Since geography is relates to studying the Earth, and the Earth is continually changing. Nothing on Earth remains in a static position. The only constant on the Earth is change. The rate of things change differs from place to place.

The geographical phenomena, both human and physical, are highly dynamic. They change gradually because of the inter-active processes between ever hanging earth and ever-active and untiring human beings. There subsist changes over the earth’s surface in its physical as well as human and cultural environs.

Many phenomena are similar and several are dissimilar. It is, thus, logical to distinguish geography as the study of a real differentiation. Therefore, geography is supposed to study those phenomena that differ over space. Geographers study the changes/variations/adaptations in the phenomena over the surface of the earth as well as study the relations with the other factors that cause these changes.

For instance, cropping patterns vary from area to area; however this variation in cropping pattern, as a phenomenon, is associated with changes in climates, soils, market demands, and ability of a farmer to invest and technological inputs available to them. Therefore, the concern of geography is to discover the causal connection between any 2 phenomena or between more than one phenomena.

Primitive human societies were directly reliant on their immediate environs. Geography, therefore, is connected with the study of Human and Nature inter-actions as a unified whole. ‘Human is an essential part of ‘nature’ and ‘nature’ has the human imprints. ‘Nature’ has impacted different facets of human life. Its imprints is seen on clothing, food, occupation, and shelter. Human beings have gradually accepted nature by way of adaptation and modification.

Physical geography looks at the natural processes of the Earth, such as climate and plate tectonics. Human geography looks at the impact and behaviour of people and how they relate to the physical world. Physical geography is the study of natural features and phenomena on the planet's surface and our interactions with them. Geography doesn't just determine whether humans can live in a certain area or not, it also determines people's lifestyles, as they adapt to the available food and climate patterns.

Biosphere reserves are the protected areas meant for the conservation of plants and animals. It also restores the traditional life of the tribals living in that vicinity. They conserve the biodiversity of that area.

There are 18 Biosphere Reserves in India established by the government that protect large areas of natural habitats. These areas are provided with the buffer zones that are open for some economic uses. Not only the flora and fauna but also the humans inhabiting these areas are protected.

The Biosphere Reserves are identified by the Man and Biosphere Reserve Program to promote sustainable development. This program was initiated by UNESCO in 1971. This program recognizes areas that:

• are the world’s most typical terrestrial and coastal ecosystems.

• areas that exhibit approaches ton live and work in harmony with nature.

• that demonstrates the achievement of a sustainable balance between conserving natural ecosystems and biodiversity.

Areal differentiation represents one of the classic philosophical approaches to geographic inquiry. A central concept of areal differentiation is that the surface of the earth may be divided into regions, which may be distinguished and categorised using various spatial criteria. Thus, areal differentiation provides the theoretical foundation for regional geography, by conceptualising space as consisting of identifiable units that may be distinguished from one another on the basis of a set of phenomena or criteria. When there is similarity and dissimilarity among the physical and cultural features on the earth surface, it is called aerial differentiation.

There were lots of hypothesis regarding the origin of life on earth. Certain experts suggested that life came from outer space as spores while another group explained that life came from a non-cellular component such as decaying matters like mud. The latter theory was known as the theory of spontaneous generation, which was discarded later.

In the year 1953, Oparin and Haldane suggested that life originated from non-living organic molecules like proteins and RNA. This was followed by the theory of chemical evolution which suggested that atmospheric conditions of earth led to the formation of organic molecules from inorganic molecules. Few scientists conducted experiments regarding the same. However, once the first life came into existence, they started to evolve in different ways and forms. This laid a stepping stone to the theory of evolution.

Humans are sophisticated and evolved animals who have modified the natural environment to make it suitable for living. While human dependency on nature has been decreased over the process of evolution, people still demonstrate many forms of nature contentedness. This includes emotional attachment to nature, perception of themselves as a part of nature, and activities aimed at nature protection. Human is an integral part of nature and nature has imprints of man.

Variations in the natural as well as cultural phenomena provides a clue in understanding the relationship

between physical environment and cultural features.

The physical environment has provided the stage over which the human societies enacted the drama of their creative skills with the tools and techniques which they invented in the process of their development. It can be said that geography is the description of the earth. We know that the reality is always multifaceted and the earth is also multi-dimensional. This is why many disciplines from natural sciences and a number of sister disciplines in social sciences study different aspect of the earth's surface. Geography is different from other subjects but at the same time it is closely related to

other disciplines. Geography derives its data base from all the natural and social sciences.

The existing variations over the surface of the earth in physical as well as cultural environment. A number of phenomena are similar and many are dissimilar. It is, therefore, logical to perceive geography as the study of a real differentiation.

 Riverine means anything that is related to rivers. Islands which gets formed in the river when the water level drops down is called riverine islands. These types of islands are also created when two rivers interconnect with each other.

The remaining land in between is called the riverine island. Many isles formed in Bangladesh by Brahmaputra are some of the examples of riverine islands.

There are two sources for information about interior of the earth – a) Direct Sources and b) Indirect Sources:

• Direct Sources: Mining, drilling and volcanic eruption are examples of direct sources. During the process of mining and drilling rocks and minerals are extracted which gives information that there are layer system in the crust. Crust is made of many kinds of rocks and minerals. Volcanic eruption suggests that there is some zone inside the earth which is very hot and in liquid condition. Direct sources are not very reliable because mining and drilling can be done only up to some depth only.
• Indirect Sources: Seismic waves, gravitational field, magnetic field, falling meteors etc are example of indirect sources. They are very important for know about earth‘s interior. Movement of seismic wave suggests that there are three layers in the earth and each layer has different density. Density increases toward the center of the earth. Movement of seismic wave suggests two things: a) There are three layers in the earth and b) Each layer has different density which increases toward the center of the earth.

There are two sources for information about interior of the earth – a) Direct Sources and b) Indirect Sources:
•Direct Sources: Mining, drilling and volcanic eruption are examples of direct sources. During the process of mining and drilling rocks and minerals are extracted which gives information that there are layer system in the crust. Crust is made of many kinds of rocks and minerals. Volcanic eruption suggests that there is some zone inside the earth which is very hot and in liquid condition. Direct sources are not very reliable because mining and drilling can be done only up to some depth only.
Indirect Sources: Seismic waves, gravitational field, magnetic field, falling meteors etc are example of indirect sources. They are very important for know about earth‘s interior. Movement of seismic wave suggests that there are three layers in the earth and each layer has different density. Density increases toward the center of the earth.

The direct sources are those that provide first-hand information about events whereas the indirect sources involve the reports and analysis of direct information by other people. In scientific disciplines, experiments are the most common direct source; in other disciplines, surveys and interviews, or research into written and oral records of events provide direct access to information. Most of our information about earth's interior has come from seismic studies. Seismic waves produced during an earthquake are recorded by a seismograph when these waves reach the surface of the earth. There are two types of seismic waves- body waves and surface waves.

Four types of seismic waves| Specifications of all types of seismic waves.

• P- Waves (Primary waves)
• S- Waves (Secondary waves)
• L- Waves (Surface waves)
• Rayleigh waves.

 L waves they are dispersive so the particular speed at which they travel depends on the wave period and the near-surface geologic structure, and they also decrease in amplitude with depth. Typical speeds for Rayleigh waves are on the order of 1 to 5 km/s.

Wave is a flow or transfer of energy in the form of oscillation through a medium – space or mass. Sea waves or tides, a sound which we hear, a photon of light travelling and even the movement of small plants blown by the wind are all examples of different types of waves.  L waves they are dispersive so the particular speed at which they travel depends on the wave period and the near-surface geologic structure, and they also decrease in amplitude with depth. Typical speeds for Rayleigh waves are on the order of 1 to 5 km/s.

S waves, also called secondary waves and shear waves, are the second waves to hit the seismographs. They are transverse waves, which means that the motion is perpendicular to the direction of wave propagation. S waves can only travel through solids and scientists have been successful to map the interior of the earth by studying the routes of these waves.

P waves, or Primary waves are the first waves to hit the seismographs when an earthquake strikes. They are longitudinal waves which means that the direction of motion and propagation are the same.

Solar radiation is radiant energy emitted by the sun from a nuclear fusion reaction that creates electromagnetic energy.  About half of the radiation is in the visible short-wave part of the electromagnetic spectrum. The other half is mostly in the near-infrared part, with some in the ultraviolet part of the spectrum. Solar radiation, often called the solar resource, is a general term for the electromagnetic radiation emitted by the sun. Solar radiation can be captured and turned into useful forms of energy, such as heat and electricity, using a variety of technologies.

The land mass of India has an area of 3.28 million (3.28 lakh) square km; which comprises about 2.4% of the total geographical area of the world. India is the seventh largest country in the world.

Angular momentum is defined as: The property of any rotating object given by moment of inertia times angular velocity.
It is the property of a rotating body given by the product of the moment of inertia and the angular velocity of the rotating object. It is a vector quantity, which implies that here along with magnitude, direction is also considered.

Four main causes of an earthquake are:

Folding and Faulting: A fault is a fracture or a crack in the rock surface where already a great deal of displacement has taken place. If a fault is located in a zone, where the plates moves against each other, the chances of earthquakes occurring are more. San Andreas Fault of California is one such example.

Plate Tectonics: The lithosphere is broken into a number of plates called the lithospheric plates. When these plates collide with each other or slip past each other, their edges results in the creation of faults along the lines of weakness. Many earthquakes take place because of the movements of these plates.
Volcanoes: Most volcanic eruptions are accompanied by earthquakes. However, many active volcanoes are located far away from the plate margins.
Isostatic Disturbances: Isostatic disturbances may cause disturbance equilibrium of the earth’s crust. These disturbances may be produced by the deposition of sediments brought down by the rivers and glaciers on the ocean floor. As asthenosphere is in a semi molten state, the disturbance in the equilibrium may result in an earthquake.
Human Made Causes: Nuclear explosions, or the building of a large dams or water reservoirs near a fault zone may cause earthquakes in the region. One such example was the Koyna earthquake in Maharashtra which was caused due to the construction of the Koyna dam in 1957. 

The solar nebular hypothesis describes the formation of our solar system from a nebula cloud made from a collection of dust and gas. It is believed that the sun, planets, moons, and asteroids were formed around the same time around 4.5 billion years ago from a nebula. The nebular hypothesis is the leading theory, amongst scientists, which states that the planets were formed out of a cloud of material associated with a youthful sun, which was slowly rotating. ... It suggests that the Solar System is formed from the nebulous material. This theory is widely accepted to account for the formation of stars and planetary systems such as ours. The first version of the nebular hypothesis was proposed in 1755 by the German philosopher Immanuel Kant and modified in 1796 by Pierre Laplace.

The Big Bang Theory is the leading explanation about how the universe began. At its simplest, it says the universe as we know it started with a small singularity, then inflated over the next 13.8 billion years to the cosmos that we know today. The Big Bang is a scientific theory about how the universe started, and then made the stars and galaxies we see today. ... The universe began as a very hot, small, and dense superforce (the mix of the four fundamental forces), with no stars, atoms, form, or structure (called a "singularity"). A Belgian priest named Georges Lemaître first suggested the big bang theory in the 1920s, when he theorized that the universe began from a single primordial atom.

Dwarf planets are heavenly bodies that are too small to be considered a planet but too large to fall under smaller categories. The International Astronomical Unit defines a planet as something that obeys the following criteria:

1. To be in orbit around the Sun
2. Has enough gravity to pull its own mass into a round shape
3. Has cleared its orbit of smaller objects

Geography is sometimes considered as the mother of all sciences due to its links and influences on a range of other scientific fields including biology, mathematics, anthropology, geology, astronomy and chemistry. The exploration and discovery of new places, new ideas and new cultures is something that is fundamental to the human knowledge.