Why do scientists use oxygen as the basis for finding life, can aliens breathe hydrogen?

This question is very interesting and representative. There are several problems hidden in it. Let me take a look at it and explain it one by one!

Is oxygen a condition for life to exist?

Many people understand that oxygen is an essential ingredient for human survival, so "scientists believe that a planet must have oxygen to breed life, and oxygen is a prerequisite for life."

In fact, this is a huge misunderstanding, oxygen is not a prerequisite for life, but a great feat of life. That is to say, only planets with life are likely to have a large amount of oxygen, and planets without life have different compositions, but it is absolutely impossible to have a large amount of oxygen.

Why? In junior high school chemistry, we learned two words - "oxidizing agent" and "reducing agent". To review, in fact, their characteristic is that the electron orbital of the oxidant is devoid of electrons and they will strongly attract electrons to fill up; the reducing agent is the exact opposite, and the electrons appear to be somewhat "excessive". Such two elements are likely to reach a "consensus" to form a compound, and the electronic relationship between them is a type of chemical bond.

You see, this characteristic is called "oxidativeness", which means that oxygen has a very prominent performance in this aspect. Although oxygen is not the strongest oxidant, it is already strong enough that it will "strongly rob" almost most elements. The electrons, which are chemically called "active waves", are very strong.

Therefore, in the absence of life intervention, oxygen will almost always form compounds with other elements, and it is impossible to exist in the form of elemental substances. The atmosphere of the primitive earth is full of carbon dioxide, methane, nitrogen and a small amount of ammonia.

Who produces Earth's oxygen?

So, where did the Earth's oxygen come from? Yes, as you know above, after the evolution of photosynthesis, cyanobacteria reduced the abundance of oxygen in Earth's seas and skies. This historical process, known as the "Great Oxidation Event," occurred about 2.2 billion years ago.

We often worry about the destruction of nature by humans, but in fact the earliest events that drastically and completely changed the appearance of the earth were done by bacteria. This is the first time life has learned to use the energy of sunlight to fix carbon dioxide from the air. Down, and then the bodies of these bacteria sank to the seabed and the bottom of the lake, and entered the lithosphere of the earth with the geological movement.

Every carbon atom buried in the ground corresponds to one oxygen molecule in the atmosphere. This huge amount can be described as extremely astonishing. Now all the carbon in the earth's ecosystem adds up to only about 1/26,000 of that buried in the ground! And fossil fuels only account for a very small part of it, and most of the carbon is dispersed in the shale in tiny particles, in a form that is almost unusable by humans.

At the beginning, the released oxygen will react with various reducing molecules on the surface of the earth and combine with iron, sulfur, and methane, but it has to be said that the power of bacteria is too powerful, and there was so much oxygen that eventually all the iron, sulfur, and methane were oxidized, and after there was nothing left to oxidize, a lot of oxygen poured into the atmosphere, turning the Earth into an oxygen-rich planet.

The significance of oxygen is not only that, if the discovery of the existence of oxygen can prove that life already exists on this planet, it can also reveal some other exciting news.

The world has changed since there was oxygen.

•  The planet could keep its own ocean.

Mars was once a planet with oceans. Human probes have found that there are a lot of pebbles on its surface. This is a trace that can only appear after a long flow of water. Venus may have been the same. After all, we were all born in the same nebula. It won't be much different.

But why is Mars so desolate and lonely now? Because it loses all the water, the high-energy rays in the sunlight will split the water and turn it into hydrogen and oxygen. Hydrogen is very frivolous and can easily escape into space. In the end, the water will be decomposed cleanly, and the oxygen will react with the reducing substances on the surface. It is for this reason that the surface of Mars is covered with red iron oxide, making it so red.

After having a lot of oxygen, the hydrogen atoms will be oxidized before they can escape, and they will become water and return to the earth again.

•  organisms have the basic conditions for advanced evolution.

Anaerobic respiration can only release about 10% of the energy of energy-supplying substances, while aerobic respiration can release about 40% of the energy. The four-digit efficiency improvement brings about the ability to support complex food chains and ecological levels. Originally, it could only support Two to three levels of nutrition can support about six or more levels when oxygen is involved. Only then will more complex ecosystems and greater diversity of life emerge.

Let's start with mainstream oxygen!

Therefore, oxygen gas is indispensable both as evidence of the existence of life and as a condition for the advancement of life. Oxygen is a relatively abundant element in our universe. If we don’t look for traces of life related to oxygen, other evidence will be like finding the needle in the haystack and finding the moon in the water.