Consider the following statements :
- 1.The Earth’s magnetic field has reversed every few hundred thousand years.
- 2.When the Earth was created more than 4000 million years ago, there was 54% oxygen and no carbon dioxide.
- 3.When living organisms originated, they modified the early atmosphere of the Earth.
Which of the statements given above is/are correct ?
Show answer
Answer: C. Statement 1 is correct: the Earth's magnetic field has reversed many times, on average every few hundred thousand years. Statement 2 is wrong: the early atmosphere had almost no free oxygen; oxygen came later from photosynthesis. Statement 3 is correct: living organisms, through photosynthesis, changed the atmosphere. So 1 and 3.
Watch for: The precise '54% oxygen' figure looks scientific, but early Earth's air lacked oxygen.
Why the other options are wrong
- A. Wrong because statement 1 is correct too.
- B. Wrong because the early atmosphere had no free oxygen.
- D. Wrong because statement 2 is false.
Source to check: NCERT Class 11 'Fundamentals of Physical Geography', Chapter 2 'The Origin and Evolution of the Earth' (Evolution of Atmosphere)
Answer from the official UPSC key. Written and fact-checked by AI against the official key. Spotted a mistake? Report it.