Silurian hypothesis

[Leviset]

See this Paper from Fermat’s Library
https://fermatslibrary.com/s/the-siluria...cal-record


I’ve pondered this ‘possibility’ all my length - that there have been civilisation(s) before us on Earth and that for some reason they became extinct and also that any possible archaeological evidence has long degraded and disappeared. However the paper also looks at possible civilisations from Venus or Mars. What I’ve NEVER seen discussed is why do we only look for intelligent(?) life like our own that breathes oxygen? Could there not be lifeforms that evolved that could survive on planets that needed obnoxious elements (cf to us) like Sulphur, CO2, N etc. Lifeforms that could exist under atmospheric pressures that would crush us.