We know that the current SETI efforts have not found evidence for the existence of intelligent exo-civilizations (XCIV). There also has not been any evidence found of ancient non-human civilizations in the fossil record. One possibility, among many, is that XCIVs only exist for a geologically short amount of time before collapsing/extinction. Then, it could be possible that, even though none exist now, one or more XCIV could have existed in the past, and it was capable of transmitting electromagnetic (EM) radiation signals.
So, consider the following hypothesis:
- In the last 100 million years, at least one XCIV capable of emitting directed EM radiation existed within 100 light-years of our solar system.
- The CIV sent directed EM beams towards all the planets in the star systems surrounding it.
- Based on what it could detect about each planet's composition, it designed the beams (frequency, signaling pattern, modulation, etc...) such that they would leave as large of a mark on the targeted planet's geologic record as possible (the mark).
Question: Is there any form of patterned, extra-solar EM radiation that could theoretically leave a mark in the geologic record that could be recognizable to us as such up to 100 million years later? And could a human-level civilization be capable of projecting such beams?