How did the earth's atmosphere change to become today's nitrogen and oxygen atmosphere?

Answer 1

There was an Ice age on the Earth 2.4 billion years ago that lasted tens of millions of years, which marks as the longest lasting Ice Age on the Earth. After the Ice Age was over, the Earth was fully covered with Ice. And this Ice means, pure Ice, no snow or no water in it; which also comes to a meaning that it is Iced Gas. The Freeze of the Weather is so cold that it Froze the entire Gas on the Earth, which Gas was the remnant from the Galactic Creation of the Earth's occurrence(from Gas Dust). When this Ice of Frozen Gas has started to melt down due to change of seasons --in Physics if you have a frozen object, and if you want to melt it with the fastest way possible, you not only need to heat it, you also need to cool it every once in a while stopping the heating and start cooling, and then stopping the cooling and start heating again, to fasten the process of melting--. As the Earth turns around the Sun, the seasons changed for tens of millions of years, and not only the Iced Gas is melted, but through the Sun Rays and Radioactive Energy that came from the Sun, the Iced Gas is melted to evaporating water that contained Nitrogen and Oxygen and so many other gases that made it possible to breathe and live under an atmosphere.

From that perspective, one day if humankind wants to explore a life in Space in other planets of other galaxies, or wants to create a man-made atmosphere, the amount of energy and time is so much more larger and longer than one can ever think. Consider hundreds of millions of years to continuously freeze and heat a Galactic planet, in order to produce an evaporating water on the ground so that it will cover the sky of this planet to come to life as an atmosphere. For human technology, to be able to find and manipulate this kind of energy is not possible, as you see.

Answer 2

The Earth's early atmosphere was primarily composed of gases like carbon dioxide, water vapor, and nitrogen. Over time, volcanic activity released more gases into the atmosphere, which led to a buildup of nitrogen and oxygen. Additionally, the emergence of photosynthetic organisms like cyanobacteria and plants played a crucial role in producing oxygen through photosynthesis, leading to the nitrogen and oxygen-rich atmosphere we have today.