How long can the oxygen on earth last?

How is oxygen on the earth formed?

  The earth has a history of 4.6 billion years. In the early days of the earth, the oxygen content in the atmosphere was extremely scarce, only a few tenths of a percent, which was basically negligible, and most of it was carbon dioxide and nitrogen. Starting about 2.5 billion years ago, the first “Great Oxidation Event” occurred in the Earth’s atmosphere. Single-celled organisms such as cyanobacteria living in primitive oceans and other waters started this event. They can use sunlight for photosynthesis and produce oxygen, and the oxygen content on the earth has gradually increased.
  About 600 million years ago, the oxygen content on the earth reached about 1%. At this time, the second “Great Oxidation Event” occurred on the earth. The earth’s ocean area is large and the temperature is suitable, which is very suitable for the growth of cyanobacteria. The large-scale emergence of cyanobacteria in waters such as the earth’s oceans has doubled the oxygen concentration in the oceans, and the oxygen in the seawater enters the atmosphere through gas exchange, and the oxygen content in the atmosphere also increases rapidly. The number of animals and plants on the earth’s land has also begun to increase, and the emergence of plants in large numbers has doubled the increase in oxygen. By the Carboniferous, about 300 million years ago, the oxygen content on the earth once reached about 35%.
  Every time there is a mass extinction, the concentration of oxygen on the earth will decrease. When the oxygen content was around 21%, mankind was born. Today, humans and other animals have fully adapted to such an environment. When the oxygen concentration on the earth is lower than 19.5%, it is an oxygen-deficient state, and when the oxygen concentration is higher than 23.6%, it is an oxygen-rich state, which will affect the human body.
Will the oxygen on the earth run out?

  As early as 100 years ago, some people were worried about the increase in carbon dioxide content. In 1898, the British physicist Kelvin pointed out: With the development of industry and the increase of population, this situation is very worrying. After 500 years, all oxygen on the earth will be consumed, leaving only an increasing amount of carbon dioxide.
  However, most people believe that there is no need to worry about oxygen being depleted. The main reason is that there are many kinds of green plants growing on the earth. A large number of green plants in the world will absorb a large amount of carbon dioxide during photosynthesis, and at the same time emit oxygen. Plants absorb sunlight, water, and carbon dioxide exhaled by other organisms, and release oxygen, which is absorbed and used by other organisms.
  According to scientific experiment analysis, the carbon dioxide absorbed by 3 large eucalyptus trees is equivalent to the amount of carbon dioxide that a person exhales every day. In addition to green plants consuming carbon dioxide, scientists have also found that under the action of carbon dioxide and water, the calcium carbonate contained in the rock will turn into acid calcium carbonate. This form of calcium carbonate can be dissolved in water. According to analysis, the weathering of rocks consumes about 4 billion to 7 billion tons of carbon dioxide each year. These weathered rocks are combined with calcification to re-form limestone along with rivers and seas, and sink to the bottom of the sea in the form of new rocks.
  In order to study how the earth’s atmosphere will evolve, not long ago, Japanese scientist Ozaki Kazumi and American scientist Reinhard jointly established an earth system model that simulates the earth’s climate and biochemical processes. Because of the uncertainty in the development of these processes, scientists have adopted a stochastic approach to make a probabilistic assessment of the lifetime of the oxygen-enriched atmosphere. The two scientists performed more than 400,000 operations to change the parameters of the model, and found that the current state of the oxygen-rich atmosphere on the earth may continue for 1 billion years, and then the rapid deoxygenation will return the earth’s atmosphere to something similar to 2.5 billion years ago. The early state before the “Great Oxidation Event”. Therefore, experts pointed out that the conclusion drawn by this model is: at least one thing is already clear, nothing is eternal, and the oxygen on earth is no exception.
What happens if the oxygen concentration decreases?

  What will happen if the concentration of oxygen on the earth decreases in the future? First of all, humans may become smaller in size, and their height may also become shorter as the oxygen concentration decreases. This is mainly because if the oxygen content is reduced, the human respiratory system will also be adjusted accordingly. The reduced oxygen intake of the respiratory system will naturally affect the human body. Not only will the human body become shorter, but the body may not be as strong as it is now. Not only humans, but also other animals. If the earth’s atmosphere becomes thinner, it will limit the survival of animals, and of course, the number of humans will also decrease.