Correct Option (c)
Explanation
Statement 1 is correct. Geological and paleomagnetic evidence indicates that Earth's magnetic field undergoes periodic reversals, where the magnetic north and south poles swap positions. These geomagnetic reversals occur irregularly but typically happen every few hundred thousand years, with the average interval being approximately 200,000 to 300,000 years.
Statement 3 is correct. When living organisms originated on Earth, they profoundly modified the planet's early atmosphere. The primitive atmosphere was largely anoxic. The emergence of photosynthetic organisms, particularly cyanobacteria, led to the release of free oxygen into the atmosphere through the process of photosynthesis. This gradual accumulation of oxygen, known as the Great Oxygenation Event (approximately 2.4 billion years ago), fundamentally altered the atmospheric composition, paving the way for the evolution of aerobic life forms.
Incorrect Options
Statement 2 is incorrect. When Earth was created approximately 4.5 billion years ago, its primitive atmosphere was vastly different from today's. It was primarily composed of gases like carbon dioxide, water vapor, methane, and ammonia, with very little to no free oxygen. The claim of 54% oxygen and no carbon dioxide is factually inaccurate for the early Earth's atmosphere. Oxygen accumulated much later due to biological activity.
Option (a) is incorrect because it only includes statement 1 and omits the correct statement 3.
Option (b) is incorrect because it includes the factually incorrect statement 2.
Option (d) is incorrect because it includes the factually incorrect statement 2.