We could detect oxygen in the atmosphere, which could indicate life, as oxygen will rapidly disappear from the atmosphere through oxidation without life resuppl

We could detect oxygen in the atmosphere, which could indicate life, as oxygen will rapidly disappear from the atmosphere through oxidation without life resupplying it. I don't think we have any built or planned telescopes that can detect oxygen 3000 light years away though. This article[1] discusses detecting oxygen in the atmosphere of exoplanets 5 pc away, about 16 light years, using the James Web space telescope that is yet to be launched. [1]: https://www.nature.com/articles/s41550-019-0977-7 https://www.nature.com/articles/s41550-019-0977-7