Chapter 1.2 Formation of Continents ,Continental Drift Theory,Earthquake,Volcanoes.

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Formation of Continents:

• The Earth is about 4.5 billion years old.

• About 70% of the Earth’s surface is covered by oceans (Hydrosphere).

• The remaining 29.2% is land (Lithosphere).

• More than 75% of land area lies in the Northern Hemisphere.

  • Hence called the Land Hemisphere.

  • Southern Hemisphere is called the Water Hemisphere.

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Continental Drift Theory:

Proposed by Alfred Wegener (1924).

Main Idea:

• Around 200 million years ago, all continents were joined together as one supercontinent called Pangaea.

• It was surrounded by a large ocean called Panthalassa.

Break-up of Pangaea:

Pangaea split into two major landmasses:

1. Angaraland (Laurasia)

2. Gondwanaland

Between them formed a narrow sea called the Tethys Sea.

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Further Division:

Angaraland divided into:

• North American Plate

• Eurasian Plate

Gondwanaland divided into:

• African Plate

• South American Plate

• Indian Plate

• Australian Plate

• Antarctic Plate

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Indian Plate Movement:

• About 40 million years ago, the Indian Plate drifted north-east.

• It collided with the Eurasian Plate.

• This collision led to the formation of the Himalayas.

  Important Note:

  • If the Earth’s rotation or revolution stops, there would be:

    • No day and night

    • No seasonal changes

  • If the Earth’s axis was not tilted, there would be:

    • No seasonal variation

    • Uniform climate throughout the year

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  Earthquake:

                         
  
  

  Definition:

  An earthquake is a sudden shaking or vibration of the Earth’s crust.

  Causes:

  • According to the Plate Tectonic Theory, the Earth’s crust is divided into plates.

  • These plates move continuously over the semi-molten mantle.

  • When plates collide or move suddenly, energy is released as seismic waves.

  • Earthquakes can also be caused by volcanic activity.

  Important Terms:

  • Focus (Hypocentre): The point inside the Earth where the earthquake originates.

  • Epicentre: The point on the Earth’s surface directly above the focus.

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  Volcanoes:

  Definition:

  A volcano is an opening in the Earth’s crust through which molten material erupts.

  • Molten rock inside the Earth is called magma.

  • When it reaches the surface, it is called lava.

  • Lava contains hot gases, water vapour, ash, and small rock fragments.

  Effects of Volcanoes:

  • Can destroy property and life.

  • Can change landscapes.

  • Form mountains, islands, plateaus, and lava plains.

  • Enrich soil fertility.

  • Form geysers and hot springs.

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  Types of Volcanoes:

  1. Effusive Volcanoes:

     • Quiet eruptions with flowing lava.

  2. Explosive Volcanoes:

     • Violent eruptions with loud explosions.

  3. Active Volcanoes:

     • Currently erupting or showing signs of activity.

     • Example: Barren Island, Mount Etna

  4. Dormant Volcanoes:

     • Inactive for a long time but may erupt again.

     • Example: Mount Vesuvius, Mount Fuji

  5. Extinct Volcanoes:

     • Have permanently stopped erupting.

     • Example: Mount Kilimanjaro

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  Tsunami:

• The word “Tsunami” is Japanese and means harbour waves.

• Caused mainly by undersea earthquakes.

• The Pacific Ocean is the most tsunami-prone region.

• In October 2007, India established an advanced Tsunami Warning System at Hyderabad.

• Volcanic islands in oceans are called “Nuclei of Future Continents.”

  Disclaimer:

  This content is prepared for educational and informational purposes only. The notes are simplified for better understanding and exam preparation (UPSC and State Exams). Readers are advised to refer to standard textbooks and official sources for detailed study