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?
✓ Correct answer: c) 1 and 3 only
ExplanationStatement 1 is correct: The Earth’s magnetic field has undergone numerous reversals over geological time scales.These geomagnetic reversals occur at irregular intervals averaging approximately every 300,000 years though it varies.Statement 2 is incorrect: Over 4000 million years ago earth’s early atmosphere lacked oxygen and was primarily composed of gases like methane, ammonia, water vapor, and carbon dioxide.The current level of oxygen (around 21%) accumulated much later due to photosynthetic activity by living organisms.Statement 3 is correct: Living organisms particularly cyanobacteria played a significant role in modifying the Earth’s early atmosphere by producing oxygen through photosynthesis.This process led to the Great Oxygenation Event around 2.4 billion years ago.This marked a pivotal shift from an oxygen-poor to an oxygen-rich atmosphere, profoundly influencing the evolution of life.170
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