The three major landforms of the Earth are:
1. **Mountains:** These are natural elevations of the Earth's surface, characterized by high altitude, steep slopes, and often a pointed peak or summit. They are formed through various geological processes like folding, faulting, and volcanic activity. Examples include the Himalayas and the Alps.
2. **Plateaus:** These are elevated flat-topped tablelands that rise abruptly from the surrounding land. They have a more or less flat surface on top and often steep sides. Plateaus are often rich in mineral deposits. Examples include the Deccan Plateau and the Tibetan Plateau.
3. **Plains:** These are large stretches of flat or gently rolling low-lying land. They are generally very fertile, making them ideal for agriculture and human settlement. Plains are formed by the deposition of sediments by rivers. Examples include the Ganga Plain and the Mississippi Plain.

Plains are densely populated for several reasons:
1. **Fertile Soil:** Plains, especially river plains, have very fertile soil deposited by rivers, which is excellent for agriculture. This allows for high food production to support a large population.
2. **Easy Transportation:** The flat terrain of plains makes it easy to build roads, railways, and canals, facilitating transportation and communication.
3. **Ease of Construction:** It is easier and less expensive to construct houses, factories, and other infrastructure on flat land compared to mountainous or hilly regions.
4. **Availability of Water:** Many plains are formed by rivers, ensuring a good supply of water for drinking, irrigation, and other domestic and industrial uses.
5. **Favourable Climate:** Many plains have a moderate climate suitable for human habitation and various economic activities.

The primary economic activity on plateaus is **mining**. This is because plateaus are often rich in mineral deposits such as iron, coal, gold, and diamonds. The geological processes that form plateaus, particularly volcanic activity (in the case of lava plateaus), often bring these valuable minerals closer to the Earth's surface, making them accessible for extraction. The Chhota Nagpur Plateau in India, for example, is famous for its vast mineral wealth and associated mining industries.

The main difference between 'young fold mountains' and 'old mountains' lies in their geological age, formation, and appearance:
1. **Young Fold Mountains:** These are mountain ranges that were formed relatively recently in Earth's geological history (tens of millions of years ago). They are still undergoing geological processes and are often characterized by rugged relief, high peaks, and steep slopes. They are formed when two tectonic plates collide, causing the Earth's crust to fold and uplift. **Example:** The Himalayas, the Alps, and the Andes.
2. **Old Mountains:** These are mountain ranges that are much older (hundreds of millions of years ago) and have been subjected to significant erosion over long periods. As a result, they are generally lower in height, have rounded peaks, and gentler slopes. They may have once been very high but have been worn down by wind, water, and ice. **Example:** The Aravalli Range in India, the Appalachians in North America, and the Ural Mountains in Russia.

Life is difficult in mountainous areas due to several challenging conditions:
1. **Harsh Climate:** Mountains often experience extreme weather conditions, including very cold temperatures, heavy snowfall, and strong winds, making survival challenging.
2. **Steep Terrain:** The steep slopes and rugged terrain make it difficult to build houses, roads, and other infrastructure. Movement and transportation are also arduous.
3. **Limited Arable Land:** There is very little flat land suitable for large-scale agriculture. Farming often requires specialized techniques like terrace farming.
4. **Natural Hazards:** Mountainous regions are prone to natural disasters such as landslides, avalanches, and flash floods, which pose a constant threat to life and property.
5. **Sparse Resources:** Access to essential services like healthcare, education, and markets can be limited due to the remote and inaccessible nature of many mountain regions.

The Ganga Plain is the most densely populated area of India primarily due to its highly favorable conditions for human settlement and economic activities:
1. **Extremely Fertile Soil:** The plain is formed by the deposition of fertile alluvial soil by the Ganga River and its tributaries, making it ideal for intensive agriculture. This supports a large population with abundant food.
2. **Abundant Water Supply:** The presence of the Ganga River and numerous tributaries ensures a perennial supply of water for drinking, irrigation, and industrial use.
3. **Flat Terrain:** The flat and gentle slopes of the plain make it easy to construct infrastructure like roads, railways, canals, and buildings, facilitating connectivity and development.
4. **Favourable Climate:** The climate is generally moderate, supporting a wide range of crops and comfortable living conditions for most of the year.
5. **Historical Significance:** The region has been a cradle of ancient civilizations and has a long history of human settlement, leading to the development of major cities and cultural centers.

The **plateau** is a flat-topped tableland.

The Himalayas are an example of **young fold** mountains.

The **Mount Everest** is the highest mountain peak in the world.

The Gobi Desert is an example of a **cold** desert.