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Question

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?
(a) 1 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3

Answer:

C

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Explanation:

Statement 1 is correct. The Earth's magnetic field has indeed reversed several times throughout its history. This phenomenon, known as magnetic field reversal or geomagnetic reversal, is a natural process where the Earth's magnetic poles switch places. These reversals have occurred irregularly over geological time scales, with the most recent one occurring approximately 780,000 years ago.

Statement 2 is incorrect. When the Earth was formed more than 4 billion years ago, the atmosphere was primarily composed of gases such as nitrogen, carbon dioxide, water vapor, and small amounts of methane and ammonia. Oxygen, as we know it today, started accumulating in the atmosphere only after the emergence of photosynthetic organisms.

Statement 3 is correct. When living organisms originated, they played a significant role in modifying the early atmosphere of the Earth. Through the process of photosynthesis, certain microorganisms, such as cyanobacteria, released oxygen as a byproduct. This activity gradually led to the buildup of oxygen in the atmosphere, which eventually facilitated the development of oxygen-dependent life forms.

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