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The Origin And Evolution Of The Earth-Geography Notes For W.B.C.S Examination.
WBCS পরীক্ষা – আর্থের উৎস এবং বিবর্তন – ভূগোল নোট।
Lightyear
- It is a unit of astronomical distance which is equal to the distance light travels in one year.Continue Reading The Origin And Evolution Of The Earth-Geography Notes For W.B.C.S Examination.
- A light year is a measure of distance and not of time.
- Light travels at a speed of 300,000 km/second.
Solar system
- 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 comes the outer planets, Jupiter, Saturn, Uranus, and Neptune.
The Moon
- 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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