When thinking about why we have not encountered intelligent aliens yet, as Adam Kirsch does (The long read, 11 August), it seems to me that one factor gets neglected: fossil fuels. Alien life could develop intelligence on myriad planets, but to develop advanced technology that would enable them to get off‑world, they need to go through an equivalent of the Industrial Revolution, and that needed first coal, then oil and gas.
There could be many intelligent alien races out there, but on planets without an easily accessible fossil fuel equivalent, they’d never get past a 17th-century level of development.
