EVOLUTION OF EARTH & PHYSIOGRAPHY OF INDIA [ NCERT ]

EVOLUTION OF EARTH & PHYSIOGRAPHY OF INDIA

The earth has a long geological history, and the present landforms have evolved over millions of years due to continuous action of endogenic and exogenic forces. The earth is estimated to be about 460 million years old, and throughout this time, internal movements and external processes have shaped both surface and subsurface features.A significant aspect of this evolution is the movement of tectonic plates. The Indian Plate, which was once located south of the equator, was originally part of a larger landmass that also included the Australian Plate. Over time, this landmass broke apart, with the Indian Plate moving northward and the Australian Plate moving southeastward. This northward movement is still continuing, and it has played a crucial role in shaping the physical environment of the Indian subcontinent.

GEOLOGICAL DIVISIONS OF INDIA

Based on geological structure and formation, India can be divided into three major regions:

• The Peninsular Block
• The Himalayas and other Peninsular Mountains
• Indo-Ganga-Brahmaputra Plain

These divisions broadly correspond to the major physical features of India.

THE PENINSULAR BLOCK

The Peninsular Block is a stable and ancient landmass, formed primarily of gneisses and granites. It has remained rigid since the Cambrian period, except for minor changes due to tectonic activity.

Extent & Structure

• Northern boundary: From Kachchh → Aravali near Delhi → parallel to Yamuna & Ganga → Rajmahal Hills → Ganga delta
• Extensions: Karbi Anglong and Meghalaya Plateau (NE), Rajasthan (West)
• Separated from Chotanagpur Plateau by Malda Fault

Geological Characteristics

• Part of the Indo-Australian Plate
• Subjected to vertical movements and block faulting
• Formation of rift valleys:
  • Narmada, Tapi, Mahanadi
• Presence of block mountains: Satpura

Relief Features

• Dominated by relict and residual mountains:
  Aravali, Nallamala, Javadi, Veliconda, Palkonda, Mahendragiri
• Shallow river valleys with low gradients

Drainage

• East-flowing rivers form deltas:
  Mahanadi, Godavari, Krishna, Kaveri

HIMALAYAS AND OTHER PENINSULAR MOUNTAINS

The Himalayas are young, weak, and flexible mountains, unlike the stable Peninsular Block.

Key Characteristics

• Tectonic origin
• Subject to continuous endogenic and exogenic forces
• Formation of faults, folds, thrusts
• Rivers are youthful and fast-flowing

Associated Landforms

• Gorges
• V-shaped valleys
• Rapids and waterfalls

These features indicate an early stage of geomorphic development.

INDO-GANGA-BRAHMAPUTRA PLAIN

This plain represents a geo-synclinal depression, which developed during the third phase of Himalayan formation (~64 million years ago).

Formation

• Gradually filled by sediments brought by rivers
• Deposits from both Himalayan and Peninsular rivers

Characteristics

• Alluvial deposits depth: 1000–2000 m
• Extremely fertile and level plain
• Strong influence on physiography and human settlement

PHYSIOGRAPHY OF INDIA

Physiography refers to the combined effect of structure, processes, and stage of development. India exhibits great diversity in physical features:

• North: Rugged mountains, deep valleys
• South: Stable plateau, dissected relief
• Middle: Vast plains

Major Physiographic Divisions

1. Northern and North-eastern Mountains
2. Northern Plains
3. Peninsular Plateau
4. Indian Desert
5. Coastal Plains
6. Islands

NORTHERN AND NORTH-EASTERN MOUNTAINS

This region includes the Himalayas and Northeastern hills, forming a series of parallel ranges.

Orientation

• NW India: Northwest → Southeast
• Darjeeling–Sikkim: East–West
• Arunachal Pradesh: Southwest → Northwest
• Nagaland–Manipur–Mizoram: North–South

Dimensions

• Length: ~2500 km
• Width: 160–400 km

Significance

• Acts as a physical, climatic, drainage, and cultural barrier
• Separates Indian subcontinent from Central & East Asia

NORTHERN PLAINS

Formed by alluvial deposits of Indus, Ganga, Brahmaputra rivers.

Extent

• Length: ~3200 km
• Width: 150–300 km

Subdivisions

Landforms

• Meanders, oxbow lakes, braided channels, sand bars
• Frequent floods and shifting river courses

Special Features

• Sunderbans delta – one of the largest
• Fertile soil → supports dense population and agriculture

PENINSULAR PLATEAU

An irregular triangular plateau, rising from 150 m to 900 m.

Boundaries

• Delhi Ridge, Rajmahal Hills, Gir Range, Cardamom Hills
• Extensions: Shillong & Karbi Anglong Plateau

Characteristics

• Oldest and most stable landmass
• Composed of series of plateaus:
  Malwa, Ranchi, Hazaribagh, Karnataka, Coimbatore

Relief Features

• Tors, block mountains, rift valleys, spurs, hummocky hills
• Quartzite dykes (natural water storage sites)
• Black soil region (NW part)

Divisions

• Deccan Plateau
• Central Highlands
• Northeastern Plateau

(A) Deccan Plateau

• Bounded by Western Ghats, Eastern Ghats, Satpura range
• Western Ghats: Higher, continuous (~1500 m)
• Eastern Ghats: Lower, discontinuous
• Highest peak: Anaimudi (2695 m)
• Rivers originate mainly from Western Ghats

(B) Central Highlands

• Bounded by Aravali (west) and Satpura (south)
• Elevation: 700–1000 m
• Contains Vindhyan and Kaimur ranges
• Features:
  • Relict mountains
  • Metamorphic rocks (marble, slate, gneiss)
  • Ravines of Chambal, Bhind, Morena

(C) Northeastern Plateau

• Extension of Peninsular Plateau
• Separated by fault (Rajmahal–Meghalaya)
• Divisions:
  • Garo Hills
  • Khasi Hills
  • Jaintia Hills
• Rich in minerals and receives heavy rainfall
• Highly eroded surface

THE INDIAN DESERT

Located northwest of Aravali, known as Marusthali.

Features

• Low rainfall (<150 mm)
• Sand dunes (barchans), mushroom rocks, oasis
• Evidence of marine origin (Mesozoic era)

Drainage

• Mostly ephemeral rivers
• Luni River is significant
• Presence of inland drainage and playas (salt lakes)

COASTAL PLAINS

India’s coastline is divided into:

(A) Western Coastal Plains

• Submerged coast, narrow belt
• Ideal for ports and harbours
• Divisions:
  • Kachchh & Kathiawar
  • Konkan
  • Goa coast
  • Malabar coast
• Special feature: Kayals (backwaters)

(B) Eastern Coastal Plains

• Emergent coast, broader
• Formation of large deltas:
  Mahanadi, Godavari, Krishna, Kaveri
• Fewer ports due to wide continental shelf

ISLANDS OF INDIA

Bay of Bengal Islands (Andaman & Nicobar)

• ~572 islands
• Divided into Andaman (north) & Nicobar (south)
• Separated by Ten Degree Channel
• Features:
  • Volcanic origin (Barren Island – active volcano)
  • Peaks: Saddle Peak, Mount Diavolo, Mount Koyob, Mount Thuiller
  • Equatorial vegetation, heavy rainfall

Arabian Sea Islands (Lakshadweep)

• 36 coral islands
• Located off Kerala coast (280–480 km)
• Divided into Amini & Cannanore groups
• Features:
  • Coral origin
  • Storm beaches
  • Limited habitation (11 islands)

FINAL REVISION LINES

• Indian Plate → northward movement → major geological impact
• Peninsular Block → oldest, stable, faulted region
• Himalayas → young, tectonic, dynamic mountains
• Northern Plains → fertile alluvial deposits
• Plateau → oldest landmass with diverse relief
• Desert → arid, wind-shaped landforms
• Coastal Plains → submerged west vs emergent east
• Islands → coral (Lakshadweep) vs volcanic (Andaman & Nicobar)