UPSC CSE Prelims
Question 66
Consider the following statements :
- The Earth's magnetic field has reversed every few hundred thousand years.
- When the Earth was created more than 4000 million years ago, there was 54% oxygen and no carbon dioxide.
- When living organisms originated, they modified the early atmosphere of the Earth.
Which of the statements given above is/are correct ?
View correct answer and explanation
Correct answer: C
Correct Option: C
Explanation: Earth’s magnetic polarity has reversed many times in geological history, irregularly over hundreds of thousands of years. Early Earth lacked the alleged oxygen-rich air; photosynthetic life profoundly changed atmospheric chemistry.
Statement/Pair-wise Analysis:
Statement/Item 1: Correct - Geomagnetic reversals have recurred at irregular intervals in the geological record.
Statement/Item 2: Incorrect - The early atmosphere contained little free oxygen; the claim of 54% oxygen and no CO₂ is false.
Statement/Item 3: Correct - Photosynthetic organisms progressively oxygenated and altered Earth’s atmosphere.
Option-wise Analysis:
A: Incorrect - omits correct statement/item 3.
B: Incorrect - includes incorrect statement/item 2; omits correct statement/item 1.
C: Correct - includes all and only the true statements/items.
D: Incorrect - includes incorrect statement/item 2.