Origin and Evolution of Earth Notes in English Class 11 Geography Chapter-2 Book-Fundamental of Physical Geography
0Team Eklavyaजून 11, 2025
Origin of the Earth
There are two important theories regarding the origin of the earth
1. Initial Principles
i. Gaseous hypothesis
Immanuel Kant
ii. Nebula hypothesis
Laplace
Otto Schmidt and Carl Weizsäcker made some modifications to the nebular hypothesis.
2. Modern theories
Big Bang theory, also known as the expanding universe hypothesis
Initial theory
Gaseous Hypothesis - Immanuel Kant (German Philosopher)
According to them, the cloud (solid) was made up of gas and dust particles
This gas cloud started colliding due to the force of gravity
Thereafter the temperature increased
The warm cloud began to spread
It is now changing from solid to gas
Then it started to spin
After this the cloud broke and became a planet
The center of the cloud (nebula) became the sun
In this hypothesis of Immanuel Kant, mathematician Laplace presented its modification in 1796, which is known as Nebular hypothesis.
Nebular hypothesis
According to this hypothesis, the planets were formed from a cloud of slowly rotating material
Big cloud in space: About 4.6 billion years ago, a huge cloud of gas and dust was floating in space. This cloud is called a nebula.
This cloud began to collapse inward because of gravity, it was being pulled together.
Rotation and flattening: As the cloud collapsed, it began to rotate faster and flatten into a disk shape.
Formation of the Sun: Most of the material from the collapsing cloud collected in the center of the disk. This center became hot and dense, forming our Sun.
Planet formation: The remaining gas and dust in the disk began to clump together and form clumps. These clumps grew larger and eventually became the planets, moons and other objects in our solar system.
Amendments to the nebular hypothesis
In 1950, Otto Schmidt of Russia and Carl Weizascar of Germany made some modifications in the Nebular hypothesis.
He believed the Sun was surrounded by a solar nebula composed mainly of hydrogen, helium, and dust.
Due to the friction and collision of these particles, a flat saucer shaped cloud was formed and the planets were formed through the accretion process.
After this, scientists tried to understand the problems related to the origin of not only the Earth or other planets but of the entire universe.
Modern theories
big bang theory
In modern times, the most accepted theory regarding the origin of the universe is the Big Bang theory.
This is also called the expanding universe hypothesis.
In 1920, Edwin Hubble gave evidence that the universe is expanding. With the passage of time, galaxies are moving away from each other.
Scientists believe that the distance between galaxies is increasing, but observations do not prove that galaxies are expanding.
So the balloon example is only partially valid.
The expansion of the universe means the distance between galaxies is expanding.
Hoyle presented its alternative in the name of 'Steady state concept'.
According to this concept, the universe has been the same at all times. However, after getting many proofs regarding the expansion of the universe, the scientific community is now in favor of the universe expansion theory.
expansion of the universe according to the big bang theory
Stage 1
About 13.7 billion years ago, the universe was at an extremely small and extremely hot point called a singularity.
In it all the matter was compressed together and the temperature and density were extremely high.
Stage 2
explosion of the big bang
This explosion started the universe expanding rapidly.
Immediately after the explosion, the expansion of the universe was very fast.
In this process some energy started transforming into matter.
In the first few seconds after the explosion, the size of the universe started increasing rapidly, but later the speed of expansion gradually decreased.
During this time, the first atoms began to form in the universe.
Stage 3
Temperature and substance formation
Three hundred thousand years after the Big Bang, the temperature of the universe dropped enough for atoms to begin to form.
At this time the universe became transparent, allowing light to travel through the universe with ease.
Creation of wires
At the beginning of the universe, energy and matter were not evenly distributed. The density of matter was different in different regions.
Due to these differences in density, the gravitational forces also became different. This caused the matter to accumulate (concentrate) in certain areas.
This gathering of matter became the basis for the formation of galaxies (groups of planets, stars, and other objects). The size of a galaxy can range from 80 thousand to 1 lakh 50 thousand light years.
Within galaxies, there are huge clouds made of hydrogen gas, which are called nebulae. Clumps of gas are formed in nebulae.
These gaseous clusters turn into dense and solid bodies over time. Stars start forming due to the contraction and heating of these bodies.
Stars were formed about 5 to 6 billion years ago.
Formation of planets
Stage 1
There is a huge gaseous and dusty cloud. It is called a nebula.
Due to the force of gravity, a central core (hot and dense region) is formed in this gaseous cloud.
A rotating disk of gas and dust forms around this core.
Stage 2
Small spheres begin to form in the gaseous disk, which are called "planetesimals". These small spheres are formed by the condensation of matter.
These small spheres collide and stick to each other. In this process, larger bodies are formed.
This process of collision and adhesion is important in the formation of planetesimals.
Stage 3
When many small planetesimals combine together to form larger bodies, these bodies gradually grow larger.
As a result: These larger bodies evolve into planets.
origin of the earth
The Earth was initially a hot, rocky and desolate planet.
Its atmosphere was very thin and was composed of hydrogen and helium.
Over time, events and processes occurred on Earth that changed its atmosphere and surface.
Today's Earth has a lot of water and a favorable environment for life.
Its structure is layered, consisting of different layers.
Evolution of the lithosphere
Planets are formed by the coming together of planetesimals.
As the matter was compacting due to gravity, those accumulating bodies affected the matter.
This generated a lot of heat. This process continued and the material started melting due to the heat generated.
This happened during the origin of the Earth and immediately after its origin.
Due to extreme heat, the Earth remained partially in liquid state
Due to high temperature, the mixture of light and heavy density substances started separating due to difference in density.
Due to this separation, heavier substances (like iron) moved towards the centre of the Earth and lighter substances came towards the surface or upper part of the Earth.
With time it cooled further and transformed into solid form.
Differentiation
When many small planetesimals combine together to form larger bodies, these bodies gradually grow larger.
This process of separation of substances of lighter and heavier density is called differentiation.
Evolution of the atmosphere and hydrosphere
Nitrogen and oxygen play a major role in the current composition of Earth's atmosphere.
There are three stages in the evolution of the present atmosphere.
Stage 1
Hydrogen and helium moved away from the earth due to solar wind.
Stage 2
During the cooling and differentiation of the Earth, many gases and water vapor came out from inside the Earth, which led to the formation of today's atmosphere.
Stage 3
There were continuous volcanic eruptions on the earth due to which vapors and gases were increasing.
This water vapour condensed and turned into rain, due to which oceans were formed on the earth and life developed in them.
The oceans present on Earth were formed approximately 500 million years from the origin of the Earth.
The process of photosynthesis evolved approximately 250 to 300 million years ago.
For a long time, life was limited to the oceans only.
The increase in oxygen through the process of photosynthesis is a gift from the oceans.
Origin of life on earth
The last phase of the origin of the Earth is related to the origin and development of life.
The Earth's early atmosphere was not conducive to the development of life.
Modern scientists explain the origin of life as a type of chemical reaction in which the first complex organic molecules were formed and grouped.
This group was such that it was capable of recreating itself and transforming inanimate matter into living elements.
