The early atmosphere on Earth is thought to have lacked which of the following gases?

• A. Methane
• B. Carbon dioxide
• C. Water
• D. Nitrogen
• E. Oxygen

Answer: (E)

Verified step by step guidance

1. Understand the context: The early atmosphere of Earth refers to the period shortly after the planet formed, approximately 4.5 billion years ago.
2. Identify the gases present: The early atmosphere was primarily composed of gases released from volcanic activity, such as methane (CH₄), carbon dioxide (CO₂), water vapor (H₂O), and nitrogen (N₂).
3. Recognize the absence of oxygen: Oxygen (O₂) was not a significant component of the early atmosphere. It became abundant only after the evolution of photosynthetic organisms, which released oxygen as a byproduct.
4. Consider the role of photosynthesis: Photosynthetic organisms, such as cyanobacteria, began producing oxygen through the process of photosynthesis, which gradually increased the oxygen levels in the atmosphere.
5. Conclude the analysis: Based on the historical development of Earth's atmosphere, oxygen was the gas that was initially absent in the early atmosphere.