Both Earth and Mars currently have oxidising atmospheres, which is why iron-rich materials in daily life develop rust (a common name for iron oxide) during the oxidation reaction of iron and oxygen. The Earth has had an oxidising atmosphere for approximately 2.5 billion years, but before that, the atmosphere of this planet was reducing—there was no rust.
source https://phys.org/news/2021-02-planetary-scientists-evidence-atmosphere-ancient.html
