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the origin and evolution of the earth

Origin of the earth
  • Early theories:
    • Nebular Hypothesis
    • Binary Theory
  • Modern Theory:
    • Big bang theory.

Nebular hypothesis theory:
It is given by General philosophy Immanuel Kant. In 1796, mathematics Laplace revised this theory.
As per nebular hypothesis theory:

  • Sun was surrounded by a solar nebula comprised of mostly hydrogen and helium along with dust. Friction and collision of particles lead to the formation of a disk-shaped cloud. Through the process of accretion, planets were formed out of material associated with the youthful sun.
  • Nebular hypothesis theory does not explain the sources of origin of the nebula.
  • It was not able to explain the sources of heat and motion of the nebula.
  • As per the nebula hypothesis, the nebula is in the gaseous state so the planet should also be in gaseous form, but the same is not true. The theory is not able to explain house gases nebula leading to the formation of solid planets.
  • All the planets and satellites should rotate in the same direction as the nebula rotates but the same is not true.
Binary theory or Planetesimal Hypothesis:
In 1900, Chamberlain and Moulton gave the binary theory.
As per theory:
  • Another wondering star approached the sun. As a result, the cigar-shaped extension of the material was separated from the solar surface.
  • As the passing star moved away, separated material slowly condensed into a planet and continued to revolve sun.

Modern theory:
Early theories only focus on the evolution of the earth and the planet, but modern theory tries to solve the problems of the origin of the universe.
Big bang theory:
It is also called the expanding universe hypothesis.
In 1920, Edwin Hubble provides evidence that the universe is expanding.
Over time, the distance between Galaxies is increasing.
As per big bang theory:
  • All matter that formed the universe existed in one place having less than the area of the atom with unimaginable small volume, infinite temperature, and infinite density.
  • It exploded with a big bang around 13.7 billion years ago.
  • Within 3 minutes of the big bang event, the first atom was formed.
  • Over time, the energy was converted into matter.
  • After the formation of atomic matters, around 3 lakh years from the big bang, the universe becomes transparent.
Star formation as per big bang theory:
  • It starts 5 billion years ago.
  • In the early universe, the distribution of matter and energy was not even. Due to the initial density difference, it gets rises to gravitational forces. As a result, the matter came together.
  • The universe is a collection of large numbers of galaxies.
  • Galaxy: contains a large number of stars.
  • The formation of galaxies started from the nebula which is made up of hydrogen and helium gases.
Formation of planets:
The following are stages in the development of planets:
First stage:

  • The star is a lump of gas within the nebula. The gravitational force within lumps leads to the formation of the core and the huge rotating discs of gases and dust around the gaseous core.
Second stage:
  • The matters around the core, get condensed into smaller rounded objects. Planetesimals are a large number of smaller bodies and by collision, larger bodies start forming.
Final stage:
  • These planetesimals form and form larger planet bodies.

Our solar system:
Our solar system formed 5 billion years ago. The solar system is comprised of nine planets, many satellites, asteroids, and one sun.
Nine planets are in two types:
  • Inner planet or terrestrial or Earth-like planet:
    • These are Mercury, Venus, Earth, Mars
  • Outer planet or Julian or giant planets:
    • These are Jupiter, Saturn, Uranus,  Neptune, and Pluto.
Jovian planet is larger in size as compared to the terrestrial planet and has a thick atmosphere mostly made of helium and hydrogen.
Difference between Julian and Terrestrial planets:
  • Terrestrial planets are formed by solid particles whereas Julian is formed by gaseous particles.
  • Solar winds blew off lots of gases and dust from terrestrial planets where similar removal has not happened on Jovian planets.
  • A terrestrial planet is smaller hence lower gravity could not hold the escaping gases.
Evolution of earth:
  • Initially, the earth was a barren, rocky, and hot object with a thin atmosphere of hydrogen and helium.
  • Earth has a layered structure from the outmost atmosphere to the central earth. It is not uniform.
Development of lithosphere:
Due to the gradual increase in density, the temperature inside the earth is increasing. As a result, materials get separated depending on their density. Iron sink towards the center and lighter one move towards the surface.
During the formation of the moon, the earth was further heated up. Further, in the process of differential, three major layers are made on earth.
These three layers are:

  • Crust
  • Mantle
  • Core
Evolution of atmosphere and hydrosphere:
The present atmosphere is made by three stages:
First stages:
  • Loss of primordial atmospheres such as helium and hydrogen blew off by solar winds.
Second stage:
  • The hot interior of the earth contributed to the evolution of the atmosphere. During the cooling, gases and water vapor from the interior of the earth came out into the atmosphere. At this stage, the atmosphere is largely comprised of water vapor, nitrogen, carbon dioxide, methane, ammonia, and very little free oxygen. This process is called degassing.
Third stage:
  • The composition of the atmosphere was modified by living organisms through photosynthesis and oxygen began to flood the atmosphere.
  • Carbon dioxide in the atmosphere got dissolved in rainwater and further decreased causing more condensation and more land.
Origin of life:
  • Origin of life is a kind of chemical reaction. First, it generated complex organic molecules that could duplicate themselves converting them into living substances. Life began to evolve, 3800 million years ago from blue algae.
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14 November 2021 at 09:25 ×

Laplace corrected it in 1796

2 June 2022 at 09:56 ×

Change the year of Pierre Laplace revised theory to 1796