1. Introduction: Why do we study Origin of the Earth?
Early humans observed stars, galaxies, Earth, rivers, mountains, etc.
This curiosity led to questions like:
How was Earth formed?
Where did the Sun, Moon, and planets come from?
How did atmosphere and life originate?
With the growth of scientific temperament (Renaissance period), geographers and scientists proposed various theories.
2. Classification of Theories of Origin of the Earth
Theories are broadly divided into two categories:
A. Early Theories (Hypotheses)
Based on assumptions
No proper scientific proof
Also called Hypothetical theories
B. Modern Theory
Supported by scientific evidence
Most accepted theory today
3. Early Theories (Hypotheses)
Major Early Theories mentioned in NCERT:
Gaseous Theory of Kant
Nebular Hypothesis of Laplace
Planetesimal Theory
Tidal Hypothesis
Revised Nebular Hypothesis (Otto Schmidt)
4. Gaseous Theory of Kant (Immanuel Kant)
Basic Information
Proposed by Immanuel Kant
Around 1750
Influenced by Newton’s Law of Gravitation
Newton’s Law (Background)
Every object with mass attracts every other object.
Greater the mass → stronger the gravitational force.
Lesser the distance → stronger the attraction.
5. Assumptions of Kant’s Gaseous Theory
Kant made some basic assumptions (without proof):
Assumption 1: Primordial Gaseous Cloud
In the beginning, the universe had a huge primordial cloud made of:
Gas
Dust
This cloud was:
Cold
Solid in nature
Motionless
Assumption 2: Presence of Gravity
Dust and gas particles had mass
Due to mass, they exerted gravitational attraction
Particles started pulling each other
Assumption 3: Collision of Particles
Due to gravitational attraction:
Particles collided with each other
These collisions caused:
Friction
Heat generation
Assumption 4: Rise in Temperature
Continuous collision → increase in temperature
The cloud started becoming hot
Assumption 5: Expansion of the Cloud
When temperature increases:
Matter expands
Therefore, the gaseous cloud began to expand
6. Summary of Kant’s Gaseous Theory (Point-wise)
Universe began with a cold, motionless gaseous cloud
Dust particles had gravitational force
Mutual attraction caused collisions
Collisions produced heat
Temperature increased
Cloud expanded and started evolving
This process eventually led to formation of celestial bodies (as assumed)
7. Limitations of Kant’s Theory
Purely assumption-based
No mathematical or observational proof
Could not explain:
Exact formation of planets
Orbital motion properly
Hence, criticized by later scientists
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