The presence of oxygen (O2) can hinder pre-biotic chemical reactions for several reasons:
Oxidation: Oxygen is a highly reactive molecule, and in the presence of other chemicals, it can readily react with them through oxidation. Many of the molecules and compounds thought to be important in pre-biotic chemistry, such as simple organic molecules, are susceptible to oxidation. This means that instead of forming the desired molecules, they might react with oxygen to form other compounds, disrupting the desired pathways.
Destruction of Organic Molecules: Oxygen can break down organic molecules. In the early Earth environment, before life evolved and the atmosphere was oxygen-rich, organic molecules could have formed more easily. However, once oxygen was present in the atmosphere due to photosynthetic organisms, these molecules could have been broken down by reactions with oxygen, making it difficult for them to accumulate and participate in pre-biotic chemistry.
Competition for Reactions: Oxygen can also compete with other molecules for the reactions needed for pre-biotic chemistry. If oxygen is present, it might preferentially react with certain molecules, preventing those molecules from participating in the desired reactions.
Effects on Catalysts: Some proposed pre-biotic reactions require specific catalysts. Oxygen can interfere with these catalysts or deactivate them, preventing the reactions from proceeding.
Formation of Stable Compounds: When oxygen reacts with certain molecules, it can form stable, non-reactive compounds. This means that the reactive molecules needed for pre-biotic chemistry may be "used up" in reactions with oxygen, reducing their availability for other reactions.
Overall, the presence of oxygen in pre-biotic environments can be problematic for the formation of the complex organic molecules thought to be necessary for the origin of life. This is one of the reasons scientists look for environments without oxygen, such as certain deep-sea hydrothermal vents or simulated early Earth conditions in laboratories, to study pre-biotic chemistry.
