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Origin and Evolution of Life — BIOLOGY STD 12 Science — Question

Maharashtra BoardEnglish MediumSTD 12 ScienceBIOLOGYOrigin and Evolution of Life3 Marks
Question
When did Earth originate? Which transformations took place later?
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Answer

  1. Earth originated about 4.6 billion years ago as a part of the solar system.
  2. When it was formed, it was a rotating cloud of hot gases and cosmic dust. It was then appearing like a nebula.
  3. Later the condensation and cooling started which resulted in stratification.
  4. Heavier elements like nickel and iron settled to the core. Lighter elements like helium, hydrogen, nitrogen, oxygen, carbon, etc. remained on the surface and they formed the primitive atmosphere.
  5. This atmosphere of the earth was of a reducing type, devoid of free oxygen and very hot.

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