Humans have occupied the Earth for less than 0.1% of its total existence. Given the vastness of time and the incompleteness of the geologic record, is it possible that the Earth had independently produced another intelligent species in the remote past? By extension, given the lack of fullness of knowledge regarding the deep history of our solar system, could other worlds have been host to such intelligences? And if it is possible, is it a worthy endeavor to pursue answers to these questions? This is the situation presented to us by astronomer Jason Wright in his paper regarding the possibility of what he calls prior indigeneous intelligent species, that is, intelligences which arose organically (i.e., not from other star systems) within our own solar system.
For many modern astrobiologists, there is hope that extant or extinct life will be discovered on perhaps Mars or the moons of the gas giants, but Wright is distinct in his pursuit of the possibility of the development of a more complex lifeform in the solar system. He considers a variety of plausible lines of evidence we could follow to establish whether or not the Earth or any other body of the solar system could have harbored an intelligence in the distant past. In the case of the Earth, it is difficult to conceptualize a way for artifacts or other signatures could be preserved on lengths of time comparable to the age of the Earth, but one strong marker would be unnatural isotope ratios discovered in sedimentary layers indicative of nuclear activity. Since some radioactive atoms have half-lives of billions of years, their signal should still be active even given the eons. For other bodies, those with geologic activity and atmospheres tend to continually renew their surfaces wherease those without are at the very least impacted frequently by micrometeorites and infrequently by asteroids. This reduces the probability that any actual physical relicts would ever be detected. Also, relics in orbit would tend to decay or scatter or collide with other objects, and hence are unlikely to survive the temporal expanse.
Even with the apparent implausibility of any success, I would agree with the author and argue that there is a small place for this area of inquiry so long as it does not detract from the pursuit of more secure science. If indigenous species’ artifact searches can be performed in the background using data that is already acquired, then I feel that there is no harm in at least exhausting the possibilities.