NCERT notes on important topics for the IAS aspirants. These notes will also be useful for other competitive exams like banking PO, SSC, state civil services exams and so on. This article talks about the Geography as an assimilating discipline as a science of spatial characteristics and Divisions of geography and significance of physical geography
- It is a unit of astronomical distance which is equal to the distance light travels in one year.
- A light year is a measure of distance and not of time.
- Light travels at a speed of 300,000 km/second.
- Solar system consists of eight planets.
- Mercury, Venus, Earth, Mars, Jupiter, Uranus, Saturn and Neptune.
- The inner planets are Mercury, Venus, Earth, and Mars.
- After an asteroid belt come the outer planets, Jupiter, Saturn, Uranus, and Neptune.
- The moon is the only natural satellite of the earth.
Evolution of the Earth
- The age of Earth is approximately one-third of the age of the universe.
- Earth formed around 4.54 billion years ago by accretion from the solar nebula.
Lithosphere, Atmosphere, and Hydrosphere of the Earth
- Lithosphere: The firm outer part of the earth, comprising of the crust and upper mantle.
- Atmosphere: A layer of gases encircling a planet that is seized in place by the gravity of that body.
- Hydrosphere: It is the collective mass of water found on, under, and above the surface of the earth.
- The first stage of the evolution of Lithosphere, Atmosphere, and Hydrosphere is marked by the loss of primordial atmosphere.
- In the second stage, the hot interior of the earth contributed to the evolution of the atmosphere.
- Finally, the composition of the atmosphere was modified by the living world through the process of photosynthesis.
- The present composition of earth’s atmosphere is chiefly contributed by nitrogen and oxygen.
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