Newly discovered biomarker signatures point to a whole range of previously unknown organisms that dominated complex life on Earth about a billion years ago. They differed from complex eukaryotic life as we know it, such as animals, plants, and algae in their cell structure and likely metabolism, which was adapted to a world that had far less oxygen in the atmosphere than today. An international team of researchers, including GFZ geochemist Christian Hallmann, now reports on this breakthrough for the field of evolutionary geobiology in the journal Nature.
‘Shadow biosphere’ is another term for it. Here’s a brief primer on the possibility: https://earthsky.org/earth/invisible-alien-life-exist-among-us-silicon-based/
It’s tempting from a worldbuilding standpoint to extrapolate from that to a full-fledged parallel civilization just out of phase with ours.
Yeah, that’s absolutely happening in the current world I’m working on (for a TTRPG). That’s too fun to pass up and introduces all kinds of gameplay possibilities. Thanks for the additional info!