According to Frank and Schmidt, since fossilization is relatively rare and little of Earth’s exposed surface is from before the quaternary time period, the chances of finding direct evidence of such a civilization, such as technological artifacts, is small. After a great time span, the researchers concluded, we would be more likely to find indirect evidence such as anomalies in the chemical composition or isotope ratios of sediments.[3] Objects that could indicate possible evidence of past civilizations inc
Source: Silurian hypothesis – Wikipedia
Tim B.
https://www.theatlantic.com/science/archive/2018/04/are-we-earths-only-civilization/557180/
“It’s not often that you write a paper proposing a hypothesis that you don’t support. Gavin and I don’t believe the Earth once hosted a 50-million-year-old Paleocene civilization. But by asking if we could “see” truly ancient industrial civilizations, we were forced to ask about the generic kinds of impacts any civilization might have on a planet. That’s exactly what the astrobiological perspective on climate change is all about. Civilization building means harvesting energy from the planet to do work (i.e., the work of civilization building). Once the civilization reaches truly planetary scales, there has to be some feedback on the coupled planetary systems that gave it life (air, water, rock). This will be particularly true for young civilizations like ours still climbing up the ladder of technological capacity. There is, in other words, no free lunch. While some energy sources will have lower impact—say solar versus fossil fuels—you can’t power a global civilization without some degree of impact on the planet.”