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Origin of the Earth (UPSC Geography Notes)
Overview: The Earth originated around 4.6 billion years ago from cosmic dust and gas. Over time, various scientific theories tried to explain how the solar system and our planet came into existence. Understanding these theories is essential for UPSC Geography, as they form the base of Earth's evolution and geological processes.
Table of Contents
- 1. Early Theories
- 2. Modern Theories
- 3. Formation of the Moon
- 4. Evolution of Atmosphere and Oceans
- 5. Quick Revision
- 6. UPSC Previous Year Question
1. Early Theories
A. Nebular Hypothesis (Kant and Laplace – 18th Century)
- Proposed by Immanuel Kant (1755) and Pierre Laplace (1796).
- Suggested that the solar system formed from a rotating cloud of gas and dust called a nebula.
- As it rotated, it cooled and condensed, forming the Sun and planets.
- Limitation: Could not explain why the Sun has most of the mass but very little angular momentum.
B. Tidal Hypothesis (James Jeans & Harold Jeffreys – 1919)
- A massive star passed close to the Sun.
- Due to gravitational pull, material was drawn out from the Sun.
- This material later condensed to form planets.
- Limitation: Such close encounters are extremely rare and unrealistic.
🔹 C. Binary Star Hypothesis (Russell – 1937)
- Suggested that the Sun was once part of a binary star system.
- One star exploded, and debris from it formed the planets.
- Limitation: No strong observational evidence.
2. Modern Theories
A. Big Bang Theory (Origin of Universe)
- Proposed by Georges Lemaître in the 1920s, later supported by Edwin Hubble.
- States that the universe began 13.8 billion years ago from an extremely hot and dense singularity.
- The universe expanded rapidly — this expansion continues today.
- Evidence: Redshift of galaxies and Cosmic Microwave Background Radiation (CMB).
B. Nebular Cloud (Solar Nebula) Theory
- Proposed by Otto Schmidt (1944) and refined by Carl von Weizsäcker (1950).
- Around 4.6 billion years ago, the solar nebula of gas and dust began to collapse under gravity.
- The Sun formed at the center, and the remaining material flattened into a rotating disk.
- Small solid particles called planetesimals collided and merged to form the planets, including Earth.
3. Formation of the Moon
- Giant Impact Hypothesis (Most Accepted): A Mars-sized body named Theia collided with the early Earth.
- The impact ejected debris into orbit, which later condensed to form the Moon.
- Evidence: Similar chemical composition of Earth's crust and Moon rocks.
4. Evolution of Atmosphere and Oceans
| Stage | Description |
|---|---|
| First Atmosphere | Composed mainly of Hydrogen and Helium — lost due to solar wind. |
| Second Atmosphere | Formed by volcanic eruptions — water vapor, CO₂, and nitrogen dominated. |
| Third Atmosphere (Present) | Cooling led to condensation → rainfall → oceans formed; CO₂ dissolved, and oxygen increased via photosynthesis. |
5. Quick Revision
Solar System: 4.6 billion years ago
Earth formed: From planetesimals (gas + dust)
Moon: Formed by Giant Impact Theory (Theia)
Atmosphere & Oceans: Result of volcanic gases and condensation
6. UPSC Previous Year Question
Q. Which of the following theories explains the origin of the Universe?
(a) Nebular Hypothesis
(b) Tidal Hypothesis
(c) Big Bang Theory
(d) Binary Star Hypothesis
✅ Answer: (c) Big Bang Theory
Related Keywords
UPSC Geography Notes, Origin of the Earth, Physical Geography for IAS, Solar System UPSC Notes, NCERT Geography Simplified, Formation of Moon, Earth Evolution, UPSC Preparation.
Sources: NCERT Class XI – Physical Geography, NASA, Britannica
