I’m never sure whether to trust arXiv papers outside my field, so I checked and found that the paper was published in the International Journal of Astrobiology,

I’m never sure whether to trust arXiv papers outside my field, so I checked and found that the paper was published in the International Journal of Astrobiology, and the PDF is open access: https://www.cambridge.org/core/journals/international-journal-of-astrobiology/article/silurian-hypothesis-would-it-be-possible-to-detect-an-industrial-civilization-in-the-geological-record/77818514AA6907750B8F4339F7C70EC6 https://www.cambridge.org/core/journals/international-journa...