A group of researchers from the University of California has managed to develop a method for understanding the evolution of the atmosphere millions of years ago. To date there was no method to know the amounts of oxygen and ozone in the atmosphere and the evolution of both. This team of researchers has analyzed the rocks between 3,900 and 2,200 million years old, analyzing the traces of reactions between sulfur and oxygen, which are of the changes that occurred in the atmosphere. Between 2,500 and 2,100 million years ago there were strong changes in the Earth's atmosphere due to the accumulation of oxygen and ozone. This period was very important for the evolution of life and knowing the characteristics of the atmosphere then is very interesting for current researchers.