Jay Kaufman said that while scientists cannot collect and study samples of the ancient atmosphere, they can "collect rocks that were formed ... under that atmosphere." Why are scientists able to learn about the ancient atmosphere by studying the rocks that came into contact with the ancient atmosphere?

The scientists are able to get information from the rocks about the ancient atmosphere because the rocks have been in contact with it. By being in contact with the atmosphere, the rocks manage to get the gases from their atmosphere into their structure. Some rocks are better in providing this evidence than others, as it depends on how much a rock has been exposed to the atmosphere, as well as its structure, but still they have at least certain amount of elements that are good indicators about the composition of the ancient atmosphere, and to what kind of environment it was contributing.