Our luck on earth.

The Earth's atmosphere is rich in oxygen, it is the second largest gas after nitrogen with 78 percent, which played an important role in the development of life. Obviously oxygen is also very important in the atmospheric composition with almost 21 percent of the total and it is the gas that we need to breathe, it is needed by humans, but also by animals and many living beings. But so much oxygen on a planet in one atmosphere is something rare, in fact, we have not found it on other worlds, our neighbors have a very different atmosphere, Venus has an atmosphere basically of CO2 or carbon dioxide up to 96.5 percent and 3.5 percent of that atmosphere is nitrogen, Mars although its atmosphere is much thinner than that of Venus, because among other things to retain atmosphere it is necessary to have gravity and Mars is smaller despite having a much less dense atmosphere it is which has a very similar composition, it has a percentage of carbon dioxide of 95.3% and nitrogen of 2.7%. This is very curious, two very different planets.

The earth had an atmosphere rich in carbon dioxide and without oxygen and it did for about 2 billion years. If we had a time machine and we traveled 4 billion years ago we would have to wear a gas mask, because otherwise we would die from lack of oxygen, in fact, life on earth arose with that type of atmosphere, without oxygen, Luca, the first living being from which we all descend and was born on that earth of carbon dioxide, basically it was a life that was found in the sea and This makes us deduce that it is possible that all rocky planets such as Venus, Mars or Earth and all the rest of the rocky planets that exist in the universe have at least similar atmospheres rich in CO2. Yes, CO2 is a greenhouse gas, and the earth was not a scorching hell, because in those early times the Sun was colder, the Sun increases its brightness and heat at a rate of 10% every 1000 million years, so the CO2-rich atmosphere of the primitive earth was very good, because it allowed pleasant temperatures, bacteria and microorganisms thrived, there were even photosynthetic organisms, that is, they carried out anoxygenic photosynthesis, this means that they used the energy of the Sun in photosynthesis, but it was a type of photosynthesis that did not produce oxygen, as is happening right now with algae or plants.

The existence of life on Earth depends on certain changes that occurred at certain moments that were opportune moments. That Earth was the paradise of bacteria, but it was not going to last forever because with the constant increase in sunlight, the Earth would receiving more and more energy and with an atmosphere rich in CO2 it retained more and more heat, at first it was fine because well the sun was colder and so with that atmosphere and greenhouse effect we had pleasant temperatures but with the passage of time that was going to ending badly was going to end up triggering a catastrophic greenhouse effect that would end up transforming the earth into a new Venus. Maybe that's what happened to Venus billions of years ago, a little earlier than what would have happened to the Earth since it is a little closer to the sun than the Earth, but the Earth would have been exactly the same thing happened, if it weren't for the fact that something revolutionary happened, something strange, something that we don't know how to explain, something that also meant a catastrophe, a catastrophe with the extinction of many forms of life about 2,800 million years ago, the first organisms appeared capable of carry out oxygenic photosynthesis, the one we know, from algae, from plants, that type of photosynthesis also obtained energy from the sun but in the process it produced oxygen, we do not know why this evolution occurred, but it was crucial, it was not a quick event. It is estimated that the process that ended up oxygenating the Earth's atmosphere took at least 400 million years, but it was at the right time, with the result that a large part of the previous life forms were exterminated and there was a radical change in the earth's atmosphere, the new oxygen reacted by eliminating greenhouse gases and cooling the earth, as I already said, at an opportune moment, since the previous atmospheric position was certain to have transformed the earth into a new Venus.