Advanced civilizations should leave a mark after their disappearance. But are we able to detect it after millions of years?
Could we tell if an advanced civilization lived on Earth millions of years ago - short science news

Let us imagine the following scenario: millions of years ago Earth was dominated by an advanced civilization that survived for thousands of years until they mysteriously vanished. If this was true, could we find traces and clues for their existence? This is exactly what scientist tried to understand in a recently published study. They show that the chances of finding direct evidence (artifacts, fossils) for civilizations older than 4 million years are extremely small. However, clues could be provided by geological records (due to the industrial impact on the planet), stable isotopes anomalies, non-natural elements and etc. The paper makes for a very interesting reading and it shows us what to look for in the search for previous civilizations on Earth, or on other planets.

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Scientific publication: International Journal of Astrobiology