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Q57 (IAS/2018) Geography › World Physical Geography › Atmosphere composition Official Key

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 ?

Result
Your answer: —  Â·  Correct: C
Explanation

The correct answer is (c) 1 and 3 only.

Statement 1 is correct: The Earth's magnetic field has indeed reversed its polarity many times throughout geological history, roughly every few hundred thousand years. This phenomenon is called geomagnetic reversal and is well-documented in the rock record through paleomagnetism.

Statement 2 is incorrect: When the Earth was formed about 4,600 million years ago, the early atmosphere had NO free oxygen and was rich in carbon dioxide, methane, ammonia, and water vapour. The current oxygen-rich atmosphere is largely a result of photosynthesis by cyanobacteria (Great Oxygenation Event ~2.4 billion years ago).

Statement 3 is correct: Living organisms, particularly photosynthetic organisms like cyanobacteria, fundamentally modified the early atmosphere by releasing oxygen and consuming carbon dioxide. This transformation enabled the evolution of aerobic life.

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Q. Consider the following statements : 1. The Earth's magnetic field has reversed every few hundred thousand years. 2. When the Earth was …
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Origin: standard textbook Fairness: fair Books / CA: 9/10 · 0/10
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Pure science question based on NCERT Class 11 Geography (Fundamentals of Physical Geography) and Class 12 Biology. Earth's early atmosphere composition and geomagnetic reversals are standard textbook topics.

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