Evolution of Earth
Initially, the Earth was a hot, molten ball with no atmosphere or oceans. As it cooled down, the following stages occurred:
1. Formation of the core, mantle, and crust:
– The denser molten materials sank to form the core (mostly iron and nickel).
– The less-dense materials formed the mantle (rocky silicate layer).
– The lightest materials solidified to form the thin crust on the surface.
2. Outgassing and atmosphere formation:
– Volcanic activity released gases like water vapor, carbon dioxide, and nitrogen from the Earth’s interior.
– These gases formed the initial atmosphere, which was very different from today’s atmosphere.
3. Cooling and formation of oceans:
– As the Earth continued to cool, water vapor in the atmosphere condensed and formed the oceans.
– The earliest oceans were likely very hot and acidic.
4. Development of the modern atmosphere:
– Photosynthesis by early life forms (primitive bacteria) released oxygen into the atmosphere.
– This oxygen reacted with other gases, forming the current nitrogen-oxygen rich atmosphere.
5. Plate tectonics and continents:
– The Earth’s crust began to move and break up into plates, driven by convection currents in the mantle.
– These moving plates led to the formation of continents, mountains, and oceans as we know them today.
6. Evolution of life:
– Simple life forms emerged in the oceans around 3.8 billion years ago.
– Over billions of years, these life forms evolved into more complex organisms, eventually leading to the diverse life we see on Earth today.
Evolution of Earth Class 11 Geography Notes
The Earth is a remarkable planet that has undergone a fascinating journey of formation and evolution over billions of years. From its humble beginnings as a hot, molten sphere to the diverse and life-sustaining world we know today, the Earth has witnessed countless transformations shaped by cosmic events and geological processes.
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