What if we’re looking for alien life in all the wrong places? In response to the current search for alien life in sources beyond Earth, Penn State astronomer Jason Wright has published a paper titled "Prior Indigenous Technological Species", putting forth the idea that there’s the possibility that we mightn’t have to look too far afield to find traces of technologically-advanced alien civilizations, as there may very well have been some that evolved right here on our own planet, in Earth’s distant past.
When we think of the possible ancient civilizations that may had existed on Earth, we tend to only think of tens of thousands of years into the past, like in the case of Atlantis, or hundreds of thousands of years, as would be the case presented by authors such as Erich von Däniken or Zecharia Sitchin. But life itself, in one form or another, has been present on Earth for one-third of the existence of the entire known universe — plenty of time for any number of technologically-developed species, and their resulting civilizations, to wax and wane. Considering the haphazard nature of unveiling the fossil record, and that over seventy percent of Earth’s potential paleontological record is hidden underwater, multiple ancient civilizations from deep in Earth’s past could easily have come and gone without our knowing.
Wright proposes the possible existence of what he calls an "indigenous technological species" — indigenous, because it would have evolved in this solar system, as opposed to having originated from another star. Regardless of the true nature of the stories, the Anunnaki from Sumerian myths would count as an example of this, reputedly having come from a planet from within our own solar system. Wright posits that if the technologies of such a civilization were made of materials that were designed to withstand the rigors of time, artifacts constructed from these materials — technosignatures, as Wright calls them — could still be present somewhere on Venus or Mars, or perhaps even in a still-undiscovered location on Earth.
And Wright suggests that Earth is probably the best place to look for such a lost civilization. We know virtually nothing about the potential biospheres that may have existed on Venus or Mars; however, Earth’s Cambrian period was a sudden explosion of diversity in the number of different lifeforms that occurred half a billion years ago. Considering how many extinction-level events have happened since the beginning of that period (specifically, five really big ones), that means that that biological reset button had ample opportunity to put an end to the advancement of any technological cultures that may have been caught up in those events.
There is also the question regarding whether or not we’d even be able to recognize such technosignatures if we were to stumble across them: the nature of such devices, even if the concept involved is remarkably simple, might be so alien to our culture as to be beyond our recognition.