From the very beginning, philosophers tried to find out about the origin of life on earth and how the universe was originated.
They tried to find the answer to the question like, how were the stars, constellations and the solar system formed?
How did the landscapes on the earth surface were created? And so on.
Many hypotheses have given about the origin of the solar system.
All these hypotheses can be kept in two categories mainly, they are given by,
1. Origin of the solar system at a very hot condition in a short period.
The hypothesis that belongs to this category are mentioned below,
A. Planetesimal hypothesis
Two planetesimal hypothesis are given at the different time.
Old planetesimal hypothesis was suggested by George Buffon in 1749 A.D.
According to this hypothesis when the hot gaseous mass of the space collided with a comet, some gas matters were thrown out from the main mass.
Different planets, satellites and other members of the solar system were formed by the condensation of the thrown materials and the remaining mass was the sun.
The formed new heavenly bodies began to revolve around the sun due to gravity.
In this way, the solar system was formed.
A new planetesimal hypothesis was suggested by T.C Chamberlin and F.R. Moulton in 1905 A.D.
According to this hypothesis, the comet was not struck with the gaseous mass but it just passed nearby it.
The gravity between them formed two Buggles on either side.
By the condensation of the materials of the bulges.
They were divided into different planets, satellites and other members of the solar system.
The remaining mass was the sun.
B. Nebular hypothesis
This hypothesis was founded by a German philosopher, Immanuel Kant in 1755 A.D.
Later it was improved by Laplace in 1796 A.D.
According to this hypothesis, in ancient times, a very huge gaseous was spinning on-axis.
Gradually, when its surface got cooled the matters of more density were collected in the form of a ring at the equator.
Then the ring was separated from the main body which formed the first planet by its condensation.
The process was repeated again and again until the entire system was formed.
C. Tidal hypothesis
This hypothesis was given by sir James jeans and sir Harold Jeffery in 1917 A.D.
The hypothesis suggests that when a comet was just passing nearby the hot gaseous mass found in space, a part of the mass was pulled out as a tail-like structure when the projected material was condensed and split into a number of pieces and different planets were formed which started to revolve around the remaining gaseous mass, which was the sun,
In this way, the solar system was originated.
2. Origin of the solar system at a cold Condition by a very slow process
A. Origin of the solar system from the milky way or dust cloud aggregation hypothesis
This hypothesis was given by a group of scientists in 1944 A.D. According to the hypothesis, due to the force od gravity dust particles and gases found in space got collected.
Gradually, As they formed big lumps if particles, the force of gravity among them increased and the surrounding materials were pulled more forcibly.
It increased the temperature when the temperature of the collected materials reached about 10^7 °C at its core, nuclear fusion started there.
It was the origin of the sun. In the same way, when the remaining materials collected together, the other members of the solar system were formed.
Even though any hypothesis mentioned above is not completely convincing, the last one i.e. dust-cloud aggregation hypothesis seems to be more convincing than others.
2. Origin of the solar system at a cooled condition by a very slow process.
Origin of life on earth
Geologists say that the origin of the earth was about 4600 million years ago.
During the origin of the earth, its surface was not suitable for the survival of living beings.
It is because the atmosphere of the earth was not like the atmosphere at present.
By the chemical evolution, the formation of first life was about 3800 million years ago in water. It was a bacterium.
The study of fossils shows that the formation of algae is about 3200 million years ago.
In this way, through the process of organic evolution, simple organisms changed into complex organisms.
Human beings are the youngest organisms on earth.
Their origin is only about two million years ago.
The major and main causes of the origin of living beings on the earth are as follows,
1. The presence of O2, Nitrogen, and CO2 in the atmosphere
2. The presence of a suitable amount of water on the globe
3. The presence of suitable temperature (variation of hot and cold) on the earth
4. The presence of minerals found in the soil
5. The presence of the ozone layer in the atmosphere that protects to penetrate harmful ultraviolet rays direct coming from the sun.
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