Why is it difficult to be precise about the composition of the earths early atmosphere?

It is challenging to be precise about the composition of Earth's early atmosphere because there is limited direct evidence available from that time period. The composition of ancient atmospheres is inferred from indirect sources like ancient rocks, minerals, and fossilized remains, which can give us clues but not a complete picture. Additionally, the Earth has undergone significant changes over billions of years, further complicating efforts to accurately reconstruct the exact composition of the early atmosphere.