9.1.3 How Oxygen Increased

The oxygen that is present in the Earth's atmosphere today is primarily a result of the process of photosynthesisThe process by which plants use light energy to produce glucose. carried out by algae and plants. During photosynthesis, carbon dioxide and water are converted into glucose (a type of sugar) and oxygen. This process can be represented by the equation:

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

carbon dioxide + water –light→ glucose + oxygen

Approximately 2.7 billion years ago, algae in the Earth's oceans began producing oxygen through photosynthesis. Initially, the oxygen produced by algae did not accumulate in the atmosphere as it reacted with various elements, such as iron, in the Earth's crust and dissolved in the oceans.

However, over time, the oxygen produced by algae gradually accumulated in the atmosphere. This increase in atmospheric oxygen was a significant event in Earth's history and is known as the Great Oxygenation Event. As oxygen levels increased, it had a profound impact on the evolution of life on Earth.

The presence of oxygen in the atmosphere enabled the evolution of more complex organisms, including plants. These plants further contributed to the production of oxygen through photosynthesis. Over the next billion years, as plants evolved and spread across the Earth, the percentage of oxygen in the atmosphere gradually increased.

The gradual increase in atmospheric oxygen provided a critical environment for the evolution of animals. Oxygen is essential for aerobic respirationA chemical process that releases energy from glucose using oxygen, occurring in mitochondria., the process by which animals extract energy from food. As oxygen levels increased, more complex animals with more energy-demanding lifestyles could evolve.

Today, oxygen makes up approximately 21% of the Earth's atmosphere, allowing for the survival and thriving of a diverse range of organisms.

Conclusion

The increase in atmospheric oxygen is attributed to the photosynthetic activities of algae and plants. Over billions of years, the production of oxygen through photosynthesis gradually led to an increase in atmospheric oxygen levels. This increase in oxygen played a crucial role in the evolution of life on Earth, enabling the development of more complex organisms, including animals.