Where does Earth’s oxygen come from? Earth has been in existence for 4.6 billion years. After the Big Bang, Earth initially formed as a “fiery sphere” constantly being burned, but after 1.1 billion years, it cooled down, and life gradually emerged, leading to the formation of the atmosphere.
When the atmosphere first formed, it did not contain oxygen. Initially, the atmosphere was filled with gases like ammonia and methane. Oxygen in the atmosphere was primarily generated through two processes: photosynthesis by plants and non-biological processes during the photodissociation of water.
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Currently, we know that oxygen constitutes approximately 21% of the air and is crucial for humans and other organisms. In an oxygen-deprived environment, humans cannot breathe properly.
So, what would happen if the oxygen levels on Earth suddenly doubled, reaching about 40% of the air?
How would different oxygen levels in the air affect humans? At oxygen levels between 0% and 10%, humans would experience difficulty breathing, a continuous decrease in oxygen saturation in the blood, impaired cognition, confusion, and eventually death due to oxygen deprivation.
At oxygen levels between 10% and 16%, humans would also find it hard to breathe, experience chest tightness, and even cardiac arrest.
At oxygen levels ranging from 15% to 19%, humans would feel dizzy, experience lightheadedness, difficulty concentrating on tasks, and studying.
At oxygen levels between 19% and 24%, the air would be within the normal range, and humans could live, work, exercise, and rest normally.
When oxygen levels reach 24% to 31%, the environment becomes highly oxygen-rich, providing the most suitable conditions for human habitation. Humans would feel alert, energetic, and experience improved sleep.
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At oxygen levels between 31% and 52%, the high oxygen concentration would accelerate the aging process, reduce lifespan, and make the body susceptible to diseases such as pneumonia and retinal damage caused by oxygen.
At oxygen levels between 52% and 90%, humans would feel restless initially, but eventually suffer from oxygen toxicity and respiratory failure leading to death.
At oxygen levels between 90% and 100%, oxidation would occur at an accelerated rate, resulting in immediate fatality for humans.
If the oxygen levels on Earth were to double, corresponding to oxygen levels between 31% and 52%, although the human body might adapt slowly, long-term and unpredictable damages would undoubtedly emerge.
Earth’s History: High Oxygen Environments In fact, Earth once had a high-oxygen environment with a concentration of around 40%.
Over 300 million years ago, during the late Carboniferous period, Earth’s environment was drastically different from today. The continents were joined together, forming a supercontinent known as Pangea.
The emergence of lignin gave rise to a significant number of vascular plants, and true trees evolved. The Earth’s surface was covered in forests dominated by ferns, and through photosynthesis, plants absorbed carbon dioxide and released oxygen, resulting in an atmosphere with high oxygen levels, reaching approximately 45% at that time, which was double the present-day levels.
The High Oxygen Environment: Giant Insects and Amphibians During the late Carboniferous period, the dominant terrestrial life forms were not dinosaurs but rather giant insects and amphibians. The high oxygen levels during the Carboniferous period played a crucial role in driving the evolution of insects.
Although the eggs of amphibians are not covered by a hard shell and occasionally they have to return to water to moisten their skin, amphibians have also evolved to large sizes because they have no competing rivals.
The body length of dragonflies that we can see today is only 5 or 6 cm, while the body length of ancient dragonflies could reach 20 cm, and their wingspan could reach about one meter, much larger than modern dragonflies by tens of times.
Giant dragonflies also possessed extraordinary flying skills, being able to move quickly and adeptly among tree trunks. They could achieve a flying speed of nearly 65 km/h, making them the true rulers of the forest. The disaster caused by excessive oxygen levels The lush coniferous forests gradually formed thick layers of coal deposits over time, reaching tens of meters in thickness. These coal layers were present almost everywhere in the world and caused surface fires and underground coal fires.
The high oxygen environment has the characteristic of promoting the combustion process, which also accelerated the spread of the flames. Within a few months, the fire had spread over 2,000 km, and no animal could escape from the burning forest.
Over half a century later, the fire is still burning, and half of the Earth’s surface has been consumed by the raging flames, resulting in the extinction of many organisms. At the same time, the burning process also released a large amount of toxic gases, raising the average temperature at that time to nearly 6 degrees Celsius. As a result, the eggs of many amphibians and reptiles failed to hatch, leading to their extinction.
The toxic gases further increased the global temperature. Over a century after the fire outbreak, the average temperature rose to 32 degrees Celsius. Even after more than 1,500 years, the toxic gases emitted by the fire are still evaporating.
Thick smoke obscured the sunlight, and nearly half of the Earth’s surface was unable to see the Sun’s light. This also caused a significant amount of photosynthetic plants and organisms with poor respiratory function to die.
Therefore, if the oxygen levels on Earth were suddenly doubled, our planet could enter a “giant era” of insects and amphibians, but humans would suffer from diseases due to long-term exposure to an environment with high oxygen levels. Plants would grow rapidly, ultimately leading to global conflagration and causing the extinction of many species.