Origin and Evolution of the Earth – Nebular Hypothesis, UPSC Notes

Early Theories of Origin and Evolution of the Earth

Below are the early theories of the origin of Earth that happened since 1796 and continued till 1950. The theories of the original and evolution of the Earth have always been a matter of discussion. Check here the list of the accepted theories-

Theories of Origin of Earth	Year
Nebular Hypothesis	1796
Formation of Planets	1900
Revised Nebular Hypothesis	1950

Nebular Theory of Laplace – Nebular Hypothesis

Immanuel Kant developed the Nebular Hypothesis, which Pierre Laplace revised in 1796. According to the Nebular Theory of Laplace, the planets were created from the cloud material associated with a gradually rotating sun.

Additional Theories of Origin and Evolution of the Earth

Moulton and Chamberlain assumed that a moving star came closer to the Sun and formed a cigar-shaped extended matter in 1900, which was eventually detached from the solar system.

• The material that got parted away continued to revolve around the Sun and slowly condensed to form planets.
• The binary theory of the origin of Earth is regarded as a counterpart coexisting with the Sun.
• Carl Weizascar (in Germany) and Otto Schmidt (in Russia) reworked the Nebular Hypothesis in 1950.
• According to the new theory, the Sun got enveloped by a solar nebula comprising Helium, Hydrogen, and dust.
• The collision and friction of particles pushed the creation of a disk-like cloud and planets through agglomeration.

Binary Theory of Origin of Earth

Planetesimal Hypothesis is also a binary theory, and Moulton and Chamberlain presented the theory of Binary in 1900. As per the Binary theory, a star hits the Sun, causing the materials to get disjoined from the Sun. This is one of the widely accepted theories stating the origin and evolution of the Earth.

• The star was assumed to move away, and the separated particles formed the planets.
• These planets began revolving around the Sun.

Modern Theory – The Big Bang Theory

The modern theory solved the problems of the universe’s origin, while the early theories concentrated on the origin and evolution of the Earth.

• Big Bang Theory is also known as the expanding universe hypothesis.
• Edwin Hubble offered proof that the universe was growing in 1920.
• Due to expansion, the overall distance between Galaxies increased over a duration of time.

The Big Bang theory stated that:

• Every particle or matter that created the universe was present in one place, having an area less than that of an atom with unbelievably small volume, infinite density, and temperature.
• About 13.7 billion years ago, the matter blasted with a big bang.
• The first atom was developed just 3 minutes after the big bang occurrence.
• The energy released during the event got transformed into matter.
• The universe became transparent after the creation of atomic matter.

Evolution of Earth

The Earth was considered very warm initially, consisting of infertile and rocky ground. The atmosphere of Earth is comprised of gases like Helium and Hydrogen. The atmosphere, hydrosphere, and lithosphere were created during the origin and evolution of the Earth.

Evolution of Lithosphere

The distinct layers of the Earth from the surface are the crust, mantle, outer core, and inner core. There is an increase in density from the Earth’s outer surface to the centre.

• As the density increases, the Earth’s inner temperature increases, and the particles get separated from each other based on their densities.
• The lighter elements move towards the surface, and dense materials, for example, iron, shift towards the centre.
• The Earth’s outer layer or crust is formed when it cools down, solidifies, and condenses into a small size over a span of time.

Atmosphere of Earth

The atmosphere initially comprised nitrogen, carbon dioxide, free oxygen, water vapour, methane, and ammonia. Degassing was one method that caused the release of gas from the Earth’s interior part. This forms an eminent part of the origin and evolution of the Earth.

• The solar breeze was strong close to the Sun; hence it blew large amounts of dust and gases from terrestrial planets.
• During Earth’s cooling process, water vapours and gases exited from the internal surface, leading to the evolution of the current atmosphere.

Components of Hydrosphere

The oceans were flooded with oxygen because of Photosynthesis, which later entered the atmosphere around 2,000 million years back.

• Huge quantities of precipitation filled the depressions with rainwater, giving rise to several oceans.
• More rain took place as carbon dioxide in the atmosphere dissolved in rainwater, leading to a decrease in temperature and condensation.
• Because of recurring volcanic eruptions, the atmosphere contains enormous amounts of gases and water vapour.
• As the Earth cooled down, these water vapours condensed into water droplets bringing rainfall.

Origin and Formation of Earth

The Earth is understood to be formed due to an explosion approximately 4.5 billion years ago. It was a white mass consisting of dust and gas having a burning hot temperature. Here, is the origin and the evolution of the Earth have been listed here-

• Both gas and dust particles slowly formed solid rocks by condensation over the passing years.
• The shrinking or condensation event heated the Earth and caused the rocks to melt into a sticky liquid.
• The Earth’s crust (or the outer surface) cooled down and formed hard rock again by solidification upon cooling after millions of years.
• The Earth’s interior surface remained extremely hot.
• The crust became stiffened and created land after the Earth’s cooling process.
• Water vapours in the atmosphere got condensed into liquid water, supplying the depressions to form oceans.

Stages in the Formation of Planets

Below are the three stages that occurred during the formation of planets in the solar system. Each stage witnessed numerous changes that led to the formation of the Earth.

First Stage

The star was a gas bubble within the nebula. The bubble formed a core, and the large rotating discs of dust and gases around the gaseous core were due to the gravitational force.

Second Stage

The particles surrounding the core formed globular small objects after getting condensed. These were referred to as Planetesimals.

Final Stage

A large number of smaller Planetesimals bodies became larger planet bodies after the collision process.

Origin of Solar System and its Characteristics

The formation of the Solar System started 5 billion years ago. It incorporates nine planets, asteroids and comets, several satellites, and the Sun.

• Planets revolve around the Sun in specified elliptic orbits.
• The total number of planets is of two types.
• One is terrestrial or Earth-like planets which include Mercury and Venus.
• The second is Julian, or giant planets, for example, Uranus and Neptune.
• The main difference between the types of planets is based on their size and their atmospheric composition.

The number of satellites each planet possess is listed in the table given below.

Planet of Solar System	Number of Satellites
Mercury	Zero
Venus	Zero
Earth	1
Mars	2
Jupiter	53
Saturn	53
Uranus	27
Neptune	13

Difference between Julian and Terrestrial planets

All 9 planets of the solar system are broadly divided into two types based on their formation, size, and composition of atmosphere.

Criteria	Julian planets	Terrestrial planets
Another name	Outer or giant planets	Inner or Earth-like planets
Formation	It is formed by gaseous particles.	They are formed by solid particles
Removal of matter	No removal occurs on Jovian planets.	Solar winds blow off large amounts of dust and gases from these planets.
Size	They are larger in size.	The size of planets is small.
Atmosphere	Thick atmosphere made of helium and hydrogen.	Thinner atmosphere.
Examples	Saturn, Jupiter, Neptune, Pluto, and Uranus.	Mars, Earth, Venus, Mercury,

Geological Time Scale – Evolution of Earth

The evolution of life from unicellular bacteria to modern human beings is given in the table below depicting Geological Time Scale.

Age	Era	Period	Generation	Years/Age before Present (in Millions)	Major Life Events
	Cainozoic (from 65 million years to the current times). Mesozoic 65 – 245 Million Paleozoic 240 – 570 Million	Quaternary Tertiary Cretaceous Jurassic Triassic Permian Carboniferous Devonian Silurian Ordovician Cambrian	Holocene Pleistocene Pliocene Miocene Oligocene Eocene Palaeocene	0 – 10,000 Million 10,000 – 2 Million 2 – 5 Million 5 – 24 Million 24 – 37 Million 37 – 58 Million 57 – 65 Million 65 – 144 Million. 144 – 208 Million. 208 – 245 Million. 245 – 286 Million 286 – 360 Million 360 – 408 Million. 408 – 438 Million. 438 – 505 Million 505 – 570 Million.	Modern Man Homo Sapiens Early Human Ancestor. Ape: Flowering plants and Trees. Anthropoid Ape. Hare and Rabbits. Short Mammals: Mice and Rats. Dinosaurs Extinction. Age of Dinosaurs. Turtles and Frogs. Reptiles dominate – substitute amphibians. New reptiles: Vertebrates: coal beds. Amphibians. New trace of life on land; Plants. First fish. No terrestrial life: Marine invertebrate.
Proterozoic Archean Hadean	Pre-Cambrian 570 – 4800 Million			570 – 2500 Million 2500 – 3800 Million 3800 – 4800 Million.	Arthropods with soft bodies. Blue-green algae: unicellular bacteria. Formation of continents and Oceans: Atmosphere and oceans rich in carbon dioxide.
Origin of Stars Supernova Big Bang	5000 – 13,700 Million.			5000 Million 12,000 Million 13,700 Million.	Sun Origin. Universe Origin.

The Origin and Evolution of the Earth UPSC

The origin and evolution of the Earth is an important topic for the Civil Services exam. Aspirants can check out the Geography Notes for UPSC to glimpse at the noteworthy facts that will cover the entire Geography syllabus.

The origin and evolution of the Earth notes will be helpful for several competitive exams in the country, including banking PO, SSC, state civil services, and many more. Candidates should understand every aspect of the topic, including early and modern theories of the origin of the Earth, the formation of planets and Earth, etc., so they can answer all the questions asked in the UPSC Exam.

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