The Origin And Evolution Of The Earth

Introduction

The origin of Earth took place around 4.54 billion years ago. The earlier theories regarding the origin and evolution of Earth are Nebular Hypothesis, Revised Nebular Hypothesis as well as Binary Theories of origin of the Earth. The modern theories of the origin of the Earth are Big Bang Theory, Star Formation Theory, Planet Formation Theory, etc. The evolution of Earth denotes how the Lithosphere, Atmosphere, and Hydrosphere of the Earth were created. It also describes how life came into existence as the Earth evolved. The origin of life on Earth took place around 3.5 billion years ago.

The Origin And Evolution Of The Earth- In-Depth Analysis

Earth was formed approximately 4.54 billion years ago. Earth has unique properties that have made life possible. It is different from the rest of the planets as it supports life. Hence, it is important to understand its origin. It was initially a large cloud of dust and gas. Thereafter, it evolved and changed its form gradually.

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The Origin of The Universe

The term ‘Universe’ refers to all the matter and space that exists. It includes both physical (electrons, protons, etc.) and non-physical (light,space, etc.) elements. Big Bang Theory explains the origin of the universe around 13.8 billion years ago.

Nebular Hypothesis

• It is an early theory of the origin of Earth. Nebular Hypothesis was given by a German philosopher, Immanuel Kant
• This theory explains the formation of the Solar System
• According to this theory, the Sun and all the planets arose from a huge cloud of dust and gas called a nebula
• This cloud collapsed because of some reason that could be passing star or supernova waves
• The dust and the gas started to collect together and formed the Sun and the planets

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Revised Nebular Hypothesis

• Nebular Hypothesis was studied again and modified by Pierre Laplace in 1796
• It is also called the Solar Nebular Disk Model
• It states that the matter that came out from the nebula and got collected in the centre formed the Sun
• There was more gravitational force in the centre, and it pulled more dust and gas resulting in a snowball effect. The centre became hotter and denser
• A Protoplanetary disc was formed around the Sun. The planets were formed as the matter accumulated gradually
• Terrestrial planets like Mercury, Venus, Earth, etc. were formed near the centre of the disc. They had metallic components like iron and nickel
• Planets like Jupiter, Neptune, Saturn, etc. were formed on the cooler edges

Binary Theories

• This theory is also called Planetesimal Hypothesis
• The Binary theory was given by Chamberlain and Moulton in 1900
• According to this theory, a star collided with the Sun. As a result, some matter separated from the Sun
• After the star moved away, the separated material gradually formed the planets. These planets started revolving around the Sun

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Big Bang Theory

• Big Bang Theory is a modern theory of the Origin and the Evolution of the Earth
• Edwin Hubble propounded this theory in the year 1920
• It is also known as the Expanding Universe Hypothesis
• It states that the universe is ever-expanding
• As per this theory, all the matter of the universe was accumulated in the centre
• It occupied a small space and had an extremely high temperature and density
• Around 13.7 billion years ago, there was a big explosion
• After the explosion, the atoms were formed and gradually energy changed to matter

Planet Formation According To Big Bang Theory

There are three stages in the formation of the Planets:

• In the first stage, there were lumps of gases in the nebula. The gravitational force formed the core and discs of gases around the core
• In the second stage, the matter condensed and formed small objects round in shape called planetesimals
• In the third stage, planetesimals formed larger bodies called planets

Evolution Of Earth

In the beginning, the Earth was very hot. It was rocky and barren. Earth’s atmosphere consists of hydrogen and helium. Over a while, the lithosphere, atmosphere, and hydrosphere were formed.

How Lithosphere Developed

The temperature of the Earth started to increase as the density increased. The matter from the center of the Earth started to separate. Materials with high density moved towards the centre of the Earth, whereas the lighter materials moved towards the surface of the Earth. This is how the three layers of the Earth:

• Crust
• Mantle and
• Core

were formed.

How Atmosphere Developed

The present state of the atmosphere was reached after the following three stages:

• First Stage: The solar winds blew away the gases such as hydrogen and helium.
• Second Stage: The interior of the Earth was extremely hot. As it started to cool, water vapour and gases such as carbon dioxide, nitrogen, methane, and ammonia came out from the interior of the Earth and formed the atmosphere. There was less oxygen in the atmosphere at this stage.
• Third Stage: Oxygen was released into the atmosphere by living organisms. Living organisms perform photosynthesis and flood the atmosphere with oxygen. The amount of carbon dioxide decreased in the atmosphere and led to condensation.

Origin Of The Life

Life originated on Earth 3800 million years ago. The first form of life was blue algae. Chemical reactions created molecules that could multiply and change into living forms.

Conclusion

There are several theories regarding the origin and the evolution of Earth. The main theories are the Nebular Hypothesis and the modern theory- Big Bang Theory. Earth was hard, rocky, and barren initially. Gradually it developed its three layers- crust, mantle, and core. The atmosphere of the earth has no oxygen in the beginning. When the living forms performed photosynthesis, the amount of oxygen increased in the atmosphere and carbon dioxide decreased. The evolution of life took place on earth with blue algae.