts’ by Schimidt.
It may be pointed out that in the beginning the gaseous cloud and dust particles were not well arranged and stabilized and hence these were revolving around the sun separately. Gases being less in volume were more destabilized and less systematically arranged while the dust particles being more in amount and quantity were more stabilized and systematically arranged.
Thus, the dust particles after being combined and condensed were changed into a flat disc which started revolving around the sun.
It may be pointed out that flat disc of captured dark matter started revolving around the sun under the combined impacts of three types of motions e.g.:
(i) The rotational motion of the sun itself,
(ii) Gravitational force exerted by the sun on the disc of dark matter, and
(iii) The angular momentum of dark matter of the disc.
Thus, under the combined impact of these three types of motions each and every particle of dark matter of the universe started redistributing itself on the basis of mass, density, dimension and the existing amount of centrifugal force (generated due to the revolution of matter around the sun) tending to push the particles away from the sun and the centripetal force (generated due to gravitational pull of the sun) tending to push the particles towards the sun.
Thus, the particles having larger amount of centrifugal force were thrown out towards the margins of the rotating disc of dark matter around the sun while the particles having small amount of centrifugal force were attracted towards the band of the disc nearer to the sun.
The intense heat of the sun dispersed the gaseous particles towards the margins of the disc (except oxygen which combines with iron chemically). The intense heat also formed heavy particles which remained in the inner bands of the disc. Collision among the dust particles started the process of aggregation and accretion around the bigger particles which became the embryos of the future planets but the gas particles could not condense as they could not be organized due to their continued motion.
With the passage of time these embryos captured more and more matter and thus grew in size to become asteroids. It may be pointed out that the asteroids were still inside the disc and were revolving in the evolutionary direction of the disc. These asteroids further grew in size due to continuous accretion of nearby matter around them and thus they became planets. Some matter still remained in the disc after the formation of the planets. These matter were condensed to form satellites of the planets.
It may be pointed out that since the lighter matters were pushed towards the margins of the disc (as explained above) and heavy matters were pushed towards the inner bands of the disc, the planets formed in the inner bands of the disc were also of higher density than the planets of the outer bands of the disc.
The planets of the outer bands of the disc were of low density because they were formed by the ‘freezing out’ process of the gaseous matter, The redistribution of matter and ‘averaging of the dynamic characteristics’ of the disc resulted in the placement of the planets according to well-known Titius-Bode law of planetary distances (equation 2.5).
D = 0.4 + 0.3 x zn ………. (2.5)
Where D is the distance of planets from the sun in astronomical unit and n is a coefficient, the value of which for each planet is constant e.g. Mercury ∞ Venus o, Earth 1, Mars 2 etc.
Evaluation:
The outstanding merit of the ‘inter-stellar dust hypothesis’ of Otto Schimidt is that it solves almost all of the problems of the peculiar characteristic features of our solar system like:
(i) Near circular and similar planes of orbits of the planets;
(ii) Revolution in the equatorial plane of the sun closely matching with the orbital planes of the planets;
(iii) Placement of planets according to their size on the basis of well-founded laws;
(iv) High density planets in the outer circle of the solar system and
(v) Large and peculiar distribution of angular momentum among the planets of sloar system.