The Silurian hypothesis

How many hightech civilizations might have risen & fallen on a world that is about 4.5 billion years old? Well, the Silurian_hypothesis provides a fascinating thought experiment.

https://en.wikipedia.org/wiki/Silurian_hypothesis#In_popular_culture

https://www.discovery.com/exploration/Advanced-Civilization-Silurian-Hypothesis

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

Just over the past billion years, a lot of unknown civilizations could have started up.

https://www.theatlantic.com/science/archive/2018/04/are-we-earths-only-civilization/557180/