Final answer:
The composition of Earth's atmosphere has changed drastically over time, transitioning from an atmosphere dominated by carbon dioxide to one that now contains more nitrogen. The key agent in this transition has been the proliferation of life, specifically photosynthesizing organisms that contribute oxygen to the atmosphere.
Step-by-step explanation:
The Earth's atmosphere has significantly changed since it first formed. The atmosphere of the early Earth was very different from today's atmosphere. It originally lacked O₂ and consisted mostly of CO₂. However, due to geological changes and the advent of photosynthesizing life forms, the composition of the atmosphere changed over time.
Through photosynthesis, life forms were able to convert CO₂ into O₂, leading to an increase in atmospheric oxygen. Plus, the proliferation of these life forms led to the release of more oxygen than natural chemical reactions could remove from the atmosphere. As a result, Earth finds itself with a nitrogen-rich atmosphere as CO₂ was removed and deposited in marine sediments.
Therefore, option B is correct: The atmosphere now contains much more nitrogen than the initial atmosphere. This shift in composition has not only helped support life as we know it, but also influenced Earth's temperature and climate patterns.
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