About the Philosopher's Stone
A random though unrelated to my previous posts has to do with one reason that we suppose that pre-historical civilizations did not exist is our inability to find evidence of mining that could be traced that far into the past. There is part of our mythology the concept of the Philosopher's Stone and in Hindu mythology the Cintamani. This stone is purported to have life giving benefits as well as the ability to transmute metals. There is a process which could "transmute" elements at room temperatures. The only problem is that we do not know how it works:

nice post
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I think alchemy is an intriguing subject and also find the idea of reasonably advanced civilisations to be interesting - Graham Hancock is a researcher who has written about this extensively.