Structure and Formation of Earth, Study Notes, Material - All Teaching Exams

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Formation Of The Earth

There are many theories given by the scientists & philosophers concerning the origin of the earth and other planets. Some of the popular theories are:

Early Theories.

• Nebular Hypothesis.

1. This theory was given by a german philosopher, Immanuel Kant.
2. It was later revised by the mathematician Pierre-Simon Laplace in 1796.
3. The hypothesis states that planets were formed out of a cloud of material associated with a young sun that was slowly rotating.

• Planetesimal Hypothesis.

1. This hypothesis was given by Chamberlain & Moulton in 1900.
2. It suggested that a wandering star approached the sun which caused a cigar-shaped extension of material to separate from the solar surface.
3. As the passing star moved away, the material separated from the solar surface continued to rotate around the sun & slowly condensed into planets.
4. The argument was supported by Sir James Jeans and later Sir Harold Jeffrey.

• Binary Theories.

1. These arguments considered that the sun had a companion which was coexisting.
2. Revised Nebular Hypothesis.
3. This hypothesis was proposed by Carl Weizascar in Germany and Otto Schmidt in Russia.
4. They considered that the sun was surrounded by a solar nebula and the nebula consisted mainly of hydrogen, helium and something called dust.
5. The collision of particles & the friction caused the formation of a disk-shaped cloud & planets were created through the accretion process.

Modern Theories.

Big Bang Theory.

1. It is also known as the expanding universe hypothesis.
2. The theory was given by Edwin Hubble in 1920.
3. According to this theory, in the beginning, all the matter or substance that formed this universe existed in one place as a tiny ball (single atom). This tiny ball had a very small volume, infinite density and temperature.
4. The event of Big Bang took place about 13.7 billion years ago.
5. At the Big Bang, this tiny ball exploded which led to a huge expansion and this process of expansion continues till present.
6. As the expansion grew, some of the energy was converted into matter.
7. Rapid expansion took place within seconds after the Bang forming clusters of galaxies, which then exploded to form stars & stars further exploded to form the planets.

Structure of the Earth.

Earth has formed about 4.5 million years ago. Earth is the fifth-largest planet in our solar system. The surface of the earth is mostly made up of rock & metal. The temperature of the earth keeps increasing with an increase in depth. After every 32 meters inside, the temperature is increased by 1°. It is consists of three layers:

• The Crust
• The Mantle
• The Core

1. The Crust.

• It is the uppermost layer of the earth’s surface and it is also the thinnest of all layers.
• It is a solid layer where all life forms exist like mountains, sea and soil, also known as the lithosphere.
• Its made up of rocks.
• The depth of the crust lies between 5-35 km.
• The thickness of earth’s crust varies in oceanic & continental areas.
• The continental crust holds a thickness of about 35 km whereas the oceanic crust contains a thickness of only 5km.
• The continental crust (land) mostly consists of sedimentary & granite rock that overlies the basalt rock.
• The oceanic crust contains only basalt rock.
• The major constituent minerals found in the continental crust are Silica & Aluminium, thus it is also called SIAL.
• The oceanic crust mainly contains minerals, Silica & Magnesium, thus it is also called SIMA.

2. The Mantle.

• It is the middle layer of the earth’s surface which is situated right below the crust.
• The mantle is about 2900 km deep.
• It is made up of heavy & denser rocks that are moldable due to the heat inside the mantle which causes these rocks to melt into a semi-solid layer.
• It is further divided into two layers i.e. Upper Mantle & Lower Mantle.
• The thickness of the upper mantle is between 100 to 200km and it is also known as the asthenosphere.
• The thickness of the lower mantle extends from 660 to 2900 km hence it is ideal for the formation of minerals due to its hot temperature & density.
• The main constituents minerals of the mantle are molten Silica, Magnesium & Iron.

3. The Core.

• It is the innermost layer of the earth’s surface and it is covered by the lower mantle.
• When the earth was formed, heavy substances sunk down forming the core of the earth.
• It is also called the center of the planet and it is way hotter & denser than the other two layers.
• It is mostly made of metal such as iron & nickel and also called NIFE.
• The core has two layers i.e. Outer Core & Inner Core.
• The depth of the outer core ranges from 2900 km to 5100 km and iron & nickel are found in the liquid-state.
• The depth of the inner core lies beyond 5100 km and contains pure iron & nickel in the solid-state as it contains the densest, heaviest & most compact matter.
• As a result of the outer core containing liquid iron, floating around the solid inner core, the magnetic field of the earth is formed.

This article tends to be beneficial for the following exams - REET, UPTET, CTET, Super TET, DSSSB, KVS etc.

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