Intelligence before humans??

Wright (2017) explains that that searches for ETI should include searches within the solar system. He argues that it is a good place to look (either for extant or extinct life), because it is near the only place we for sure know harbours life, Earth. He argues that life could have arisen on other bodies in the solar system (namely Venus, Mars, maybe the moon, the icy moons, and possibly asteroids or KBOs), and mentions that it is even possible that a prior species on Earth arose before humans that was intelligent.

I agree with many points in this paper. I believe that SETI should include solar system searches, especially because of the data we already have for many of the bodies. This links back to the argument by Davies and Wagner (2013) that SETI should be done not based on the possibility of discovery, but based on the time and effort the search would take. Solar system searches take remarkably less time since the objects are closer to us.

Wright points out that Venus could have been a good host of life before it lost all of its water and went runaway greenhouse. Unfortunately, Venus has such a young surface from its volcanic flows that any evidence older than a couple hundred million years would be completely erased, and any evidence prior would likely be erased too. Mars is a decent target since it was probably wet once and capable of hosting life before it lost almost all of its atmosphere, but weathering on its surface is decent and any artifacts would probably be covered by now. Other objects in the solar system and their associated datasets should be searched for technosignatures though.

That being said, there is a point in Wright’s paper that I very much disagree with, and that is the possibility of an intelligent species before humans. While I will grant that the fossil record is horrifically incomplete, one flaw I find in this suggestion is the need for oxygen. Our planet was very anoxic before about 500 million years ago, and the rise of life is highly correlated with rising oxygen levels. While any life could have been anoxic, most astrobiologists search for life that requires oxygen since it is the only life we know. Wright is calling for an analysis of ancient facies in search for technosignatures; I think this exceeds the “low cost” criteria, especially given that a successful search requires the assumption that any life inferred did not require oxygen. On top of that, although the fossil record is lacking, there is no indication of any line of evolution that was anoxic, nor evidence of a rise in intelligence that went extinct (unless we include intelligent dinosaurs?). This suggestion just seems fanciful to me; although it would be kind of neat, we have absolutely no reason at all to believe that such a species arose, no evidence of anything that could destroy such a species (except maybe KT?), and any intelligent life would need to be anoxic and would defy our current understanding of life.