• The Earth is the third planet of the solar system as counted from the sun. The Earth also came into existence almost the same time as the other members of the solar system, i.e. around 4.5 billion years ago. This is the planet we live on and where multitude of diverse life forms has evolved.
• A large number of hypotheses were put forth by different philosophers and scientists regarding the origin of the earth.
• Nebular Hypothesis – One of the earlier and popular arguments was by German philosopher Immanuel Kant. Mathematician Laplace revised it in 1796. It is known as Nebular Hypothesis. The hypothesis considered that the planets were formed out of a cloud of material associated with a youthful sun, which was slowly rotating.
• Earth initially was a barren, rocky and hot object with a thin atmosphere of hydrogen and helium. This is far from the present day picture of the earth.
• The period, between the 4,600 million years ago and the present, led to the evolution of life on the surface of the planet. The earth has a layered structure.
• From the outermost end of the atmosphere to the centre of the earth, the material that exists is not uniform. The atmospheric matter has the least density. From the surface to deeper depths, the earth’s interior has different zones and each of these contains materials with different characteristics
PHYSICAL CONDITIONS NECESSARY FOR LIFE
For life to exist on a celestial body the following conditions seem to be necessary:
• Presence of some elements such as carbon (C), oxygen (O2), Nitrogen (N2) and hydrogen (H2) which are involved in the basic structures of complex molecules forming living cells.
• Suitable temperature range on its surface for sustenance of life. Most of the living organisms cannot survive at too high (>700C) or too low (<O0C) temperatures because, life processes cannot be carried out at very high and very low temperatures.
• Presence of a liquid medium, like water, which is a must for transporting nutrients inside a living body.
• Presence of a protective atmosphere having a protective layer like ozone layer, to prevent harmful radiations to reach its surface.
• On the Earth all these conditions are satisfied and hence, we have life on it
WHAT MADE EARTH A SPECIAL PLANET?
The following three factors, it seems, have contributed in this regard.
• Right distance from the Sun: The Earth stays at the right distance from the sun in an almost circular orbit. Therefore, it receives just appropriate amount of energy from the sun, so that, the temperature range on its surface is suitable for the origin and evolution of life.
• Appropriate mass and size: The Earth has appropriate mass and radius so that it could provide gravitational field sufficient enough to hold atmosphere.
• Occurrence of some natural events on Earth at right time and in desirable sequence so that a life supporting system (called Biosphere) could evolve on its surface.
INDIAN GEOGRAPHY: FACTS
The Geological History of India is complex and varied. It begins with the first formation of the earth’s crust, first deposits of sedimentary rocks, first progeny and extends up to recent alluvial deposits.
Major Geological Phases of India
• 1st phase: Characterized by the cooling and solidification of the Earth’s crust (Pre-camb-600 M.Y.) Archaean gneisses and granite crumpling of Aravallis.
• 2nd Phase: Crumpling of sediments of Dharwarian Group (Bijawars).
• 3rd Phase: Calcareous and Arenaceous deposits (Cuddapah and Vindhyan basins).
• 4th Phase: The Pro-Carboniferous glaciations formation of Gondwana rock -95% coal is found in them.
• 5th Phase: Fracturing of Gondwanaland, uplifting of Vindhyan and formation of Western Ghats.
• 6th Phase: Cretaceous Lava flow, 5 lakhs sq. km formation of the Deccan Trap.
• 7th Phase: Collision of Indian Plate (Gondwanaland) with the Asian plate (Angaraland) and for Three Successive Ranges of Himalayas.
– Himadri – Greater Himalayas – Oligocene.
– Himachal – Lesser- Himalayas – Oligocene.
– Siwalik – Outer Himalayas – Post Pliocene.
• 8th Phase: Sedimentation and alleviation of Indo-Ganga trough Pliocene and Holocene.
• 9th Phase: Down warping of Rajmahal Garo Gap and Upheaval of Indo-Ganga divide, Potwar Formation of Narmada – Tapi Trough.