Hey Dosto, In this Article we will discuss Theories of origin of earth which is second article of geomorphology course of Geography Optional UPSC, therefore first of all, you should read the first article (Universe and Solar system) later on hop on this article.
Today you’re going to learn various theories of origin of earth. First of all, you should know that all the concepts, hypotheses and theories propounded for origin of the solar system are also applicable for origin of the earth.
Let’s get started.
In this article, we will read total 8 theories of origin of universe.
- Gaseous hypothesis of Kant
- Nebular hypothesis of Laplace
- Planetesimal hypothesis of Chamberlin
- Jean and Jeffery’s tidal theory
- Russel’s binary Star Hypothesis
- Hoyle’s supernova hypothesis
- Schmidt’s interstellar hypothesis
- Big bang theory
1. Gaseous hypothesis of Kant
Nebula – It is a primordial (primitive) amorphous (without shape) mass of cloud of gas and dust.
Gaseous hypothesis of Kant was based on the sound principles of Newton’s law of gravitation and rotatory motion.
- Supernaturally created primordial hard matter was scattered in the universe.
- Nebula (Slowly rotating cloud of gas) and matter was comprised of very cold, solid, and motionless particles.
- Particles began to collide against each other under their mutual gravitational attractions.
According to Kant –
- Due to mutual gravitational attraction and collision between the particles generated random motion in the primordial matter.
- As a result, Particles will collide together and also generate friction which generate heat, with the result the temperature of the primordial matter started rising.
- With the increase in temperature, the random motion as well as the rate of collision among the particles also increased. This gave extra momentum (driving force) of the rate of rotatory motion. The rise in temperature also changed the state of primordial matter from solid to gaseous particles. Thus, the original cold and motionless cloud of matter became in due course a vast hot nebula and started rotating around its axis.
- 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).
- The nebula started spinning so rapidly that an irregular ring was separated from the middle part of 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, and 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.
- According to Kant there was a primordial matter in the universe, but, he did not explain the source of the origin of the primordial matter.
- 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.
- The collision among the particles of the primordial matter can never generates rotatory motion in it. It is an erroneous statement of mechanism.
- Kant assumption that the rotatory speed of the Nebula increased with the increase of its size was against the law of conservation of angular momentum.
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. Kant’s hypothesis plays a great role for the postulation of Nebular hypothesis by Laplace.
2. Nebular hypothesis of Laplace
Laplace (French Mathematician) propounded his theory in 1796. Laplace’s nebular hypothesis was in some way similar to Gaseous hypothesis of Kant and appears like the modified version of Kant’s hypothesis.
- He assumed that there was a huge and hot gaseous nebula in the space.
- From the very beginning huge and hot nebula was rotating on its axis.
- 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.
According to Laplace
- Since, Nebula was continuously reducing in size due to gradual loss of heat from the outer surface of the nebula through radiation.
- Thus, Reduction in the size and volume of the nebula increased the circular velocity (rotatory motion) of the nebula.
- Due to the increase in velocity, nebula started spinning at very fast speed and consequently the centrifugal force become so great that it exceeded the centripetal force.
- Consequently, Outer surface was condensed due to excessive cooling and so it could not rotate with the still cooling and contracting the central nucleus of the nebula.
- And, Thus the outer ring was separated from the remaining part of nebula.
- And this separated ring started moving around the nebula.
- Laplace further maintained that the original ring was divided in to nine rings and each ring moved away from the outer ring.
- Thus, nine planets were formed from the nine rings and the remaining central nucleus of the nebula become the Sun.
- He did not describe the source of the origin of nebula.
- He did not explain that, why did only 9 rings come out from irregular ring detached from the nebula?
- If the sun is remaining nucleus of the nebula as claimed laplace,it should have a small bulge around its middle part which would point out the probable seperation of irregular ring from the sun but there is no such bulge in the middle part of the sun.
- According to nebular hypothesis all satellites should revolve in the directon of father planets but few satellites of Saturn and Jupiter revolve in the opposite direction of their father planets.
- The nebular hypothesis is unable to explain the peculiar distribution of present day angular momentum in our solar system.
Outcome: The merit of the theory lies in the fact that it is the most acceptable explanation in explaining layered structure of earth’s interior.
3. Planetesimal hypothesis of Chamberlin (1905)
Planetesimal hypothesis of Chamberlin belongs to the dualistic concepts of the origin of the Earth.
According to Chamberlin initially there were two heavenly bodies (stars) in the universe –
- and its Companion Star or Intruding star
The behaviour and properties of proto-sun were not like other stars, It was formed of very small particles which were cold and solid.
Theory: When the intruding star came very close to the the Proto-Sun infine number of small particles were detached from outer surface of proto-sun due to massive gravitational pull exerted by the giant intruding star. This matter which is dust, gases, rock fragments eventually accrete forming planets & other celestial bodies that revolves around proto sun.
Planetesimal hypothesis not only explains the origin of the earth but also throws light on the structure of the earth, the origin of its atmosphere and continents and ocean basins.
4. Jean and Jeffery’s tidal theory
This theory is somewhat similar to Chamberlin’s theory that an intruding star ejects matter from the proto sun. Chamberlin, in his theory, had assumed the proto sun to be initially as a cold body where as the Tidal theory assumes the proto sun to be hot and incandescent.
According to Tidal theory, the matter ejected are not randomly thrown dust, gases, planetesimal.
The ejected matter was in the shape of a cigar and was called as Filament from which the planets & other celestial bodies accrete.
This theory is the best interpretation in explaining the sizes of the planets as they have arranged themselves away from the sun.
5. Russel’s binary Star Hypothesis
There is a binary star system (two stars coupled together and rotating around a fixed centre of mass).
The intruding star comes close to the binary stars & eject matter from one of the star. (It doesn’t explain what happened to the intruding star and the remainant of the star from which matter got ejected.)
The ejected matter circulates into planets and revolves around the proto sun.
This theory is convenient to explain why the composition of planets are different from the sun.
6. Hoyle’s supernova hypothesis
According to Hoyle initially there were two stars in the universe –
(1.)Primitive Sun and (2.) Companion star
The companion star was of giant size and later on became supernova due to nuclear reaction.
With the passage of time, all of the hydrogen nuclei of companion star were consumed in the process of nuclear reaction and it collapsed and violently exploded
The Violent explosion of companion star resulted in to the spread of enormous mass of dust which started revolving around the primitive sun in the form of a circular disc
The matter of this disc became building material for the formation of future of planets.
Thus, the planets of our solar system were formed due to condensation of the matter of the disc.
7. Schmidt’s interstellar hypothesis
According to this theory, the initial universe comprised of stars & randomly distributed matter filling up the space in between.
According to Schimidt, this dark matter, started to revolving around the primitive rotating sun and gradually the dark matter stars accreting & condensing & thus forming the solar system.
Though Schimidt did not explain the mode of origin of these dark matter. These dark matter were called ‘inter-stellar dusts’ by Schimidt.
This theory may be considered as explaining the processes that preceded the Nebular accretionary process of Laplace & Kant.
8. BIG BANG THEORY
Big Bang theory’s idea was first given by George Le Naitre in 1920’s & was gradually contributed by many scientists. But an important role was played by Gamenov (1970’s).
According to this theory, Everything in the universe is emerged from a point known as singularity, 15 billion year ago.
The galaxies moved apart from one another as the empty space between them expanded.
The universe expanded from a very high density & high temperature state.
There was a major cosmic explosion 13-15 bn yrs ago from which all the matter of universe was thrown out which eventually accreted to form stars, solar system and celestial bodies.
Evidence in support:
- Red Shift: As an object (light) moves away from us, its wavelength increases & shift to the Red end of the spectrum (Called Red Shift).
- CBMR: Electromagnetic Radiation which was present shortly after big bang, is now observed as background microwave radiation.