Astrobiologist, physicist, and cosmologist Paul Davies has cooperated with SETI for thirty years, but believes scientists might have better luck finding evidence of extraterrestrial life here on Earth. According to Astrobiology Magazine, “Davies wants scientists to broaden theirthinking about how aliens could have left behind their mark.” He suggests that scientists should search our own planet for possible “footprints” left behind by ancient extraterrestrial visitors, “or even analyze the DNA of terrestrial organisms for signs of intelligent messages or tinkering.” He explains that it is possible that intelligent extraterrestrials visited Earth long ago, and therefore there could be evidence of their visit, but “probability and the length of the universe’s age suggest that any such alien visit would have taken place before humans ever emerged on Earth.”
The evidence could be on our very own planet. We just have to find it. That is, if any traces of extraterrestrial visitation have survived for “hundreds of millions or billions of years for humans to still find them today.”
Davies feels that the search for evidence of extraterrestrial life here on Earth would complement SETI’s skyward efforts, even though he acknowledges that using radio telescopes to listen for alien signals is like searching for a needle in a haystack.