https://thenextweb.com/syndication/2020/05/05/why-our-search-for-aliens-should-focus-on-hydrogen-rich-planets/

The first time we find evidence of life on a planet orbiting another star (an exoplanet), it is probably going to be by analysing the gases in its atmosphere. With the number of known Earth-like planets growing, we could soon discover gases in an exoplanet’s atmosphere that are associated with life on Earth.

But what if alien life uses somewhat different chemistry to ours? A new study, published in Nature Astronomy, argues that our best chances of using atmospheres to find evidence of life is to broaden our search from focusing on planets like our own to include those with a hydrogen atmosphere.