We know that on Earth, most life depends on oxygen, without the existence of oxygen life can not survive, even if scientists now look to space, in the search for extraterrestrial life, but also oxygen as a standard, then in the vast universe, is it possible that extraterrestrial life can survive without relying on oxygen?
Indeed, the conditions for life do not require oxygen to survive, taking our earth as an example, in the history of life evolution, there is one thing that many people may not know about, that is, the "great oxidation event" of the sudden increase in the free oxygen content of the atmosphere 2.6 billion years ago.
It should be known that as early as 3.8 billion years ago, the first primitive single-cell life was born on the earth, when the earth's atmospheric oxygen content was very small, accounting for only 0.02%, so the original primitive earth life was actually anaerobic organisms.
It wasn't until 400 million years later, when a creature called cyanobacteria appeared on Earth, and everything began to change.
Cyanobacteria are oxygen-producing single-cell prokaryotes that use sunlight for photosynthesis and then suck in carbon dioxide to release oxygen. So far, after a long period of 1 billion years of evolution, the entire Earth's atmosphere has developed from a near-anaerobic state to an aerobic state, and the earth's atmospheric oxygen content has soared from the original 0.02% to 4%.
As a result, the oxygen content increased, resulting in a large number of anaerobic organisms in the ocean, almost all of which were killed by oxygen. Eventually, the remaining organisms gradually accepted oxygen and evolved more complex life forms in an aerobic environment, so much so that most life on Earth today depends on oxygen
Therefore, living things on Earth are not born to need oxygen, so when looking for extraterrestrial life, we do not have to follow oxygen as a standard, if we look for extraterrestrial life from the perspective of anaerobic organisms, it may be a good idea. After all, under different environmental conditions, it is entirely possible to evolve into different forms of life!
In fact, as early as 1891, Julius Schönner, an astrophysicist at the University of Potsdam, proposed a life form that did not require oxygen, that is, silicon-based life. Silicon-based life is simply a life composed of silicon compounds, which is more tenacious than carbon-based life, such as in the science fiction movie Transformers, the life on the planet Cybertron is silicon-based life, and their living environment can be a "death star" with high concentrations of carbon dioxide at high temperature and pressure.
It's just that it is very difficult to detect silicon-based life in the vast universe, and according to scientists, the possibility of silicon-based life is also very slim, so at present, human beings are starting in the direction of oxygen and liquid water to find the same carbon base as us. Because Earth is the only planet known to mankind to have life! The probability of finding it is more likely than other life forms!
But then again, the level of human science and technology is still very backward, and it is impossible to observe distant exoplanets at close range, so we still have a long way to go to really find extraterrestrial life!