Theories About Origin of Earth: Evolution of Earth and Its Theory
There are different Theories About Origin of Earth Different philosophers and scientists give a large number of hypotheses.
The origin and evolution of the Earth are known to occur approximately 4.54 billion years back. Earth is a unique planet with properties that support life, making it different from other planets. Earlier, Earth contained a large cloud of gas and dust. The origin of life on Earth occurred roughly 3.5 billion years ago. Theories About Origin of Earth gives the idea how the Atmosphere, Hydrosphere, and Lithosphere of the Earth were formed.
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The early theories regarding the origin and evolution of the Earth are the Nebular Hypothesis, the Revised Nebular Hypothesis, and Binary Theories of the origin of the Earth. The recent theories of the origin of Earth are Planet Formation Theory, Star Formation Theory, Big Bang Theory, etc. In this article, understand the origin and evolution of the Earth, theories of its origin, formation of Earth and planets in detail.
Table of Contents
Nebular Hypothesis
The nebular Hypothesis was given by German philosopher Immanuel Kant.
Nebular hypothesis considered that the planets were formed out of a cloud of material associated with a youthful sun, which was slowly rotating.
In 1950, Otto Schmidt in Russia and Carl Weizascar in Germany somewhat revised the ‘nebular hypothesis.
They considered that the sun was surrounded by a solar nebula containing mostly hydrogen and helium along with dust. The friction and collision of particles led to the formation of a disk-shaped cloud and the planets were formed through the process of accretion.
Binary Theory
In 1900, Chamberlain and Moulton considered that a wandering star approached the sun. As a result, a cigar-shaped extension of material was separated from the solar surface. As the passing star moved away, the material separated from the solar surface continued to revolve around the sun and it slowly condensed into planets. This argument is also supported by Sir James Jeans and later Sir Harold Jeffrey
At a later date, the arguments considered of a companion to the sun to have been coexisting.
Formation of Planets
The following are considered to be the stages in the development of planets :
- The stars are localised lumps of gas within a nebula. The gravitational force within the lumps leads to the formation of a core to the gas cloud and a huge rotating disc of gas and dust develops around the gas core.
- In the next stage, the gas cloud starts getting condensed and the matter around the core develops into small- rounded objects. These small-rounded objects by the process of cohesion develop into what are called planetesimals. Larger bodies start forming by collision, and gravitational attraction causes the material to stick together. Planetesimals are a large number of smaller bodies.
- In the final stage, these large numbers of small planetesimals accrete to form fewer large bodies in the form of planets.
Evolution of the Earth
The earth was a barren, rocky and hot object with a thin atmosphere of hydrogen and helium.
- Lithosphere – With the increasing density, the temperature inside the earth increased and the materials started getting separated depending on their densities. The heavier elements like iron moved towards the centre and lighter ones moved towards the surface. With the passage of time the earth cooled, solidified and condensed into a smaller size and formed the crust (the outer layer of the earth).
- The different layers of the earth starting from the surface are crust, mantle, outer core and inner core. From crust to the core, density increases.
- Atmosphere – The solar wind was most intense nearer the sun; so it blew off lots of gas and dust from the terrestrial planets – Mercury, Venus, Earth and Mars. During the process of cooling of earth, gases and water vapour escaped from the interior of the earth thereby starting the evolution of the present atmosphere. The early atmosphere mainly had water vapour, carbon dioxide, nitrogen, methane, ammonia and small amounts of free oxygen. The process of release of gases from the interior of the earth is called “degassing”.
- Hydrosphere – The frequent volcanic eruptions provided the atmosphere with water vapour and gases. With the cooling of the earth, water vapours condensed and brought rain. The carbon dioxide in the atmosphere got dissolved in rainwater which further lowered the temperature leading to more condensation and more rain. The rain water got collected into depressions to give rise to oceans. Life was limited to oceans only for a long time. Oceans got saturated with oxygen through the process of photosynthesis and then some 2,000 million years ago oxygen began to flood the atmosphere.
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).Mesozoic65 – 245MillionPaleozoic240 – 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 ManHomo SapiensEarly 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 | PreCambrian 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 Million12,000 Million13,700 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.