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About 2.5 billion years ago, life on Earth suffered a catastrophe, and an alien creature on a spacecraft once said something thought-provoking: "Your oxygen is toxic to us!"
In fact, our oxygen has killed millions of creatures before that.
The phrase "your oxygen is poisonous to us" is not an empty phrase, and oxygen is also a deadly poison gas for most living beings on the earth, including us humans.
Why this strange phenomenon?
Most people take the so-called "oxygen" for granted as a good thing, so why does it have "deadly gas"?
In the final analysis, it is because this thing called "oxygen" by humans is not an innate thing, but is produced by the accumulation of living things over countless generations.
And finally one day, the biomass that can be used to produce oxygen through photosynthesis will surge, and a large amount of "toxic substances" containing huge amounts of energy will be erupted into the air, which is the mass lethal force brought about by mass extinction events - ultraviolet rays that modern people often encounter.
The vast majority of organic matter is decomposed by ultraviolet light, including important proteins, nucleic acids and lipids in almost all living organisms inside and outside the body.
Therefore, the "deadly gas" brought about by this mass extinction event will cause most organisms to be vulnerable and killed on a large scale, which has triggered the large-scale evolution of life on earth.
It is the main body of the "poisonous substance" called "oxygen" by humans - carbon dioxide, and the toxicity of the "deadly gas" brought about by this mass extinction event is ultraviolet rays, which also directly leads to the unique history of human extinction.
1. The source of oxygen on Earth.
To understand whether "oxygen" is really a "toxic gas", we must first understand what the term "oxygen" really means.
Oxygen literally refers to elemental oxygen O2, and the "oxygen" that people often say in daily life also refers to the oxygen molecule O2.
In chemistry, elemental oxygen O is a strong oxidizing agent, which literally means that it can oxidize with many substances and release energy.
Another point is that when we say "oxygen", we mean that from the perspective of the earth's atmosphere, oxygen O2 molecules account for the majority of the proportion, and "oxygen" also includes another oxygen O3 called "ozone", which accounts for a very small proportion of the earth's atmosphere.
The ozone O3 molecule is made up of three oxygen atoms, and compared to elemental oxygen O2, ozone O3 is not stable in the air, decomposes under certain conditions, releases some energy, and undergoes chemical reactions that "clean" and "damage" proteins.
Therefore, ozone O3 is also a "potentially toxic" oxidant, which provides favorable evidence for other organisms to claim that oxygen is a toxic gas.
However, the so-called "oxygen is a toxic gas" is ultimately untenable.
Although oxygen in living bodies is a toxic molecular oxygen that is highly reactive to living beings, all other properties prove that oxygen should not be considered a "toxic gas".
First of all, the O atom as oxygen is an extremely active element, it is very easy to combine with other atoms to form compounds, and most of the organic matter on the earth is composed of carbon and oxygen, nitrogen, hydrogen, sulfur and other atoms, oxygen is one of the most important "raw materials".
It is oxygen that enables living beings on Earth to combine these atoms into biological macromolecules, which are essential for all living things.
In addition, oxygen is also the source of energy that most organisms use to maintain respiration, which breaks down the organic matter that is conveyed to the cells and releases energy, a process called "oxidation".
Therefore, we can say that it is oxygen O that allows the soul of the earth to possess and become a talent-based planet.
Let's look at the activity of "oxygen" O2 compared to elemental oxygen O, because O2 is composed of two O atoms, so it is not as active as elemental oxygen, it will not react with anything "too actively", and it can even exist stably for more than 200 million years.
Therefore, we can also say that it is the presence of oxygen in the atmosphere that makes the Earth a vibrant planet.
On both counts, it would be a mistake if organisms did not consider O2 to be a hazard.
So where does the saying that "oxygen is a toxic gas" come from?
This statement ultimately goes back to the earth before the origin of life, because there was no oxygen in the earth's atmosphere before the pre-oxidation event, which means that life on earth must live on anaerobic metabolism.
Although different organisms are metabolized differently, they all obtain energy by oxidizing organic matter.
In other words, before the great oxidation event on Earth, there were no products of "oxidation" in living organisms, so organisms on Earth could not use oxygen at all, nor did they have enzymes to adapt to oxygen, and oxygen was a toxic "mysterious substance" for them at that time.
Second, the great oxidation event.
Life on Earth is so diverse, but all living things use the same source of energy, in fact, because the large-scale organisms are a type of cyanobacteria in oxygen.
These cyanobacteria used photosynthesis to produce oxygen, which ultimately led to the dominance of oxygen in the Earth's atmosphere.
In fact, before the emergence of cyanobacteria, there was no oxygen in the earth's atmosphere, and hundreds of millions of years later, because oxygen is a gas that can form ozone or react with organic matter, the large oxidation event also means that a large amount of polymer organic matter will be consumed by oxygen, and then organisms will release carbon dioxide while consuming a large amount of oxygen, so the large oxidation event is a long, multi-million year process.
On the other hand, because ozone decomposes when sunlight is intense, the largest ozone layer in Earth's history was in the Cambrian period, about 400 million years ago.
Today, El Niño is very common, and in the Cambrian period, El Niño was almost non-existent due to the rarity of extreme weather conditions on Earth.
In other words, during the Cambrian period, the climate in Antarctica was extremely cold, there were no greenhouse gases, and there was a massive glaciation of the ground, which made it impossible to consume the large amount of carbon dioxide that erupted.
In addition, the sedimentation of the massive paleocontinental basins of the time also buried a large amount of organic matter, and these geological processes almost did not bury oxygen, so the oxygen on Earth increased dramatically, and eventually formed an atmosphere with almost the same oxygen content as it does today.
Moreover, 250 million years ago, there was an extinction event on the earth, and the astronauts who came here also found that the earth's civilization was very backward, and even insulted the earth's civilization as a "living planet".
Life on Earth suffered a cataclysm 2.5 billion years ago, when oxygen led to the mass extinction, when life that lived by anaerobic metabolism disappeared in large numbers and organisms that could react with oxygen died out in large numbers.
However, oxygen is a toxic substance after the great oxidation event, although the anaerobic metabolism of oxygen has disappeared explosively, but the biodiversity is still very high, and the new life forms have killed a large number of old life forms through the toxicity of oxygen, and the phoenix nirvana, life has gradually recovered its former glory.
3. Formation of the ozone layer.
In addition to the fact that ultraviolet rays are an extremely dangerous external threat, life on other planets is also not resistant to it, which is why interstellar astronauts spit on Earth civilization so much.
Fortunately, there is a "protective umbrella" on Earth that protects life on Earth, and it is the layer that humans call the ozone layer.
The ozone layer is a thin, energetic layer, which is mainly composed of ozone molecule O3, and ozone can absorb ultraviolet rays, weaken or prevent ultraviolet rays from reaching the earth's surface, and is the basis of biological activities on the earth.
However, it is precisely because the ozone layer is unstable that there is an unstable ozone sphere.
The most prominent phenomenon of ozone layer instability is the ozone hole in Antarctica, every time the summer in Antarctica ends, the local climate is very suitable for the generation of ozone holes, the ozone hole will begin to expand, until the end of the season, the ozone hole will slowly disappear on its own.
In the Arctic, the local climate is not as suitable for the ozone hole as in the Antarctic region, so the ozone hole produced in the Arctic is generally small and disappears on its own after the sun rises.
In the 70s of the 20th century, human scientists discovered that the ozone hole over the Antarctic was expanding, and in addition to discovering that the Arctic region could also produce an ozone hole under certain conditions, which made people finally realize the impact of chlorofluorocarbons in the earth's atmosphere on the ozone layer.
Since the ozone layer in the Earth's atmosphere is very thin and CFCs have a stable cycle of biodegradation, it was immediately decided to ban their continued emissions when they were found to be harmful.
Today, the earth's atmosphere has been stabilized by the increase in oxygen caused by the great oxidation event, and human beings have made great efforts to protect the environment.
Although unstable ozone holes still occur from time to time, they are not harmful to life on Earth.
However, in the 21st century, scientists have discovered that the Earth's polar climate has increased unprecedentedly, and the massive melting of glaciers in the Antarctic region has further expanded the danger of the ozone hole, and the Earth's climate has also changed dramatically.
epilogue
In order to avoid the tragedy of repeating the Great Oxidation Event, scientists speculate that almost all life forms are extinct, and that only extreme anaerobic organisms in the deep sea have survived, and are the only ones on Earth.
Scientists speculate that the Great Oxidation Event is caused by supernova explosions, volcanic eruptions, or other extraterrestrial events that destroy the ozone layer and cause an excess of oxygen, which is why life begins to adapt to oxygen.
Now, the hole in the ozone layer over the Antarctic and the Arctic has made scientists on Earth eager to know if similar problems exist in other parts of the planet.
Therefore, human beings should strengthen environmental protection and reduce harmful gas emissions to protect the ozone layer and life on earth.