Class 9 Geography

Tectonic Plate Theory

This part is not in your textbook, but it is important to udnerstand how the continents were formed. You will find it interesting to know how the Indian Peninsula drifted from the Gondwana Land and finally hit the Eurasian plate to form the mighty Himalayas. This also helped in forming the north Indian plains, the cradle of human civilization since ancient times.

The tectonic plate theory describes the large scale motion of the earth’s lithosphere. This theory is based on continental drift which explains the formation of various continents over millions of years; as we see them today.

convergent boundary divergent boundary transform boundary

Plate Boundaries:

Based on the relative movement between two tectonic plates, there are three types of plate boundaries. They are as follows:

  1. Convergent Boundary: In this case, the two adjacent tectonic plates move towards each other.
  2. Divergent Boundary: In this case, the two adjacent plates move away from each other.
  3. Transform Boundary: In this case, the two adjacent plates move along their borders.

About 225 million years ago, the earth contained a single landmass called Pangaea. That landmass was divided into two landmasses, viz. Laurasia and Gondwana Land about 200 million years ago. As the figures (given here) show, the landmasses further broke into different parts and experienced continental drifts at various stages. The Gondwana Land included the modern day India, Australia, North America, South America and Antarctica.

permian triassic jurassic cretaceous present period

Formation of India

The Indian Peninsula drifted towards the north and finally collided with the much larger Eurasian Plate. As a result of this collision, the sedimentary rocks which were accumulated in the geosynclines (known as Tethys) got folded and formed the mountain systems of the West Asia and Himalaya.

physical features of India

Due to the uplift of the Himalayas in the Tethys Sea, the northern flank of the Indian Peninsula got subsided and formed a large basin. That basin was filled with sediments from the rivers which came from the mountains in the north and from the peninsula in the south. Thus, an extensive flat land of alluvial soil was formed which is known as the northern plains of India.