A topic that sparked my interest this quarter was the chemical composition of the Earth's atmosphere before the evolution of oxygen creating cyanobacteria. As stated in lecture, scientists already know that the early Earth's atmosphere was reducing. What does it mean to have a reducing atmosphere? To have a reducing atmosphere means the lack of any prominent oxidizers such as oxygen. During the Hadean period, approximately 4.5 billion years ago, there was no presence of free oxygen. However, scientists do know that during this period the atmosphere was composed of mainly hydrogen sulfide, methane, ammonia, incredibly high amounts of carbon dioxide, and even small amounts of water vapor.
How do scientists know this? How could scientists figure out the main components of our atmophere from 4.5 billion years ago? These questions lead me to do some research and I came across a lab that used the oxidation rates of chromate, zircon, vanadium or igenous rock to provide evidence of early Earth's composition.
If you are interested in learning about these labs and their techniques, there is a link provided below.