Past just detecting a planet, transits allow for us to complete spectroscopy on starlight passing in the Earth’s environment. This means we can easily assess its composition—detecting gases like h2o vapor, methane, carbon dioxide, and possibly even oxygen. Priestley, on the other hand, referred to as oxygen "dephlogisticated air", and https://oxygenchambersnearme63062.blogminds.com/oxygen-chambers-for-dogs-no-further-a-mystery-33023005