How important is oxygen to us? Almost all living things, including humans, need oxygen to survive. We may be able to last a week without eating or drinking, but if there is no oxygen, it may not exceed 5 minutes.
Maybe you don’t know, 4 billion years ago, when life first appeared on the earth, they didn’t need oxygen, and oxygen was for them , Is the out-and-out poison gas.
How does oxygen appear, and how does life become dependent on oxygen? This time we will talk about a major event in the history of life development, the Great Oxidation Event. The major oxidation event caused a rapid increase in the oxygen content of the earth’s atmosphere, and at the same time the dominant life forms on the earth changed from anaerobic organisms to aerobic organisms.
Actually, there have been two major oxidation events in history. The first time was the process of oxygen from scratch, and the second time was the process of rapid increase in oxygen content. Each time, a new object that is 1 million times larger than the original creature is produced.
Today, let’s focus on the first major oxidation event.
About 4 billion years ago, life appeared on the earth. What kind of environment was it at that time, by current standards, it was simply hell. Continuous volcanic eruptions, frequent collisions with extraterrestrial bodies, continuous formation and evaporation of primitive oceans, the air is full of carbon dioxide, nitrogen, methane, hydrogen sulfide, water vapor, and a small amount of hydrogen.
At this time, there is no free oxygen at all. Life is produced under such conditions, and they can survive without oxygen. These life, we call them prokaryotes, compared with most living things today-eukaryotes-they have no nucleus, simpler and more primitive, and their energy efficiency is much lower than that of eukaryotes.
However, about 2.4 billion years ago, the oxygen content in the air began to increase, from about 0.02% to about 2~4%, the whole process lasted about 600 million years . The oxygen content in the air today is 21%. After the Great Oxidation Event, the oxygen content was actually not high, only 1/10 of the current level, but just such a small amount of oxygen caused earth-shaking changes. This led to the death of almost all anaerobic organisms at that time, and the surviving organisms developed the ability to resist and use oxygen, and continued to grow until the world today is formed.
The reason for the production of oxygen is relatively clear. At that time, there appeared a kind of organism that can provide energy for itself through photosynthesis. It releases oxygen during photosynthesis. This kind of organism is cyanobacteria.
But according to fossil studies, cyanobacteria appeared before the major oxidation event, which is about 2.7 billion years ago, with an interval of 300 million years, so why did the oxygen content not increase in such a long time? ? Where did all the produced oxygen go? There must be some reason that prevented the increase in oxygen content.
cyanobacteria
After decades of research, scientists found that volcanic eruptions played a key role in this.
Since 2.7 billion years ago, the earth has gradually cooled, the volcanic eruption has weakened, and the nickel released by the volcanic eruption has begun to decline. What's the use of nickel? It plays a key role in a bacteria that destroys oxygen. This kind of bacteria is called methanogens. Both methanogens and cyanobacteria live in the primitive ocean. They are in a competitive relationship, and methanogens have always been dominant. Cyanobacteria produce oxygen, and methanogens produce methane. As a result, when methane encounters oxygen, carbon dioxide is produced, and oxygen disappears.
Methanogens rely heavily on nickel for survival, and a metabolic enzyme used to produce methane requires nickel. Once nickel starts to decrease, methanogens will die, then methane production will decrease, oxygen destruction will decrease, oxygen-producing microorganisms will increase, and the final result will be an increase in oxygen content.
Smith Methanogen
This is not over yet, because methane is a greenhouse gas, its greenhouse effect is 23 times that of carbon dioxide. The reduction of methane led to a reduction in the greenhouse effect and a drop in the earth's temperature. As a result, another geological event was accompanied by a major oxidation event: the Huron Ice Age, which lasted 300 million years.
Under the double blow of nickel deficiency and low temperature, anaerobic organisms have almost disappeared.
In addition, a recent study found that a volcanic eruption will eject a large amount of earth's internal material onto the earth's surface, such as lava, rocks and gas. Because they have been in an oxygen-deficient environment, these rocks and gases are in a reduced state, and they are very easy to combine with oxygen. Frequent volcanic eruptions continuously replenish reducing substances to consume oxygen.
As the earth gradually cooled, volcanic activity weakened, and the release of reducing substances gradually decreased. It finally reached the critical point about 2.4 billion years ago. Oxygen finally prevailed and began to gradually accumulate in the atmosphere.
Therefore, the Great Oxidation Event is a turning point in the evolution of life on Earth. From then on, lucky eukaryotes began to dominate until today.
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