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While oxygen is crucial for most living organisms, its composition in the atmosphere is relatively low, around 21%. Does higher oxygen mean better for life on Earth? How would the Earth be affected if the oxygen levels suddenly doubled?
Where does the oxygen on Earth come from?
Earth has existed for 4.6 billion years. After the Big Bang, it initially formed as a constantly burning 'fiery ball,' cooling after 1.1 billion years, allowing the emergence of life and the gradual formation of the atmosphere.
In the early atmosphere, oxygen was absent, filled with gases like ammonia and methane. Oxygen in the atmosphere primarily originated from two sources: photosynthesis by plants and non-biological processes during the water photolysis.
Today, we know that the oxygen levels in the air are about 21%, crucial for humans and other organisms. In an oxygen-deficient environment, humans cannot breathe normally.
What happens if the Earth's oxygen suddenly doubles - reaching around 40% in the air?
How do humans feel with varying levels of oxygen in the air?
At 0% to 10% oxygen, breathing becomes difficult, blood oxygen levels continuously drop, leading to loss of alertness, confusion, and eventually death due to oxygen deficiency.
At 10% to 16% oxygen, humans also experience difficulty breathing, chest pain, and even cardiac arrest.
At 15% to 19% oxygen, individuals may experience visual disturbances, dizziness, difficulty concentrating on tasks, and studying.
At 19% to 24% oxygen, within the normal air oxygen concentration range, humans can live, study, exercise, and rest normally.
At 24% to 31% oxygen levels, the environment is rich in oxygen, the most suitable for human habitation. People feel alert, energetic, and experience improved sleep.
With oxygen levels from 31% to 52%, higher oxygen concentrations accelerate aging, reduce lifespan, and increase susceptibility to diseases such as lung inflammation and macular degeneration due to oxygen.
From 52% to 90% oxygen levels, individuals may feel dizzy initially, gradually adapting, but eventually succumb to oxygen toxicity and die from respiratory failure.
At 90% to 100% oxygen levels, oxidation occurs rapidly, leading to immediate fatality.
If Earth's oxygen levels only double, the corresponding environment would range from 31% to 52% oxygen. Although the human body may adapt slowly, unforeseeable damages over time are inevitable.
Earth has experienced a high-oxygen environment in the past.
In reality, Earth once had a super-oxygen environment with an oxygen level of 40%.
Over 300 million years ago, at the end of the Carboniferous period, Earth's environment was vastly different. The continents were fused into a massive landmass called Pangea by scientists.
The emergence of lignin gave rise to a plethora of tall, majestic plants. True trees appeared, and needle-leaved trees covered the land. Through photosynthesis, plants absorbed carbon dioxide and released oxygen, leading to an atmosphere with an oxygen concentration of up to 45% at that time, precisely double the current levels.
Excess oxygen levels gave rise to gigantic insects and amphibians.
The terrestrial rulers of the late Carboniferous weren't dinosaurs but rather giant insects and amphibians. The high oxygen levels in the late Carboniferous also fueled the evolution of insects.
Although amphibian eggs lacked a hard shell and occasionally required water immersion, they evolved to large sizes due to a lack of competitive adversaries.
Dragonflies we see today have a body length of only 5 or 6 cm, while their prehistoric counterparts could reach up to 20 cm in body length with wingspans of about one meter, several times larger than modern dragonflies.
Giant dragonflies possessed extraordinary flying skills, swiftly maneuvering between tree trunks at speeds nearing 65 km/h, truly ruling the forest.
The catastrophe arising from excessively high oxygen levels
Lush pine forests gradually formed thick coal layers, accumulating over time. These coal layers were widespread worldwide, causing surface and underground coal fires.
High oxygen environments support rapid combustion, escalating the spread of flames. Within months, the fire extended over 2,000 km, leaving no creature able to escape the raging forest.
Over half a century later, the relentless flames continued, consuming half the Earth's surface, leading to the extinction of many species. The combustion process released a large amount of toxic gases, raising the average temperature by nearly 6 degrees Celsius. The eggs of numerous amphibians and reptiles failed to hatch, resulting in their extinction.
Toxic gases escalated global temperatures. Over a century after the fiery outbreak, the average temperature soared to 32 degrees Celsius. Even after more than 1,500 years, the toxic fumes from the blaze still linger.
Dense dust obscured the Sun, rendering nearly half the Earth in perpetual darkness. This led to the death of numerous photosynthetic plants and organisms with impaired respiratory functions.
Therefore, if Earth's oxygen levels were to suddenly double, our planet might enter an 'age of giants' for insects and amphibians, but humans would suffer from prolonged exposure to a high-oxygen environment. Rapid plant growth would ensue, ultimately leading to global wildfires and causing widespread extinction.
