In this chapter, We will study the origin of the earth and Universe and the formation of stars, planet. In last, we will study our solar system, moon and geological time scale.
Origin of Universe
The big bang theory is very famous in regarding to the origin of universe. It considers the following stages in the development of the universe.
In the beginning, there was a tiny ball with an unimaginably small volume infinite temperature and infinite density.
After that tiny ball exploded violently. This lead to a huge expansion.
The Big Bang took place 13.7 billion years before the present.
Within 3,00,000 year from the big bang, temperature dropped to 4,500K and gave rise to atomic matter.
Then the universe became transparent.
The star formation
A galaxy contains a large number of stars. galaxy spread over vast distances that are measured in thousand of light years.
A galaxy stars to form by accumulation of hydrogen gas in the form of very large cloud called nebula.
Formation of planet
The following are considered as the stages in the development of planet.
The stars are localised lumps of gas within a nebula.
The gravitational force within the lumps leads to formation of a huge rotating disc of gas and dust develops around the gas core.
In the next stage, the gas cloud starts getting condensed and the matter around the core develops into small rounded objects.
In the final stage, these large number of small planetesimals accrete to form a fewer large bodies in the form of planets.
Our solar system
Planet were formed about 4.6 billion years ago while solar system formed about 5.6 billion years ago.
Our solar system consist of one sun, eight planets, 63 moons millions of smaller bodies like asteroid, comet and quantity of dust and grains and gases.
Mercury, Venus, Earth and Mars are called the inner planet which is situated between the sun and the belt of asteroids
The other 4 planet called the outer planets.
It is the only natural satellite of the earth.
In 1838, Sir George Darwin suggested that initially the earth and the moon formed a single rapidly rotating body.
It was also suggested the material forming the moon was separated from what we have present the depression occupied by the Pacific Ocean.
It is now generally believed that the formation of moon as a satelite of the earth is an outcome of “giant impact”.
A body of the size of one two-three times that of the mass collided into the earth sometime shortly after the earth was formed.
It blasted a large part of the earth into space. Disposal of plastic material then continued to orbit the earth and eventually formed into the present moon.
Origin of Earth
Nebular hypothesis is related to the theory of origin of the earth. It considered the planet were formed out of a cloud of material associated with a youthful sun, which was slowly rotating.
After some years Otto Schmidt and Carl Weizascar in Germany revised the nebular hypothesis. They considered that
The the sun was surrounded by solar nebula containing mostly the hydrogen and helium along with what may be termed as dust.
Evolution of Earth
Originally the earth was Barren, Rocky and hot object with a thin atmosphere of hydrogen and helium.
After origination of earth many physical events have been happen to evolution the life on the earth.
The earth has a layered structure. from the outermost end of the atmosphere to the centre of the earth, the material that exists is not uniform.
From the surface to deeper depths, the earth interior has different zones and each of these contains materials with different characteristic.
Evolution of Lithosphere
The the earth was mostly in a bowler during its primordial stage. due to gradual increase in density the temperature inside has increased.
As a result the material inside started getting separated depending on their densities.
higher density material goes towards the centre of the earth and lighter moves toward the surface.
With the passage of time it will further and solidified and condensed into smaller size.
This letter lead to the development of the outer surface in the form of crust.
During the formation of moon due to giant impact that the Earth was further heaten up. next by the process of differentiation that the Earth forming material got separated into different layers.
Hence from crust to core density of material increases.
Evolution of Atmosphere
During the cooling of the earth, gases and water vapour released from the interior solid earth. This started the evolution of the present atmosphere.
the early atmosphere largely contains water vapour, nitrogen, carbon dioxide methane ammonia and very little of free oxygen.
continuous volcanic eruption contributed water vapour and gases into the atmosphere.
As the earth cooled, the water vapour released started getting condensed.
the carbon dioxide in the atmosphere got dissolved in then water and the temperature further decreased causing more condensation and more rains.
The rain water falling on to the surface but collected in the depressions to give rise to oceans.
The earth’s oceans were formed within 500 million years from the formation of the earth.
Sometime around 3.8 billion years ago, life began to evolve.
Origin of life
Modern scientist refers to the origin of life as a kind of chemical reaction, which first generated complex organic molecules and assembled them. This assemblage was such that they could duplicate themselves converting inanimate matter into living substance.