Why were only anaerobic organisms able to live during the first 2 billion years on Earth?

• A. Anaerobic organisms could not survive in the presence of water.
• B. The atmosphere lacked oxygen, which is essential for aerobic organisms.
• C. Anaerobic organisms were the only life forms capable of photosynthesis.
• D. The atmosphere lacked oxygen, which is toxic to anaerobic organisms.

Answer: (B)

Verified step by step guidance

1. Understand the conditions of early Earth: During the first 2 billion years, Earth's atmosphere was very different from what it is today. It lacked free oxygen (O2), which is crucial for aerobic respiration.
2. Define anaerobic organisms: Anaerobic organisms are those that do not require oxygen for survival. They can live and thrive in environments devoid of oxygen.
3. Consider the implications of an oxygen-free atmosphere: Since there was no oxygen in the atmosphere, aerobic organisms, which rely on oxygen for their energy production processes, could not survive.
4. Recognize the role of anaerobic organisms: Anaerobic organisms were well-suited to the early Earth's conditions because they could obtain energy through processes that do not involve oxygen, such as fermentation.
5. Conclude why anaerobic organisms thrived: The absence of oxygen in the early atmosphere meant that anaerobic organisms were the only life forms capable of surviving and thriving during this period, as they were not dependent on oxygen for their metabolic processes.