Subsistence crisis is an extreme situation where the basic means of livelihood are endangered.
Factors responsible for it were -
1. The population of France rose from about 23 millions in 1715 to 28 millions in 1789. This led to a rapid increase in the demand for food grains. Production of grains could not keep pace with the demand. So the price of bread which was the staple diet of the majority rose rapidly. Most worker Were employed as labourers in workshops whose owner fixed their wages. But wages did not keep pace with the rise in prices. So, the gap between the poor and rich widened.
2. Things became worse whenever drought or haul reduced the harvest. This led to subsistence crisis.

The sources used by historians in the period 700 to 1750 (the Medieval Period) were quite different from the ones used in the period of Gupta dynasty and Hashavardhana. There is definitely some continuity in the sources used by the historians of both the distinct periods. For example, for obtaining information they still relied on

• Coins
• Inscriptions
• Acrhitecture
• Textual records

The archaeological and literary sources of information help historians trace history. Archaeological sources include monuments, temples, inscriptions, coins and weapons. Literary sources include manuscripts, folk tales, poems and biographies of different rulers.
A manuscript is any document that is written by hand.
 

Merits of railways are:

(i) They make it possible to conduct multifarious activities like business, sightseeing, pilgrimage along with transportation of goods over longer distances.

(ii) They bind the economic life of the country as well as accelerate the development of industry and agriculture.

(iii) They carry heavy goods and people over long distances quickly and cheaply.
(iv) They carry them in bulk.    

Some of the important foreign travellers in the medieval period were:
a. AI-Beruni's who  wrote an account  of the rulers of Delhi Sultans
b. Minhaj-us-siraj​, who wrote greately about political events of this period.
c. Marco Polo who vistied South India giving details about the economic conditions of India.
d. Batuta, who visited during Muhamad Bin Tughlaq's reign.

• Literary sources include manuscripts, folk tales, poems and biographies of different rulers.
• A manuscript is any document that is written by hand.
• Manuscripts were collected by wealthy people, rulers, monasteries and temples. The manuscripts provide detailed information to historians but they are also difficult to use.
• Manuscripts were copied by hand in India as there was no printing press in medieval India. The nastaliq style of writing Persian and Arabic is easy to read. However the shikaste style of writing is difficult to decipher.

Types of Rocks – Rocks are broadly classified into three broad categories as the following.

• Igneous Rocks : Igneous rock is one of the three main rock types. Igneous rock is formed through the cooling and solidification of magma or lava. Igneous rock may form with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.
• Sedimentary Rocks : Sedimentary rocks are formed by the deposition and subsequent cementation of that material within bodies of water and at the surface of the earth. The process that causes various organic materials and minerals to settle in a place is termed as sedimentation.
• Metamorphic Rocks : Metamorphic rocks make up a large part of the Earth’s crust and are classified by texture and by chemical and mineral assemblage. They may be formed simply by being deep beneath the Earth’s surface, subjected to high temperatures and the great pressure of the rock layers above it.

Environment is our basic life support system.
The word environment has its roots in the French word Environer / Environner which means neighbourhood. People, places, things and nature that surround any living organism are called environment.
The natural component of the atmosphere comprises of air, water, land and living things. The natural environment refers to both biotic and abiotic conditions. The biotic conditions consist of the world of living organisms e.g. plants and animals. The abiotic conditions consist of the world of non–living elements like land.
The human made component of the environment are the creations by human beings which include bridges, roads, dams, parks and monument etc.

Mantle: Mantle is the widest section of the Earth. Its thickness is approximately 2,900 km. Mantle is mainly made up of semi-molten rock known as magma. The rock is hard in the upper part of the mantle, but lower down the rock is softer and begins to melt. The mantle is located directly under the Sima. The mantle consists of very hot and dense rock. This layer of rock flows like asphalt under heavy weight. This flow is because of the greatest temperature differences from the bottom to the top of the mantle. The reason behind the plates of the Earth move is the movement of the mantle. Its temperature varies between 1600 oF at the upper part to 4000 oF near the bottom.
Crust: The crust is the outer layer where we live. The thickness is around 0-60 km. It’s a solid rock layer divided into two types: Continental crust covers the land and, Oceanic crust covers water. The crust is the most widely studied and understood. Mantle is hotter and capable of flowing. The outer and inner core are much hotter with great pressures that you can be squeezed into a ball smaller than a marble if you are able to go in the center of the Earth.

There are four domains of the environment i.e. the lithosphere, the hydrosphere, the atmosphere and the biosphere.
Lithosphere forms the solid part of the earth and contains landforms like plateaus, mountains, plains and valleys. It is made up of rocks and minerals and is covered by a thin layer of soil.  Lithosphere hence comprises the crust, core and mantle.
Hydrosphere forms the next layer and covers three-fourth of the earth in form of water bodies. The thin layer of air that surrounds the earth is called atmosphere. The atmosphere forms a protective layer and shields the earth from the strong sunrays. Primarily containing gases, the atmosphere sticks to the earth owing to earth’s gravitational force. The atmosphere consists of stratosphere and troposphere.
Biosphere is the last domain of the earth and is made up of all the plants and animals and all non-living things. It can extend up till any part of the earth where life can exist. 

 Human beings interact with the environment and modify it according to their need. Early humans adapted themselves to the nature surroundings. With time needs grewand became more varied, human learn new ways to use and change the environment. They learnt to grow crow crops, domesticate animals, and lead a settled life. The wheel was invented, surplus food was produced,barter system emerged, trade started and commerce developed.

Natural Environment: Natural environment includes the lithosphere, atmosphere, hydrosphere and the biosphere. The lithosphere is composed of rocks and minerals. Atmosphere is composed of air. Hydrosphere is composed of water. Biosphere is the narrow zone where life exists.

Our environment is changing because our needs are increasing day by day. To fulfil these needs we often don’t think about the environment and start modifying it.