Structure of the Earth( GEOGRAPHY )

THE EARTH

Earth is the third planet in the solar system in terms of distance from the Sun, and the fifth largest in size. It is also the largest amongst its planetary system’s terrestrial planets, making it the largest solid body in the solar system, and it is the only planet in the universe known to support life. The Earth was formed around 4.57 billion years ago and its largest natural satellite, the Moon, was orbiting it shortly thereafter, around 4.533 billion years ago.

THE SHAPE OF THE EARTH

The Earth’s shape is that of an oblate spheroid, with an average diameter of approximately 12,742 km (~ 40,000 km /p).

THE COMPOSITION OF THE EARTH

The mass of the Earth is approximately 5.98 ×1024 kg. It comprises of iron (35.1%), oxygen (28.2%), silicon (17.2%), magnesium (15.9%), nickel (1.6%), calcium (1.6%) and aluminum (1.5%).

THE INTERNAL STRUCTURE OF THE EARTH

The interior of the Earth, like that of the other terrestrial planets, is chemically divided into layers. The Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core.

1. Earth’s Hydrosphere
The abundance of water on Earth is a unique feature that distinguishes ‘The Blue Planet’ from the other planets in the Solar System. Approximately, 71% of the Earth is covered by water and only 29% is solid land.



The Earth’s hydrosphere mainly consists of oceans, but technically includes all water surfaces in the world, including inland seas, lakes, rivers, and underground waters. The average depth of the oceans is 3,794 m (12,447 ft), more than five times the average height of the continents.

2. Earth’s Atmosphere : It consists of the following layers:
• Troposphere - This is the lowermost part of the atmosphere in which we live, and which is the theatre for almost all the weather phenomena.
• Stratosphere - Above troposphere is the stratosphere, which is important primarily because of the presence of ozone. This layer of calm and clear air is preferred for high-speed jet flights because of the absence of air pockets.
• Mesophere - Above stratosphere is mesosphere, which is more of a transitional layer.
• Ionosphere - Above mesosphere lies the ionosphere, which has electrically conducting layers that help in radio communication.
• Exosphere - The outermost layer of the Earth’s atmosphere is known as the Exosphere.

Kinds of Rocks
Rocks are naturally occuring aggregate of minerals. The Earth’s crust and mantle are formed of rocks. The study of rocks is called Petrology. Rocks are classified by their mineral and chemical composition, texture of the constituent particles and the process by which they are formed. The transformation of one rock type to another through geographical process is called the Rock Cycle.

Types of Rocks

i. Igneous Rocks – Igneous rocks are formed when the molten magma or lava slowly cools and crystallises within the Earth’s crust. Examples of the Igneous rock are granite,basalt, etc.

ii. Sedimentary Rocks – Sedimentary rocks are formed by the deposition of organic and non-organic matter over a period of time. The process of deposition is called sedimentation. Commonly known sedimentary rocks are coal, limestone, sandstone etc.

iii. Metamorphic Rocks – Pressure and change in temprature under the Earth’s surface cause Igneous and Sedimentary rocks to undergo change. This change leads to the formation of Metamorphic Rocks.

THE WORLD WARS ( World History )

World War I (Aug 14, 1914 to Nov 11, 1919)

Major Participants
1. Germany, Austria, Hungary, Bulgaria and Turkey formed a group known as the Central powers.
2. England, France, Belgium and Serbia later joined by Russia and Italy, were known as the Allied powers.

Causes of War
The First World War was a consequence of
1. assassination of Archduke Franz Ferdinand of Austria,
2. initiation of war against Serbia by Austria,
3. mobilization of forces against Austria-Hungary by Russia.

Outcome
The Allied forces won the war, Treaty of Versailles was signed, which curbed the power of the German Empire and led to the creation of many new countries in Eastern Europe.

World War II (1939 to 1945)

Major Participants
1. Allied Powers - Britain, Russia, USA, and France.
2. Axis Powers (central powers) - Germany, Italy and Japan.

Causes of War
The Second World War was a consequence of
1. rise of the Nazi party in Germany.
2. treaty of Versailles which was against Germany.
3. the expansion policy of Japan.

Outcome
The Allied forces won the war and Germany was divided into two parts. Russia and the US became the biggest powers in the World. The end of war led to the Cold War amongst the industrialised countries.

The Cold War (1947-1991)
The Cold War refers to the period of geopolitical and economic struggle that emerged after the World War II between the US and its allies and Russia and its allies. The phase lasted from 1947 till the division of erstwhile Soviet Union in 1991. This stage was referred to as the Cold War because members of both the blocs were faced with a fear of hostile attack from its enemies. The era of cold war led to a large scale development of weapons including nuclear weapons. It also led to economic warfare and trade embargoes between nations. Japan had full support of the US and Russia supported all the erstwhile Soviet Union members. The war finally came to an end in 1991 with the dissolution of Warsaw Pact which led to the division of the Soviet Union.