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From water to Earth: How did oxygen abundance affect the evolution of life?
In the universe, the abundance of a chemical element is a measure of its occurrence relative to all other elements in an environment. There are generally three ways to measure this richness: mass fraction, mole fraction, and volume fraction. When discussing life on Earth, oxygen abundance plays a crucial role, influencing many chemical reactions and the evolution of life.
Hydrogen and helium are the most abundant elements in the universe, accounting for approximately 98% of the mass of the universe. And oxygen, the third most abundant element, sparked the evolution of life on Earth and in its waters.
From a cosmic perspective, the abundance of oxygen affects the formation and evolution of stars. About 74% of the matter in the universe is hydrogen, and helium accounts for about 24%. These elements were formed in the early stages of the universe after the Big Bang, followed by the creation of heavier elements such as oxygen in supernova explosions. Key to this process is nuclear fusion. These reactions take place inside stars, and it is in these extreme environments that oxygen is formed.
As the Earth formed, its constituent elements also showed different characteristics from other planets. The Earth is mostly made up of heavier elements such as iron, oxygen and silicon, and the dispersion of these elements gave life the soil it needed for the first time. In the earth's crust, the mass fraction of oxygen is as high as 46%, while silicon is 28%. The presence of these elements allowed the formation of rocks and minerals on the Earth's surface, creating an environment suitable for the development of life.
Oxygen's high reactivity allows it to form a variety of compounds with other elements. These compounds are the basis of biochemical reactions and in turn catalyzed the evolution of life.
Today, water is the most important element required by living things. The chemical composition of water is H2O, and the mole fraction of oxygen in water is 33%. The presence of water not only acts as a medium for chemical reactions in living organisms, but also maintains many important biological processes in ecosystems. Since the earth's water resources mainly exist in liquid form, the abundance of oxygen makes the earth the only planet with life.
Oxygen also plays an important role in the Earth's atmosphere. Oxygen in the atmosphere comes primarily from photosynthesis in plants, a process that converts carbon dioxide and water into oxygen and energy. Over time, these plants continue to release oxygen, eventually increasing the volume fraction of oxygen in the atmosphere to about 20.9%. This change not only supports the breathing of animals, but also provides the conditions for the survival of diverse life on earth.
From the existence of oxygen, we see the formation of an ecological chain. The cooperation of all links in this chain allows life to flourish.
Historically, the evolution of oxygen abundance has also affected the diversity of life. As the earth evolves and organisms adapt, the increase in oxygen promotes catastrophes of life and the emergence of new species again and again. There is growing evidence that oxygen abundance facilitated the birth of more complex organisms, including large animals.
However, with the rise of humans, oxygen abundance faces new challenges. The increase in pollutants and carbon dioxide released by industrial activities may affect the balance of the ecosystem, thereby affecting the oxygen cycle. Therefore, understanding oxygen concentration and its role in the evolution of life will be one of the tasks we face.
Ecological research also shows that changes in oxygen may affect not only individual species, but also the overall health of the ecosystem.
In general, from oxygen in water to the role of oxygen in the earth, we can clearly see how past and present environmental changes affect the evolution and development of life. Oxygen is not only an element we need, but its abundance also determines the Earth's biodiversity and ecological stability. While thinking about all this, we have to ask, how will the earth in the future evolve new life forms due to the abundance of oxygen?
