USA Biology Olympiad (USABO) Practice Exam

Why is there no continuing abiotic origin of life on Earth today?

1. High levels of ultraviolet radiation

2. Presence of complex life forms

3. Insufficient atmospheric carbon dioxide

4. Our oxidizing atmosphere is not conducive to spontaneous formation of complex molecules

The correct answer is: Our oxidizing atmosphere is not conducive to spontaneous formation of complex molecules

The reasoning behind the selected answer revolves around the environmental conditions present on Earth today. During the early stages of the planet’s history, the atmosphere was vastly different than it is now, characterized by a reducing environment that may have supported the spontaneous formation of complex organic molecules. These conditions were conducive to abiotic processes that could lead to the origins of life. Today, however, the atmosphere is predominantly oxidizing, which means it is rich in oxygen and other reactive gases. This type of environment is not conducive to the spontaneous formation of complex molecules due to the tendency of oxygen to react with potential organic compounds, breaking them down rather than allowing them to combine and evolve into more complex structures. In essence, the presence of oxygen and other oxidizing agents makes it difficult for the types of reactions necessary for life to emerge abiotically. High levels of ultraviolet radiation do pose a hazard to the stability of organic compounds, but they do not fully account for the lack of abiotic origin today. The presence of complex life forms and insufficient atmospheric carbon dioxide might influence certain aspects of life, but they do not directly impact the fundamental chemical processes that are necessary for abiogenesis in the way that an oxidizing atmosphere does.