In Feynman Lectures on Physics Volume I, Feynman talks about the relation between Physics and Geology. He says “Mountains are no lower today, on the average, than they were in the past”.

Through what methodology do we know what the past heights of mountains were?

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    $\begingroup$ This is a loose, even negligent, statement, as "they were in the past" is undefined. A certain nr. of millions of years ago, the Indian subcontinent had not generated the Himalayan-Karakorum mountainous range. $\endgroup$
    – DanielC
    Jul 17, 2021 at 22:57
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    $\begingroup$ @DanielC it might not be as bad as that; certainly Feynman was talking about an ensemble average like an RMS roughness for the planet, not a specific tallest mountain. It certainly might be wrong (and Feynman was no saint when it comes to other things); but "negligent" doesn't generally apply to things that Feynman wrote. Then again, The Feynman Lectures on Physics were actually written by coauthors are Feynman, Robert B. Leighton, and Matthew Sands so we can't be sure these exact words were spoken verbatim during a lecture. $\endgroup$
    – uhoh
    Jul 18, 2021 at 3:23
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    $\begingroup$ I think it could just be a phrasing for uniformitarianism: en.wikipedia.org/wiki/Uniformitarianism $\endgroup$ Dec 26, 2022 at 9:08
  • $\begingroup$ On second thoughts, if you are looking for methods to determine the past height of mountains, there is a whole discipline about it called "paleoaltimetry". There is a whole book about it: doi.org/10.1515/9781501508608 The main method is based on stable isotopes. $\endgroup$ May 25, 2023 at 13:13


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